I did a search but to no avail. Here is the puzzle:

Taillights not working but brake lights and turn signals do. Headlights work fine. Now this is kinda weird, that is that when I clutch the radio pauses and the heater blower does too. Same with braking. Fuses are all ok.......I haven't checked all the grounds because I am disabled and that is a chore for me. I can do it but it would help if I knew which one to check first. What say you all .....

 

OK, I'll work with you on this. I would like to know if the side lights work in the rear. Also I want to know if the other similar 4 lights up front come on also when you activate the Multifunction switch. I worked on something similar to this recently. Mr. Sam

PS: Your issue with the radio and blower may be related, I have seen stranger things with the C5. Let's fix your light issue first and then see where we are at. Also, do you know how to use a voltmeter and ohmmeter? We will want to do some checks before we start crawling under the car.

 

Subscribed...curious on the outcome of this.

 

If you don't get an answer here, try sending your info via PM to forum member Bill Curlee. He has a wealth of knowledge on the C5 electrical system.

 

I will check that out and yes I can use a volmeter/ohmmeter. And thanks for your interest.

 

Good, post the info and then we will go from there. Most likely I will ask you to pull a rear light so we can see if voltage is getting to a running light. I will post the wire colors for you. We will use the stoplight ground wire as our ground since we know it is good.

BTW, all the rear lights go into the same single ground location.

 

Well I had a little time today to test some of what you want but......the battery is dead. Another piece to the puzzle. I charged the battery last week as it had been a month since I drove it. There is just enough charge to light the "security" light and nothing else. I will charge the battery again and check what you want tomorrow..... all good adventures start with a mystery.

 

How old is your battery? if it is old, 3 years or older, I would replace it first. I have had some really funky electrical problems that cleared up with a new battery.

 

Battery is 5 month old optima.

 

The side light don't come on and after more searching it looks like it might be my multiswitch so I'll take that apart and see if I can fix it. But I gotta be in the mood for something like that.

 

Just a little input here that may or may not help, but are well known problems having to do with the C5.

You mention that you have not driven the car in about a month. C5's have a draw on the battery due to various electronics. Were you using a battery tender?

Also, Optima batteries, while I love mine, have unique characteristics when trying to recharge a dead one. Basically you need to use a known good and well charged conventional battery in parallel with a charger to recharge an Optima completely. Supposedly, the yellow tops recover more times and more easily than the red tops.

While I made my living as a mechanic, I found that most guys shy away from electrical problems, so I made a point of getting good with electrical. A bad ground will give you very strange and seemingly unrelated problems/malfunctions. However, they are rarely unrelated when it comes to a bad ground or a marginal battery. The problem you mention with your radio and heater blower when you clutch or brake, in my opinion is very likely related to the same problem! The clutch has your safety switch which when actuated by pushing in the pedal changes the situation present and the draw on the system when depressed. The brake pedal obviously changes the draw on the system due to the draw of the brake lights.

Have you ever noticed a car on the road whose side marker lights go out when the brake lights come on? Same principal, and usually due to a bad ground.

My suggestion may be worthless, but maybe not, would be to first get a known good battery in the system and if that doesn't change anything, I would progress to checking any and all main ground points.

From there, you can begin to check the more remote and unusual possibilities (such as tearing into your multi-function switch) if you have still not remedied the original problem. Do not first suspect components which were working perfectly before the malfunction. Instead, first concentrate on known changes from the previous situation such as the dead battery. Also, a weak battery can cause ground problems as a weak battery will cause marginal connections to experience increased heat which wil exacerbate the original marginal connection condition.

Electrical trouble-shooting needs to be very systematic and definite in the results of each stage before you move on, or you will not have actually eliminated any possibilities, in which case you may as well be throwing darts in the dark for all the good it will do you.

DSTURBD

 

I do have the yellow top battery and noticed I can move the negative cable even though the bolt is tight. Feels bottomed out. I'll check that out more thorough tomorrow. I also do not have a battery tender so I will remedy that part as well. BTW I have been known to throw darts in the dark.....my neighbors hate that about me.

 

I am still waiting to see if the front lights work (refer to post #2). For your information, my FSM shows only one Multifunction output (contact, pin, wire) for all parking/side marker lights so if the fronts work then I would say the Multfunction is working.

Also don't forget to check fuse #6 in the passenger fuse box if you haven't already.

PS: I would not be so dead set to inspect the Multifunction switch before checking to see if you have voltage to at least one rear bulb. A little diagnostics can prevent a lot of wasted time.