Ignition (key on) fuse?

[eaks]

Hello,

I've been working on my 04 viper for the past few days. I installed a wideband sensor (exhaust was removed, then I welded the **** and reinstalled in car).. When installing the gauge for testing I was going to just run it off the unit for power.. I have an aftermarket hesd unit so figured it wouldn't be bad to hack up the harness on the hesd unit side incase I mess anything up..

I wired it up and turned the car on and I get nothing (wideband gauge doesn't turn on and neither does the head unit). I used a jumper on the harness to jumper the constant 12v to the red wire (key on). When I did this the head unit worked and my wideband gauge turned on as well..

I checked all the fuses under the hood and they were all good.. I can't seem to find a wire schematic that shows the key on to the stereo and where this power comes from and where a possible fuse could be. The head unit worked fine a week ago when I last drove the car.

I did a bunch of work under the car (removed skip shift and removed the reverse lockout solenoid).. Then pulled the exhaust and installed my wideband.. Today was the first time I tried to turn the ignition on since starting any of the work.

I was able to start the car and everything seemed perfect when it was running (but no wideband or head unit).. I originally tried to turn the ignition on with the Hvac and start button unplugged then when I didn't get power i thought maybe I needed these modules plugged in.. Plugged them all in and same outcome (no key on power to hesd unit).

Anyone have any ideas or the wire schematic for the head unit on these cars?

 

[Old School]

Schematic around radio.

 

[Steve M]

I can't directly answer your question, but will at least offer this - when I installed a wideband on my car, I installed an add-a-fuse in the 15-amp gauges fuse slot in the engine bay.

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Ran the wire from there through the firewall next to the brake booster (towards the outside of the car) and into the cabin. I ran the wire to a small fuse block that sits on a sort of shelf on top of the transmission tunnel pretty much under where the radio sits...it powers multiple things including my shift light and wideband controller.

I'm guessing that circuit is the same on both the Gen 3 & 4, but don't know for sure.

If so, that's an option, although it doesn't really help your current situation.

 

[eaks]

Schematic around radio.

Do you know where the relay is that feeds the acc power to radio? I'm wondering if I knocked a relay loose while running my wiring around the dash.. I'll go out and have anothrr look and hopefully get it sorted.

And steve: yes that was my plan to run a hot wire into the cabin but I wanted to make sure everything else was working before I seal up the grommet in the firewall..

 

[eaks]

Well just an update.. I wired the gauge to the gauges fuse under the hood as shown above by Steve. I wired the hesd unit to this as well as the hesd unit wasn't working.. I also back fed the acc wiring from the deck and with this connected both the afr gauge and the deck turned on with the key but wouldn't ever turn off.. I then just removed the acc wire and just tied the gauge tapped power to the afr gauge and the headunit..everything seemed to work fine and I went out for a drive.. A buddy of mine got stranded in his range rover so I drove out to give him a hand and put some miles on the viper to see how jt all works.

Only thing that was weird was that it wouldn't release the key.. I stopped a few times running to the parts store and my buddies house for random odds and ends and the key would never release.. Then when I got home the key released fine.. Really not sure if that has anything to do with what's going on with no acc power to the head unit or not.. Real head scratcher

 

[eaks]

Through the car up on the lift today as I wanted to return my reverse lockout solenoid. I found with my ipsc short shifter going to 5th I had to focus to not go over much and hit reverse.. Never got it in reverse but did go over and hear some grinding from the synchros so I decided it's best to leave it it. Additionally my 6th gear issue wasn't solved by the reverse lockout (it was wishful thinking).. I need to either double clutch to get into 6th or give it 2-3 seconds out pressure off and on the shifter until the trans wants to accept 6th gear)..

Good news is the key release worked the 3 or 4 times I started the car this morning moving around and test driving.. I may pop the dash off again and take measurements and see if the acc power is now actually coming from the bcm or not (if it is u will most likely wire the deck to this power and keep my seperate fused wire for my afr gauge and my **** controller when i install that