I have an '89 auto. I am getting a taillamp failure on the car computer, but only when the headlights are on. Any ideas? Thanks,

RossD
(I noticed there is another Ross on the site, so I'll try to remember to use RossD so as not to confuse people...)

 

Ummm... this may be too obvious - but have you checked that all your side marker lights work and that you have no tail lamps out??

 

The lamp control identifies when a bulb is out (either side marker or tail) and light the warning light; when all is working correctly. If all of your lights are working correctly and you have the warning it is likely due to a poor connection at one of the bulbs. It may still light but the increased resistance is viewed the same way, try the tail lamps first because they are easier to get at.

 

My money is on the sidemarker or the license plate light bulb since I had this exact same thing happen to me.

 

The grounds for the taillamps and sidemarkers are common. Check all wires and the respective grounds for continuity.

 

The rear side-marker light housings are the first candidate for corrosion and therefore either no light or confusing the bulb computer; There are no splash guards back there pre-90.

 

Problem solved. I didn't realize side markers were included with taillamps. All four are out. Thanks for the help.

RossD

 

Ross, there are two fuses for the markers, 40 and 41 - right side and left side. The bulb on the right rear is a 'fun' because of the gas tank.

 

Mine was on the fuel pump side. What a bitch to get to. Good luck!

 

Well with all four due for replacing (unless I get lucky and its the fuses), I'm in for some FUN!!!

 

It's really not that big of a deal... just a bit time consuming. BTW, might want to check the license plate bulbs too, they are on the same circuit.

 

One other place to look if it's not the bulbs or fuses is under your tool kit. I had one wire that a PO had spliced and it came apart. I guess since it touched the body and grounded, it took that circuit with it. It didn't short the fuses or kill any bulbs, but none worked. Just a small, freaky thing that could be the cause.

 

Dave,
Are your license plate lights really on the bulb monitor?? - pretty sure that for all S4's+ they are directly driven - with no monitoring.. makes sense because they aren't so critical to safety... more of a convenience item.

On the S4's Euro's the rear fogs are not on the bulb monitor either which seems more surprising to me...?

(.... Although having lived in England and driven behind plenty of idiots with their super bright fog lights on in the rain - I' d be happy enough if they all burned out - one thing the US DOT got right IMHO! - maybe the only one...

Good for the original intent - but abused more than used...)

Alan

 

Alan, funny you should bring that up. I was told that by Susan Thomas, and I took it on faith that it was correct -- but after seeing your question, I looked at the wiring diagram, and there they are -- on their own circuit, not attached to the lamp unit at all.

I plan to change them soon, along with all rear bulbs. I'll pull one out and verify that they are truly separate.