QuestionMy 1991 LeBaron convertible has a short in the circuit for the convertible top motor, headlights, horn and headlight door motor. I've been unable to locate a short by visual inspection. I'm baffled. The circuit will be o.k. with a new fuse sometimes for hours or days but will eventually pop the fuse. Right now the fuse pops as soon as I put in a fresh one. I know I have a serious intermittent short but can't seem to find it.This is a 40 amp fuse. I pulled out the 3 relays for the headlight door motor and pulled out the motor itself. Help!
AnswerHi Joe,
There are a couple of other circuits also connected to that fuse: fuse #21 (stop lamps) and circuit breaker #3 (power top and power seats), and either of those could be overdrawing your 40 amp fuse. Another possibility is that the wire from the blown fuse socket that goes to the relay block and those two downstream fuse sockets is shorted to ground somewhere in the pathway from the power distribution center thru the firewall and then to the relay block and fuse box.
I would suggest that you use a simple digital volt-ohmmeter to measure the resistance between various points at the fuse/relay sockets and ground; it is much more efficient and less costly in the long run than using fuses to do the tests you will need to do to find the short. If the resistance at any point is below one ohm that would be suspect of a short that is blowing the #57 (40 amp) fuse.
If the short is now present at #57 then you are in good shape to find the problem (you won't be able to easily find it if the fuse is still o.k., wait till it blows again and then be ready to test at that very moment. You can drive during the daytime without the headlight relays, but you will need the #21 fuse so your stop lights are working. You can pull the #3 circuit breaker because it doesn't affect safety. So if the #57 fuse doesn't blow under those circumstances, then the #3 circuit breaker circuit is causing the problem. If it blows, then the #21 fuse circuit is causing the problem).
Then when the fuse blows, or if it blown now, go to the #57 fuse socket and find out which clip has 12V from the battery. The other clip should read close to 0 ohms indicating a short. Then I would pull the #21 fuse and see if that causes the resistance to rise, which would tell you that the problem is in the wires from that #21 socket to the brake switch on the brake pedal mechanism. Then if that doesn't relieve the short and you haven't pulled the #3 circuit breaker then I would pull that and see if that relieves the short. If that doesn't, and you have pulled the relays and 21 and 3 and you still see a short at #57 then you have a short in the red/white wire that connects the #57 socket to the fuse block under the dash and to the relay block. So you will need to trace that wire and shake/move it to see if you can find where, when you do that, the resistance read at the pin in 57 rises way up from the low reading it has when the fuse blew.
Let me know what you find from these tests.
Roland
