Thread: Electrical gurus help! Tail lamp fuse keeps blowing

You guys gotta help me on this. As soon as I turn on the parking lights the fuse for the tail lamps blows (10A) and my dash lights/tail lamps and everything else on that circuit goes out. I was leaving work the other day and it happened just like that. If I replace the fuse it blows instantly the first time I hit the lights. I did a pretty thorough inspection of the wiring I could see, I did not start taking apart the dash yet. Is there a common area for that circuit to short out....I am struggling here. I have not touched anything electrical in the car for months. I tryed disconnecting some of the bulbs and even disconnected some of the switches like the hazard/fog/rear defroster and the dimmer switch but the fuse still blows instantly. How do I isolate the problem, can I use the multimeter at the fuse block and at the other ends of the circuit?

you need to check your tail light bulbs. start by disconnecting everything in that circuit such as corner lights, tail lights, and marker lights. if its coming on when you turn the switch to park lights then its something in that circuit. disconect everything all at once and plug them back in one by one. once you locate the problem they go through those wires. im guessing maybe a bulb blew and shorted itself. Also being your dash lights are on that same section of the switch remove the fuse for those dash lights. i believe its a seperate fuse than the tail lamps. If the tail lamps fuse keeps blowing its more than likely on that circuit not the dash.

It could be a short in the switch causing it to draw voltage from the tail lamps to all the other accessory lights that come on when you turn your running lights on. There isnt much to the electrical system on these cars so take your time and you will find it.

You definitely have a short circuit somewhere, but the question is where? Where was the last place you were doing electrical work on your car? I would start there. Something in your parking light circuit could also be grounding straight to your chassis.

You can also do a resistance measurement from the fuse holder (fuse removed) to your battery negative or vehicle chassis on a bare metal spot (battery neg is grounded to chassis) while the switch is set to the parking lights setting.

This will tell you whether or not there is a direct ground in that circuit. Little or no resistance measure = short to ground, large or infinite measurement = no short.

that test is kind of pointless being we know he has a short. that test would only be good to just test which circuit it is that actually has the short. being its only happening with the running lights on it could be coming from the switch itself. but im thinking bulb

Oh man I feel bad for you. The above posts are right in that you have a short somewhere, but good freaking luck finding the bad boy. I had the exact same problem a few months ago. I ripped most of my dash apart, took out the back seats and trim... all for the purpose of wire chasing. This was after I had already unplugged every item on that entire circuit.. and guess what? Still shorted every time. To make it even better, what I finally resorted to after never finding the short was to literally run a new wire to all those devices and connect it up where the OEM on was after disconnecting that one. I also wired it to the headlamp switch so it all still works like normal. Also, you don't have to run it all the way back to the tails, you can just hook it up to where that harness comes up front. Magically enough, though it was a lot of work, this cured the problem. To this day I don't know WTF could have been causing the short since it was clearly not any of the devices or wiring I could see.

Not trying to scare you with my horror story . Maybe you are lucky and your short is being caused by a device, not a ghost! So definitely go into the center console and gauge cluster, and unplug all of that stuff, as well as the tail lamp harness (you can unplug that as a whole - if you pull the back seat you should be able to find the plug).

Try it then and if it still shorts, pull the headlamp switch connector and manually bridge the wires for them. If it still blows at that point then you are in for some serious wire chasing, or taking the short cut like I did (didn't feel like removing the dash!!). It can be a major PITA so just hope for the best.

Also, what car is this in? If it comes to this stage I can tell you which wires are where (if it's a B13). I'll go find the wiring diagrams I found for this and post them up for ya too. Hope yours isn't so much trouble!!!


OK Pics coming up! This is for the B13 BTW! These are the main ones I used to diagnose (or not) my problem! Good luck!

Power Scheme:


Interior Illumination:


Exterior/Tails:

Wow! Thanks for the diagrams man. As an update I took out the following bulbs: Both taillights, both combo brake/tail bulbs, front markers, and the front fogs. I turned the lights on and bam, the fuse does not blow and my dash lights came back on! So at least I know it is on one of those lines. I will now put them back in one at a time and see what happens. I had to call it quits as it is getting dark and it is freaking cold outside. I will resume battle tomorrow morning. Thanks for everyone's replies.

You are right, that test would only tell him that there is a short in the circuit. However, I would be more inclined to suspect a shorted bulb socket, not the actual bulb. A normal incandescent bulb IS a short circuit using a piece of filament shorted between the + and - polarities. The bulb only goes bad when that piece of filament breaks, turning the short into an open circuit.

Np, glad to hear your problem has already been isolated!

if you really want to get serious with it, first thing and im serious about this, take out every bulb that is part of the running lights, ex: tails, side markers, and front corner lamps. check the bulbs very very closely, you wont believe how many times ive found burnt tail light fuses due to shorted bulbs. You have to inspect the filiments carefully. if there is any sign of the filements out of place replace it. also check the trunk spoiler running light harness. from opening and closing trunk the harness can rub on the sharp edges. Next start from the back using the wiring diagram and check resisitances going to each bulb one at a time. if the resistance is high then its good, if you have no resistance to ground then you found your short. start at the farthest connector at the back of the vehicle and work your way foward so you can find the short. Do one connection at a time.

If all your stuff for those comes out fine then work at the front lights starting at the most foward connector and work your way back to the dash, if those come out good then its probably under the dash. i would say start with the easiest things first like pulling the cd player or radio and check to see if some lighting wires got pinched. then do the cluster and check the back of the cluster to see if any wires got pinched. Just think back and see if there is anything you have done recently that could have caused the problem.

Good luck. Hopefully its something simple.