I need the members help!. 2000 C5 Convertible with 126000 miles. I have no parking lights, no front turn signals but the rears flash very fast, no fog lamps, no tail lights, no dash lights but the headlights work both low and high beams. The brake and back up lights work. The hazzard flashers work on the rear only and seem normal. The car was sitting for a year with a dead battery so at first there were many DTCs but I went in and reset them and now I have no DTC codes in any of the modules and no blown fuses. The previous owner had installed a toggle switch that put a ground on the A5 circuit (parking lights) by cutting the yel/bl wire that goes into A5 on the C3 connector of the BCM. I removed that switch and spliced the wire back together. It also has a solid state relay installed by the BCM for the column lock. It's as if everything from the firewall forward is defective. I have disassembled and cleaned the grounds by the headlights with no change. Do I have an issue with the BCM or the headlight switch or is there something else I am overlooking? I've read the postings and those two seem to be the issues but the lack of DTC's has me puzzled.

Any guidance would be appreciated

 

So, in your opinion, the BCM is not the issue?

Thanks for taking the time to respond.

 

The only odd one not related to the MFS is the hazards. The hazard switch bypasses the MFS and should make the front lights flash even if the MFS was disconnected. Everything else could be explained by a badly messed-up MFS.

By the things not working, I would still almost suspect more than one failure point. A bunch of specific contacts in the MFS would have to fail exactly right to make the failures you have occur.

Do the front signal/running lights aka the daytime running lights or DRL come on with the car running and no lights on? If they don't, then I would suspect the front signal issues are caused by someone messing with the relays for the front signal lights to eliminate the DRL function.

 

I have no DRL lights. Your comment is sort of what I was thinking. That's a lot of stuff for one switch to affect. Given the toggle switch that was in there, I tend to agree with you that perhaps something else is not kosher. I will either repair or replace the switch and I have already ordered a new hazzard switch. That should at the very least, narrow down my search field.

Thank you very much for your help.

 

I've replaced the multifunction switch and the hazard switch. I now have everything from the firewall back. I have front marker lights but no DRL, Turn Signal, Fog or flashers. I have headlights both low and high beam.
In reading thru the AllData files, they talk about the Ambient Light Sensor. I looked at the dash grill and this car does not have one. I had the dash pad off and there is no loose harness under there that would connect to the sensor. First, does this car have to have one and second, could this be why my DRL lights don't work?


Thanks

 

I had the dash pad off so it required taking the grill out of the front of the pad. There is a large hole on the drivers side where the sensor should be and no wires dangling or tied off in the dash area. I'll look for the relays next and then check the BCM plug for the correct wire.
As I read the owners manual, the sensor in question is used for Twilight Sentinel/Automatic Headlights and since I don't believe this car has either option, maybe it wasn't supposed to be there. Maybe?

 

I'm good with the diagrams. That electrical engineering degree comes in handy sometimes. Its just very difficult to sort out the options and what someone else may have done to the wiring. I checked all 13 ground points and associated splice packs and they are all cleaned and reassembled. I put 12v AFTER the relay that controls the fog lights, taking the BCM out of the picture and they still don't come on.
If it ever stops raining here I'll pull the panels off and check for the relays you noted and then double check that the bulbs are good.