m3to335

I don't know how long this has been going on since I rarely walk around the back of my car to see if the running lights are on. Saturday I left early in the morning and noticed the tail lights weren't lit. Here's what works and what doesn't.

What works;
* Brake lights when depressing the brake
* Brake lights when hitting the alarm
* Headlights
* Turn signals (front and rear)
* Backup Lights


What doesn't work;
* Side marker lights
* Brake lights when just acting as running lights at night

Coincidence or not?
A long time ago some of my interior lights stopped working as well. I feel like this is all related. http://forums.corvetteforum.com/c6-c...t-working.html
What doesn't light up inside;
*Buttons surrounding the steering wheel (on the left and right of the gauge area).
*Buttons under the A/C controls
*Buttons surrounding the NAVI

I looked over the fuses and didn't see anything out of the ordinary. Where do I start looking to track down what's going on?

CGZO6

Probably not much help, but the fuse for the running lights is a red 10 amp in the underhood fuse panel.

Sounds like a short or a BCM going bad.

torquetube

As has been suggested, verify that fuse #8 is good. If it is, swap the parking lamp relay (#37) and the A/C compressor relay (#35). If the parking lamps work again and the A/C doesn't, you've got a bad relay. Otherwise, verify that the relay coil is being pulled to ground when you turn the light switch by testing the resistance between a good ground and the socket for pin 86 of the parking lamp relay. If it is, your problem is within or downstream of the fusebox. If it isn't, check the harness wiring by performing the same test at the BCM end. That should be enough to get started.

m3to335

Good information, I will do that tonight.
I didn't even know what a BCM was before all this.

1) How do I know where to check the resistance at the BCM end? Perhaps it will be more clear when I actually look at it tonight.

2) If it comes down to it, can this help me at all...
"Check the codes on the car using the DIC. That will give you a lot of information and someplace to start from. Turn the ingition to on and then push and hold the options button followed by pushing the fuel button 4 times. The car will then enter diagnostic mode and you can let loose of the options button. The diagnostics will cycle through each subsystem on the car (including the BCM) and show all codes present in each subsystem. A code is an Alhpa character followed by four numerals and possibly followed by an H or C or both the H and C. Report them back here and somebody can help you then.

Bill "

CGZO6

Sad to say, that procedure is for a C5. You need a code reader for the C6. I don't think there are any codes that will help diagnose your issue anyway.

You really need the service manuals with the wiring schematics so you can track down the issue.

torquetube

On the top of the BCM is a connector with a blue cover (visible even without pulling back the carpet). If you unlatch the connector and remove the cover, you can get at the wires. The park brake relay circuit (#1080) is the white wire at pin position #65. This should be on the bottom row toward the left. You'll need to back-pin or use an insulation-piercing probe to test the circuit with the plug connected.

A service manual set would be a good thing to have. Also, a decent (Fluke) DMM, if you don't already have one. Good luck.

m3to335

TorqueTube, thanks for the help thus far!

Here's the latest results. Everything was done with the car off and key in on position (fob, whatever you call it).

1) Swapped relays. The swap resulted in the A/C still working. Result - Relays OK.

2) Hooked a multi-meter up to pin 86 on the fuse board.
0 head lights off --> 13.5mΩ, head lights on.

3) Hooked a multi-meter up to the white wire near the BCM.
81Ω head lights off --> 116Ω head lights on

4) Disconnected my trailer light harness to take it out of the equation. No change resulted.

Honestly, I'm a bit more confused then when I started.

SSWEET

Back in my C5 days I had a very similar problem....it was the multifunction switch on the steering column......

torquetube

I'm guessing that in test #2, "0" really means infinity, and the weirdness in test #3 is because you left the relay plugged in. Is that right?

m3to335

Hmm, it's possible I left the relay plugged in for test 3. I honestly cant remember. I can do it again tonight.

I'm not quite sure what value I'm looking for though.

I always thought relays were nothing more than electric switches allowing some signal to pass by. Shouldn't one of the sockets be a hot lead that continues on it's journey to fire up the running lights? I would have thought poking my multimeter into the relay socket would have yeilded 12V somewhere.

torquetube

Yes. Fuse #8 supplies 12V to two of the relay pins at all times, car on or car off.

The contacts in the fusebox are arranged in a grid that's numbered from front to back and lettered from right to left. If you remove the relay, contact A8 and A9 should read ~12V. If not, you've almost certainly got a blown fuse.

BEZ06

YOU BLEW A FUSE!!!!!

I pull a trailer to the track as well. I've had that exact same problem twice.

The wiring from my trailer bangs around against the safety chains and has gotten chaffed enough so that bare wires shorted out.

Here's the fuse that blows:




It's the red 10 amp at the bottom right of the picture - right along the right side of the fuse box.

Bob

CGZO6

I've had the exact same issue twice. Once because I mistakenly replaced fuse 8 with a blown smartfuse (meant to put it in the skip shift slot to disable the skip shift). The second time was right after I got a new motor installed at the dealer, the tech put the smartfuse in the 8 location (didn't know until a motorcycle rider told me at 330am that my running lights were not working). Knew exactly where to look due to occurence number 1.

Bill Dearborn

If you have plus 12V at A8 and A9 then you can take a wire and apply a ground to the ground feed coming from the multifunction switch to the BCM at connector X2 pin 5 or at connector X231 pin C3. If you get no reaction doing that then apply a ground at X3 pin 8 on the underhood electrical center. If that doesn't work you will need to figure out how to apply a shorting wire between the light relay contacts A8 and C9. I would do this by using two pieces of wire with a toggle switch between them. Make sure the switch is open and plug one wire into each of the receptacles and then close the switch. Here is the Schematic. Will take a little more work to get diagrams and wiring info for connectors.



Bill

m3to335

I'm embarrassed to admit, that was the problem. I originally checked that after I hooked up the trailer. It was 5am and pitch black. It "looked" ok at the time. I was obviously mistaken and jumped to step 10 before reconfirming step one. Thanks all!


...stupid trailer!

Vacation

This is happening on my 1993 corvette LT1. The side markers and tail lights at night time would not work when turning the headlight switch on. It was at first working intermediately and then I noticed the dimmer lever on the switch was frozen so I replaced the headlight switch and it worked intermediately again for few times turning the car on and off then the dimmer switch froze again on the headlight switch. Does anyone have a wiring diagram for this car or experienced a similar situation. Where is the relay located? Thanks!

Vacation

I was able to fix the tail lights from disassembling and reassembling the switch for the headlights. Unfortunately I'm getting no lights on the dash when I turn the switch to spark the headlights and running lights. Any help appreciated going to try to tangle this tomorrow! Thanks for the time.

HoustonGrandSport

Having this same issue now. Everything OP described is happening to my car now. Going to see if the simple fuse fixes it.

HoustonGrandSport

Thank GOD it worked. Fuse #8, 10A. Tails, side markers and interior dash lights back to normal.

Dano523

Pull the rear tail light on the right hand side, and reach in to find the tail light connector for the entire back of the car lighting.
Disconnect it, clean both sides with spray electrical cleaner, add some Dielectric grease to the pins, and see if solves the problem.
If not, then double check the ground wire connection points on the rear harness next, after making sure that the bulbs and bulb sockets are still good.