Headlight switch

Tiny
NICHOLSON4
  • MEMBER
  • 1994 MITSUBISHI ECLIPSE
  • 1.8L
  • 4 CYL
  • FWD
  • MANUAL
  • 140,000 MILES
What is the easiest way to test if headlight switch is going bad? A couple weeks ago the dash lights quit, and now the park lights keep blowing the fuse. The headlights, blinkers and brake lights work just no tail lights, keeps blowing the fuse. Any ideas are appreciated.
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Sunday, February 21st, 2016 AT 10:05 PM

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Tiny
CARADIODOC
  • EXPERT
A switch will not cause fuses to blow. If it has bad contacts, which is an open circuit, no current will flow to the affected circuit, so that circuit will be dead, but no blown fuse. If a switch were to short, which basically means it is stuck turned on, the circuit would simply turn on when you don't want it to. There is no other defect causing current to be too high, so no blown fuse.

What you are describing is a short somewhere else in the circuit. For a tail light problem, look first for chewed up wires going to a trailer connector, and mangled wires in the trunk.
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Monday, February 22nd, 2016 AT 9:50 AM
Tiny
NICHOLSON4
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Thanks for the help, I will check there first.
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Monday, February 22nd, 2016 AT 10:03 AM
Tiny
NICHOLSON4
  • MEMBER
I did not find any mangled wires in the trunk. I cannot seem to trace the wires from trunk to fuse box under the hood. Would they be along the under carriage or under carpet on floor board?
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Sunday, February 28th, 2016 AT 3:30 PM
Tiny
CARADIODOC
  • EXPERT
We do not have time to follow wires until something directs us to that. Here is a copy of a better approach:

A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it is not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

For intermittent problems like yours the bulb may be dim already. Watch what takes place when it gets bright. That is when the short is occurring. It could be due to the rocking of the engine when you shift between reverse and drive. It could be due to the body flexing when you drive over bumps in the road. The bulb limits current to a safe value when the short occurs, in this case about one amp.
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Sunday, February 28th, 2016 AT 6:31 PM

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