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Discussion Starter · #1 · (Edited)
*** Complete - If you have any questions about anything, please ask before proceeding. If you think I may have written something incorrectly, please let me know and I'll review ***

As most C7 owners know, there's no factory setting for the NPP exhaust that keeps the exhaust valves open ALL the time. Track mode keeps them open MOST of the time, but they still close in certain gears at speeds below 36-37mph to pass federal noise regulations. So some owners pull the NPP fuse (fuse 41 on 2014s, fuse 42 on 2015s and later), which forces the NPP valves open all the time. The downside is that there are times we might want the exhaust to be quieter*, and opening the hood and fuse box to reinsert the fuse is sort of a pain.

* I like to keep the neighbors happy by quieting things down when I fire up the car at 6:00 a.m., or even later on a weekend. I also get tired of the drone with the pipes open on a long highway trip, so being able to quiet things down then is nice, too.

This mod installs a small wireless relay board inside the C7 front fuse box that allows you to essentially “pull the fuse” remotely using a small 2 button key fob remote. When the “Off” button on the remote is pressed, the fuse is removed from the circuit, and the NPP valves will remain open all the time. When the “On” button is pressed, the fuse is inserted in the circuit, and the NPP valves operate normally. If you have the exhaust set to follow drive mode, it will still do that. If you set the exhaust to “Stealth,” it will always be quiet when the “On” button is pressed. If you have a 2LT or 3LT with Homelink buttons on the visor, you can program 2 of those buttons to emulate the On and Off buttons on the remote. This modification does not involve cutting or modifying any existing wiring, and is completely removable and reversible if you don't want the dealer to see your modifications.

Note that this will do nothing to prevent the AFM valves on an automatic C7 from closing whenever the car goes into 4 cylinder mode. See post #4 for more about the AFM valves.

NOTICE: If you decide to construct and install any hardware based on the information below, you agree to use it at your own risk. If you short out your wiring harness or otherwise damage yourself or your car, I assume no responsibility and accept no liability whatsoever. The circuit appears straightforward, has been used successfully by others and works well for me. If you decide to attempt to build and install the exhaust valve controller, read the full post a couple of times before proceeding. If in doubt about the procedure or your ability, think twice before proceeding and ask questions as there are people on this forum who know much more about the modern electronics in these cars than I do. All work done within the fuse box while the cover is removed must be done with the ignition OFF.

IF YOU FEEL THIS IS TOO COMPLICATED FOR YOU TO DO, THERE IS A COMMERICAL PRODUCT FROM Mild2Wild THAT DOES THE SAME THING (ALBEIT FOR A HIGHER PRICE, AND POSSIBLY A SOMEWHAT LESS CLEAN INSTALL.)

CAUTION: All the existing fuses in the fuse box have live metal tips flush with the top of the fuse (see below). It is critically important that no exposed metal surfaces come in contact with these contacts. Allowing any bare contacts to come in contact with one of these live fuse tips could create an unfused short to ground. That would be very bad. This is very easy to prevent, but understand there is a reason for everything in this procedure. Don’t skimp on any steps. If I’ve shrink-wrapped something, there’s a reason for it. The circuit board used has bare contacts on its bottom, that must be insulated from the fuses. NO BARE WIRE OR EXPOSED CONTACTS ARE ALLOWED IN THE FUSE BOX.


exposed fuse contacts (top).jpg

This write-up refers to replacing Fuse #42 in the front, underhood fuse box. This is correct for 2015 and 2016 C7s, and I believe 2017s. If you have a 2014 C7, the correct fuse is #41. The fuse is located in the same location on all model years, but is numbered differently.

