Fuse 12 Keeps Blowing in my 89 560SL!

[sshankman]

I hope someone can give me advice here, because I'm not sure what to do.

A little background: My 560 has been out of service for about 6 months, as I took my sweet time installing new leather and a new top, and having my wheels powder coated (look great, by the way). During that time, it was started and moved around occasionally, but not enough, as when the job was finally complete, the battery was dead. I jumped it a few times, but no matter how long I drove, it still wouldn't start without a jump. I put a new battery in, and it worked great.

Next, I noticed that the clock stopped working. When the radio wouldn't turn on, I figured it was a fuse. Sure enough, number 12 (white, 8 amp) was blown. As i inserted a new one, there was a spark and the new one blew immediately. Just for fun, i tried a red 16 amp fuse and it didn't blow, but when it went in, i heard a relay click and the ignition buzzer went on, as if the keys were in the ignition (they weren't). I removed the 16 amp after the test.

I have a feeling that this problem is correlated to the recent battery change, but I have no clue what the relationship could be. There's a short someplace. My research on this forum found that it could be the radio, but this wasn't happening before the battery change, and throughout the 6 month reconditioning period, the radio and associated wiring was untouched.

any ideas?

[8092400e]

Check the dash wiring for mice! It apparently happened to my 88 before I bought it. I have documentation for a $1200.00 repair to replace a mouse chewed harness that was effecting everything from turn signals to the radio.

Just a thought, after 6 mos of sitting, mice get comfortable.

[sshankman]

I pulled the radio, no evidence of any mouse bites in there on the wiring, and I even disconnected all the wiring, and pulled the radio out. I guess there could be a damaged harness someplace, but i have no clue where to even start looking.

Short of going thru every item controlled by that fuse, is there any other way to diagnose this? Does anyone know of any device that can help pinpoint the short, or at least allow me to continue to test without going thru a hundred little white fuses? the only way I can test it now is to install a new fuse and watch it spark and blow.

Thanks.

[dpetryk]

You need a schematic for the circuits associated with the problem fuse. Disconnect all of the devices on that circuit and install the fuse. Then reconnect each device one by one and keep an eye on the fuse. When it blows you have the offender. If it blows with all the loads disconnected the problem is most likely in the wiring harness. I have made a fuse replacement device that uses a circuit breaker (aircraft type) set at 5 amps. I had to make it myself to find a problem exactly like yours. This procedure usually helps if you have some knowledge about electricity or electronics and how the wiring in the car is routed.

What devices are powered by fuse #12?

[sshankman]

It's fuse #12, 8 amp. Here's what it controls:

Diagnostic
Trunk light
roof light
entrance light
hazard warning system
warning monitor term. 5
autom. antenna
electron. radio

It will be easy to disconnect the lights, hazard switch, radio, and antenna (from the radio), but what about the "diagnostic" and "warning monitor term. 5"?

[neds380sl]

SS- A suggestion: never , even for fun, install a fuse that is rated higher than that prescribed. Bad idea. For the rest, I'd get a multimeter and begin checking all of those things hooked to your fuse. It's tough, but you'll eventually hit the dead short, which is probably what you have. Might be a wire with the insulation rubbed (or bitten?) through.
Ned

[GSMITH]

I would suspect you did something around the seats when you replace the leather. The seat belt warning lines maybe??? I am talking about the one that plugs in under the drivers seat.