The 10 amp fuse that handles the tail lights/running lights/cluster lights/rear plate lights keeps popping. The minute I turn the lights on, it blows violently. I swapped a B16 into this 94 Si last week. Everything worked fine for 1 week. I turned on the lights Saturday morning and they worked. I stopped for gas a few minutes later and they were out. They have not come back on since.

I've spent ~15 hours chasing the problem. Here's what I've done.

- Checked comination switch (lights, signals, etc). There is continuity at each pole on the swtich. I bridge the running lights with the switch out and popped the fuse. The switch is NOT the problem.

- Check cluster dimmer switch. I disconnected the swtich and was still able to blow the fuse.

- Check all bulb sockets for corrosion, water, etc. All sockets are dry and corrosion free.

- Check voltage at fuse panel. With the switch in the running lights position, I get 12.4 volts at the fuse panel. This would suggest that the problem is AFTER the panel, correct?

- Visually inspect all wires. None of the wires outside the bundle have stripped insulation or show any signs of burning, rubbing, etc. This includes white from the underhood fuse panel to the switch, red/grn from the switch to the fuse panel, red/blk from the fuse panel each lamp (red/blu for LR taillight)

- Measure resistance at each socket. At most of the sockets, I recorded 0.00 ohms of resistance. IMPORTANT!!!!!!!!!! At ALL of the sockets in the tailgate (tails and liscence plate bulbs), I recorded 0.03 ohms of resistance!!! Is this an indication that the problem may be in the tailgate???? I need to know if this is a strong indication before I cut the wire bundle open.

The car experiences no other electrical problem. Headlights, turn signals and brake lights work fine. All lighting is stock.

Thanks you for reading, I know this is long. I'm at a TOTAL loss at this point. If I take this car to a dealer and they have to being this process again, I'm looking at an astronomical labor bill that I can't afford. Your input is appreciated.

 

first off. .03ohms is a good thing. 0.00 ohms means that there is no way for your current to get to the tail lamp housings. I would suggest you start off doing two things (in what ever order you want to). 1 check for resistance from the fuse panel to switch (and also from switch to tail lamps) . 2 cehck those same cicuits if they are grounded. Sorry if this is confusing. Im trying to make this as simple as possible. Good luck.

 

I'm not good with electrical, so I'll explain how I'm getting these results.

Testing at the under dash fuse panel, grounding the black lead on my multimeter to the body, I record 0.00 ohms on the lamp side of the fuse. I get no reading on the switch side of the fuse, regardless of what positon the switch is in. Again, with the black lead grounded, I record 12.4 volts on the swtich side of the fuse panel when the switch is on.

Are you saying to check for continuity by putting one of the multimeter leads on the fuse panel and the other at the swtich, then taking a reading of resistance in the wire between the 2?

Do you mean to do the same between the fuse panel and each individual light? My multimeter leads aren't long enough.

Sorry if I'm misunderstanding.

 

Maybe if you check it a different way it'll make sense. Somewhere 'downstream' of the fuse, and 'upstream' of the bulbs; there's a wire touching ground.

Remove ALL the bulbs that are fed by that fuse, and remove the fuse itself. Now measure the resistance from the bulb-side of the fuse slot to ground. It should be OL or infinite or open circuit (however your MM displays it). I assume it will read 0 ohms, which is a short to ground. Now you just gotta locate the short. It helps if your MM has a continuity-check setting that beeps.

Unplug whatever parts of the wiring harness you can, one at a time, & check again. The idea is to narrow down the location of this short to ground. Wiring diagrams from your Helm book will help tell you where some plugs are located. If there's some way to unplug the entire back half of the car, then you can cut your detailed search in half. Get it?

Sooner or later you're gonna have to search more closely at the wires themselves. But maybe you can narrow it down to searching 6 feet of wire instead of 35 feet. The reason it costs so much for the dealer to chase it down, is it's a big tedious PITA...

 

well, you've isolated the fuse.

so take the voltmeter and continually monitor the circuit for voltage irregularities.

my hunch is a loose or wet connetor thats grounding which is shorting everything out.

the ohms wont tell you anything. what you need to look for is the voltage (amp) ratings you are getting from the wires.

 

Well, I assumed that by checking the wires for continuity, I could tell which one had a short in it. SO, last night, I made a 6 ft. test lead and tested every wire in the entire lighting system and found nothing.

I couldn't check voltage because every time I put power to the circuit, it would blow the fuse. I didn't want to apply power after the fuse panel for fear of burning up the harness.

Finally, I decided to rip the under dash fuse box out and inspect it. I began disconnecting the main wire harness segments and checking to see if the fuse would blow. With the rear main harness disconnected from the fuse panel, the lights came on and the fuse did not blow. I plugged the rear main harness in and the lights stayed on! I reinstalled the fuse panel and it's working again.

I have to assume that the short is in one of the bundles that connects to the back of the fuse panel. By pulling the fuse panel down, I separated that wire from whatever it was shorting against. Fine that the lights are working today, but now the problem is not fixed and will assuredly creep up again at the worst time.

Has anyone ever pulled the under dash harness out before? It's just too difficult to work on my back, under the dash. I can't see anything.