Thread: Finding a short

Originally Posted by kahlua_khan

Howdy,
I was hoping some folk on here might be able to help with a little dilemma I have with my trusty Corolla.

Whenever I switch the headlighs on I blow a fuse that controls the dash lights, tail lights, parking lights and number plate lights. There is obviously a short somewhere. I've had all the lights off and they look OK to me so I am stumped. Does anyone have any ideas as to how I can locate the exact location of the short? The best I have thought of was to test the impedance of all the lights when they are off and hopefully find one which completed a circuit (the short), but I am not even sure if this would work. Any thoughts?

Hi, does this happen when the parking lights are on or headlights. What I would do is to disconnect all the lights concerned, switch the lights on, reconnecting one at a time, till a fuse blows, that would be the section that has a short. Follow the wire back until you find the short, you may have to uncover/separate the wires to find it. When you find it, it might be melted together,or cut on a sharp edge, separate them and cover with several layers of insulation tape or heat shrink. Look in the boot for somewhere that the wire/s may have been crushed, if it happens when the parking lights are on.
Hope this helps. Let us know how you get on.
Kryn

If KBs PensNmore hints don't work, I would follow the following steps:

1. Firstly, if there is a connector for a trailer,take the socket apart and look for shorted wiring.
2. Then examine the wiring for any non-factory installations such as driving lights etc that may have been installed
3. Next, see if a wiring harness has been pinched between the engine and the body or possibly contacted the exhaust and melted. In either case you will need to cut open the harness and insulate the damaged wires.
4. Then, look for damaged wiring in the boot.
5. Next, remove and look at the light/dimmer switch for signs of electrical damage caused by a failure in the switch itself.
6. If no luck, I would then connect each individual circuit one by one to the switch until the fuse blows - you may need to do this by unplugging the harness to the switch and individually connecting each harness plug contact (except any earth contacts) to 12 volts.

Best of luck!

If you substitute a 12volt globe for the fuse it will light when the short is active.

Here's what I would do.


Get a light fitting and add two lengths of wires with a male spade terminal, this will fit modern fuse blocks. Take out the blowing fuse and insert one wire on each side of the fuse holder.

Turn on the parkers. If the light illuminates the short is on that circuit. If the light doesn't illuminate switch on the headlights. If it then illuminates you have a short in that circuit.

Shorts usually happen where a loom passes through/over/around a metal object so once the light is illuminated start jiggling/moving the appropriate harness until the light extinguishes.

Once you know where the short is you can open up the loom and look for it.

+1 on globe instead of fuse. Use a high wattage globe like a headlight or it will come on bright at low amperage.

Thanks for the responses everyone. I finally found the short, where I had crushed a wire installing a car seat. The rear light wires run straight past the anchor points.
Thanks again for the replies.