Parts required:

(1) iMBAPrice® 12V, 15 Amps, Heavy Duty Boat and Car Universal Remote Control Kit, Amazon.com and quite a few other online resellers, $17. They come in different brand names, but they all appear to be the same. The one from iMBAPrice is the one I've used for a couple of different projects. Comes with two remotes.
remote relay pic.jpg

(1) Lumision ADD-A-CIRCUIT ATR MICRO2 FUSE-TAP Add ON DUAL CIRCUIT ADAPTER AUTO CAR TERMINAL + 5 AMP Fuse, available from Amazon.com, and possibly your local auto parts store. About $8. Make sure you get a Micro Fuse Tap, and not a Mini Fuse Tap. Ask me how I know. ;)
micro fuse tap.jpg

Note: the included 5amp fuse will be harvested later for parts.

(1) 14-16 gauge (blue) blade connector, bent as shown. Available from your local auto parts or hardware store.
Ground Lug Terminal 1.jpg

Shrink Tubing. Available from Amazon, and many other places including, maybe, your local auto parts or hardware store.

Shrink Tubing.jpg
 

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Discussion Starter · #2 · (Edited)
Steps 1-7 can be done away from the car. Actual installation of hardware into the car starts with step #8.

Connecting the Power Leads

Step 1: Remove the screws and pry plastic case lid off of remote control black box to reveal circuit board. Remove small Philips-head screw from circuit board and remove board from case bottom. Reserve the case and screws, as we’ll be reusing them later.

Step 2: Shorten red wire coming from circuit board to about 1 1/2 inch total length. (You might want to leave it long for the initial install, and then go back and redo it later. It’s easy to loop the excess wire inside the fuse box, but a lot harder to stretch the wire if you cut it too short.) Strip 3/8" off of free end of red wire.

Step 3: Attach the wire from the Fuse Tap to the red wire from the circuit board. You have several options here. The easiest way is to simply use the crimp connector that’s already attached to the fuse tap. Alternately, you could cut off the crimp connector and solder and shrink wrap it. If you choose this option, you’ll need to leave the red wire coming from the circuit board longer.

Red Wire Connection to Fuse Tap.jpg

Step 4: The Fuse-Tap Add-A-circuit comes with a spare fuse. Using wire cutters, or a utility knife, or a small saw blade (not scissors) cut the spare fuse in half and trim off the plastic case until you have just one of the metal legs as shown below. Save the other piece, just in case you mess up soldering the first one.

Fuse Leg.jpg

Step 5: Shorten white wire from circuit board to about 3" long. (Again, you can leave it long and just loop the extra wire inside of the fuse box.) Slide a short piece of heat shrink over the wire and strip off 5/8" of insulation off the end of the white wire. Solder the end of the white wire to the skinny half of the fuse leg you harvested from the spare fuse in step 3. Slide the heat shrink up to cover joint and heat the shrink tubing as shown below.

Fuse Leg soldered to white wire.jpg

Step 6: Attach the lug you soldered to the white wire to the fuse tap, as shown above in Step 3. It’s kind of hard to see in that photo, but it goes in the slot indicated by the arrow, below.

Fuse Tap connections_.jpg

Connecting the Ground Wires

The two black wires from the circuit board are ground wires. These need to be attached to the bent spade lug. First, though, an explanation.On my first version of this, I routed the ground wires outside the fuse box to a ground stud located under the hood. This potentially affects the seal of the gasket around the fuse box lid. I never had any issues, but over many years could be a potential problem. Since then, I found an article elsewhere on the internet that identified a ground location inside the fuse box, and a method for tapping into that ground. This makes for a much cleaner install, with no wires exiting the fuse box. The steps below use this improved method.

Step 7: Attach the 2 black ground wires to the bent lug. Be sure to cover all exposed surfaces with shrink tubing, as shown. You want to be sure no exposed part of the lug can contact the relay case. Be sure to read the next post in full before cutting the ground wires.


Ground lug heatshrink.jpg
 

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Discussion Starter · #3 · (Edited)
Under the Hood

Open the hood, and pop the top off the fuse box by pulling forward on the two tabs located on the front of the fuse box. Lift up the front edge of the lid, and pull forward and up. If you’ve never had it open before, it may take a fair bit of force to pull it loose. Note there are two tabs on the rear of the lid that fit into slots at the rear of the fuse box. The lid will only fit one way when you go to put it back on.

