Electrical problem on a 1990 SL
 

Help! I have a 1990 300 SL that just started blowing fuse #12 (an 8 amp fuse).This fuse powers the cigar lighter, the storage compartment light and the comfort circuitry relay term.86( which shuts down the power seats, mirrors and seat heaters even though they're on separate fuses. ) Usually the fuse blows when I back the car out of my garage and does not blow when I simply back the car up in a parking lot. (I have an electric garage door opener for what that's worth). This weekend the fuse blew when I stopped to get gasoline. Is static electricity connected with blowing fuses? I wouldn't think so. This all started after I replaced all of my fuses as a result of blowing a window fuse. Could it be the power circuitry relay? If so, where is that located?
This is driving me nuts, so any and all help will be greatly appreciated.

Bob :confused: :(

It takes quite a "short" to blow an 8 amp fuse. Static electricity cannot do this. I'd check the cigar lighter itself. There is a coil heater spring in there and it can short out. I've also found that the contacts on the fuse holders get corroded. The resistance goes up which causes heat which melts the fuse. Just a thought. Tod

Thanks Tod,

The contacts for the fuse look pretty clean, but I'll check out the coil in the lighter. I thought it looked clean. I keep my radar detector plugged in there. I've already tried unplugging that and it didn't make a difference. I just discovered another possible contributor tonight. I have car phone that I never use that apparently runs off of that fuse. I just unplugged the power cord on that.

Bob

you're on the right track
 

Sounds like it is most likely in the cigarette lighter circuitry. If need be, disconnect the lighter completely and then try it. If it doesnt blow after awhile then you know you need to replace that. If it still blows, then it is time to get yourself a wiring diagram and start troubleshooting via process of elimination. Just follow the diagram and disconnect the different components until you no longer blow the fuse. Then you know where your problem is. It would be wise to get yourself a few spare fuses for your troubleshooting.

Good luck,

I think you've already eliminated this, but not all cigar lighter plugs and sockets are compatible. The design of the socket on my wife's Peugeot is such that my phone charger plug shorts it out, and of course blows the fuse..

I remember awhile ago, I had a buddy who used to smoke and after using the cigarette lighter he would tap the lighter against the ash tray to get the ashes off it. When he would sometimes light his cigarette, some of the cigarette would stick to the filament of the lighter and he would attempt to knock it off. After doing this so many times, the lighter bean shorting out and whenever it was pushed in to heat up the coil, the coil would short to the outer shell of the lighter and blow the fuse.

Just something to think about.

Thanks FrankieZ,
This problem is so wierd. I've tried unplugging my radar detector from the lighter socket and the fuse still blew. The lighter filament looks really good. I don't think it was ever used to light a cigarette. Sometimes I can drive the car down the shore, spend three or four days and nothing happens. Then, I come home,pull my car in the garage and when I back out the fuse blows. Yesterday, I backed out of the garage, everything was still ok and when I stepped on the brake and shifited into park the fuse blew. I've tried unplugging the Radar Detector, the phone (hardwired, but on this fuse) I need help on what else to try. I don't know what stays on in the comfort circutry.

Bob

OK The common element here is backing up and or stepping on the brake. Check backup light circuit and brake light circuit. Have some watch the back end of the car while you step on the brake and shift into reverse. Corroded lamps and sockets are not uncommon. Lots of salt and water gets in there. Tod

I didn't finish my thoughts on that last post before I was called away. In the console on the shift lever is a switch which closes when you put the transmission into reverse. This switch turns on the backup lamp. If the switch is loose or the wiring around it has become worn or damaged from repeated movement, it could cause the short which is blowing the fuse. This is another case when having a wiring diagram for the vehicle could simplify the process of solving the problem. Sure wish I could find a diagram, because I'm having an electrical problem with my left window. I've tracked it down to the "rag top" controller, but I had to disassemble so much of the vehicle to trace wires out. Keep us updated. Tod