What follows is backgound information, so you understand what we're going to do. Actual installation begins with Step 8.

The Vac Pump Relay at position 63 is a "Ground Switching" relay, so pole 87 has a continuous ground, regardless of the state of the cars electrical system. We’re going to tap into that ground. This is the location of Relay 63:

Ground Lug Relay location.jpg

In Step 9, we’re going to remove (and later reinstall) this relay, sharing the ground location. The photo below shows why we need to bend the lug and remove part (or all) of the blue plastic.

Ground Lug Terminal 2.jpg

We’re going to connect the black ground wires from the relay to the lug terminal, and route them as shown below, then reinstall the relay and lug simultaneously.

Ground Lug installation location.jpg

The photo below shows the wires, lug and relay after installation.

ground lug closeup.jpg

Important: All wiring in the fuse box must be done with the ignition turned OFF.

Step 8: You can, at this point, proceed to installing your prewired relay assembly in the fuse box. But remember the warning about the contacts on the bottom of the circuit board. You MUST insulate the board from the fuses. The first time I did this, I covered the bottom of the circuit board with a couple of layers of electrical tape, and put a piece of closed cell foam, about 3/4 inches thick, between the bottom of the circuit board and the fuse box. This insulated the contacts, and pressed the circuit board against the top of the fuse box, keeping it from moving around. Here’s a photo of that assembly. (Note that I wasn’t using the internal ground at this point, nor had I trimmed the wires to a shorter length.) If you want to do this, perhaps to test before going further, proceed to step 8.

small - relay board in place - original.jpg

8a: Make sure the ignition is OFF. Pull fuse 42 (41 for a 2014), and insert it in the top slot on the fuse tap, as shown in step 3. Push the fuse tap in where the fuse came out. Be sure to orient the fuse tap as shown above, with the red wire pointing towards the front of the car. Make sure you don’t loosen the white wire that’s inserted into the fuse tap.

8b: Pull out relay 63 by pulling straight up. You can wiggle it a little bit, but you don’t want to bend any contacts. (It’s not hard to do, just exercise reasonable care.) Insert the ground wire lug as shown above, and reinsert the relay.

8c: Test. (Don’t forget to have some kind of insulation between the bottom of the circuit board and the fuses.) Put the car into Service Only Mode by pressing the start button, without pressing the clutch pedal, and holding it for 8 seconds. The dash should light up as if you were starting the car. Now, standing by the fuse box, press the On button on a remote. You should be able to hear the relay on the circuit board click. Press the Off button. It should click again. If you don’t hear any clicks, shut off the ignition and make sure all your connections are good: crimp or soldered connections are tight; the fuse and the white wire are inserted firmly into the fuse tap, and the fuse tap inserted firmly into the fuse box; and the ground lug and relay firmly seated. ALWAYS shut the ignition off before connecting or disconnecting anything in the fuse box.

Assuming you hear the clicks, shut off the ignition. Then start the car. Put the exhaust in Tour or Stealth Mode. Click the On button. The exhaust should get quieter. Click the off button. It should get louder. If you’re happy with leaving the circuit board exposed, you can stop here, put the cover back on the fuse box, and you’re golden. Skip to step 11. But if you want a cleaner, more professional looking install, keep reading.

Note: Full credit to member “Ratz” on another Corvette Forum, who devised the technique of grounding the circuit through the relay and making the plastic box fit, and whose photos of the relay setup and box shortening technique (below) I shamelessly borrowed.

Step 9: Ideally, we’d want to leave the circuit board inside the plastic box it came in, but the box is too big to fit inside the fuse box. So let’s make the box smaller! We need to cut 1/2 inch in length out of the box. You can assemble the box and cut 1/2 inch out of the middle. Ratz cut each piece individually, to offset the cuts. I think this makes the final assembly a little bit stronger. See photos (Thanks Ratz!) below:

Box with cuts marked.jpg
Box with cuts made.jpg
Circuit board inside cut box.jpg
Cut box assembled.jpg

Now you can install the mounted circuit board in the same location I showed in Step 8, with no concerns about any exposed contacts. I would still suggest putting a layer of foam under the fuse box to ensure it can’t move around or rattle.

Important: All wiring in the fuse box must be done with the ignition turned OFF.

9a: Pull fuse 42 (41 for a 2014), and insert it in the top slot on the fuse tap, as shown in step 3. Push the fuse tap in where the fuse came out. Be sure to orient the fuse tap as shown below, with the red wire pointing towards the front of the car. Make sure you don’t loosen the white wire that’s inserted into the fuse tap.

9b: Pull out relay 63 by pulling straight up. You can wiggle it a little bit, but you don’t want to bend any contacts. (It’s not hard to do, just exercise reasonable care.) Insert the ground wire lug as shown above, and reinsert the relay.

9c: Test. Put the car into Service Only Mode by pressing the start button, without pressing the clutch pedal, and holding it for 8 seconds. The dash should light up as if you were starting the car. Now, standing by the fuse box, press the On button on a remote. You should be able to hear the relay on the circuit board click. Press the Off button. It should click again. If you don’t hear any clicks, shut off the ignition and make sure all your connections are good: crimp or soldered connections are tight; the fuse and the white wire are inserted firmly into the fuse tap, and the fuse tap inserted firmly into the fuse box; and the ground lug and relay firmly seated. ALWAYS shut the ignition off before connecting or disconnecting anything in the fuse box.

Assuming you hear the clicks, shut off the ignition. Then start the car. Put the exhaust in Tour or Stealth Mode. Click the On button. The exhaust should get quieter. Click the off button. It should get louder.

Completed installation: The blue wire is the antenna.

Installed assembly.jpg

Step 10: Reinstall the fuse box cover by inserting the tabs on the rear of the cover into the corresponding slots, and press the front of the lid down until both latches click shut.
 

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Discussion Starter · #4 · (Edited)
Operation of the remote, and Homelink programming

Step 11: Operation is pretty straightforward. Pushing the Off button on the remote removes the fuse from the circuit, and the NPP valves are open. Push the On button, and the fuse is reinserted into the circuit, so the system operates normally. A couple of things to keep in mind, though:

11a. The default position for the relay is always “Off.” That means the car always starts in loud mode, with the NPP valves open. You can get around this by holding the On button while starting the car. The relay will turn on and quiet the exhaust within a split second.

11b. Pressing the On button doesn’t mean the exhaust is quiet. It means the NPP valves are controlled by the car, as usual. So if you have the exhaust mapped to driving mode, and the mode dial in Track, the exhaust is still going to be loud. If you want the remote to truly switch between loud and quiet, go into the Infotainment screen and set exhaust mode to Stealth or Tour. 2014 owners, I'm sorry, but you don't have this option.

11c. If you have an automatic, note that this mod does nothing about the AFM valves located ahead of the mufflers. Anytime the computer puts the engine into 4 cylinder mode, the AFM valves will close partially, quieting the exhaust. You cannot use this mod to "pull" the AFM fuse. Pulling that fuse will generate a Check Engine Light. The only ways to prevent the AFM valves from closing on an automatic equipped C7 are to put the shifter into manual mode, to use a Range Disabler (search the forum for more info), or get an ECU tune (which can impact your warranty).

Programing the Homelink buttons

If you have a 2LT / LZ or 3LT / LZ, you have three Homelink buttons on the driver’s sun visor. You probably have one programmed to operate your garage door. If two of the buttons are not in use, you can program one to turn the relay On (quiet) and the other to turn the relay Off (loud). Instructions for programming these are in your owners manual, an also below:

Homelink programming 1.jpg

These buttons will then work exactly as do the buttons on the remote. Hold the button you programmed as “On” while starting the car to have it start in quiet mode.

If you have a 1LT without Homelink, you’ll probably want to mount one of the remotes in a convenient location. I put a piece of Velcro on the back of mine, and stuck it to the carpet on the side of the console, where I could reach it easily.
 
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I had the Mild2Wild setup on my 2013 Camaro SS and really liked the ability to control the exhaust valves with a simple press of a home link button. Subscribed!
 

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Wow that is an excellent idea...I might be willing to try this mod after your writeup.
 

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Many thanks in advance :victorious:
 

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Discussion Starter · #10 ·
OK, it's ready to go. Please read all of the first three posts before beginning your install. If anything doesn't make sense, or you're not sure you follow anything, or you think I wrote something incorrect, please ask before proceeding.

NOTICE: If you decide to construct and install any hardware based on the information above, you agree to use it at your own risk. If you short out your wiring harness or otherwise damage yourself or your car, I assume no responsibility and accept no liability whatsoever. The circuit appears straightforward, has been used successfully by others and works well for me. If you decide to attempt to build and install the exhaust valve controller, read the full post a couple of times before proceeding. If in doubt about the procedure or your ability, think twice before proceeding and ask questions as there are people on this forum who know much more about the modern electronics in these cars than I do. All work done within the fuse box while the cover is removed must be done with the ignition OFF.
 

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Nice work and Great instructions! We did ours last year on the Z06 and IMG_0494.JPG two years ago on the Z51 almost identical other than the one outside the fuse box for the ground. IMG_0493.JPG
 

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Just finished build and install on my 2014 3LT and I must say your directions are awesome!!!
I might add that I wanted ON to open (loud)exhaust and OFF to close (quiet)all you need to do is open remote and turn to ON OFF pad round.
Love the DIY mod many thanks for posting
 

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Discussion Starter · #13 ·
Cool! Never thought of that idea. But since I've programmed my Homelink buttons, I don't use the remote any more anyway.

Glad you like it. Anyone else going to try?
 

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Anyone else going to try?
There will certainly be dozens, possibly hundreds, of do it yourself C7 owners who use this guide over the coming decade.

Honestly, I can't recall seeing another "how to" thread organized and documented this nicely.

Well done.
 
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Discussion Starter · #15 ·
Honestly, I can't recall seeing another "how to" thread organized and documented this nicely.

Well done.
Thank you! But did you see my wireless parking camera thread, or my SmartTop install thread? All my how-to's are this anal. :D That's what decades of coding, testing, writing specs, and managing software projects does to you.
 
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Ok, am I missing something? I just bought a 2016 Z51 and it gives me the option to select the exhaust setting through the infotainment screen and decouple it from the drive mode that I'm in. What would be the advantage of doing this? And as others have said, excellent write up!
 

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I had the mild-to-wild on my 2012 that I can't use on my 2016. If interested PM me and I'll sell it to you for a reduced price. ?
 

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Discussion Starter · #18 ·
Ok, am I missing something? I just bought a 2016 Z51 and it gives me the option to select the exhaust setting through the infotainment screen and decouple it from the drive mode that I'm in. What would be the advantage of doing this? And as others have said, excellent write up!
Even if you set the exhaust to "Track" mode in the infotainment screen, the valves don't actually stay open all the time. In order to pass federal and state sound level standards and tests, the NPP valves will close in certain gears at speeds below about 36 - 37 mph. Some people don't care, but some people don't like the car quieting down when you slow down.

By pulling the fuse, either physically or via a mod like this, you force the valves to remain open ALL the time. This mod lets you "pull the fuse" when you want, but still quiet the car down when you need to.
 

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Even if you set the exhaust to "Track" mode in the infotainment screen, the valves don't actually stay open all the time. In order to pass federal and state sound level standards and tests, the NPP valves will close in certain gears at speeds below about 36 - 37 mph. Some people don't care, but some people don't like the car quieting down when you slow down.

By pulling the fuse, either physically or via a mod like this, you force the valves to remain open ALL the time. This mod lets you "pull the fuse" when you want, but still quiet the car down when you need to.
I see. Thank you for clarifying.
 

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Discussion Starter · #20 ·
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