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1971 International Truck Brake Lights

Tiny
METAPHYSICIST
  • MEMBER
  • 1971 INTERNATIONAL TRUCK
  • 175,000 MILES
The fuse for the brake lights have been blowing left and right. I can tell there's a power drain when I hit the brakes, so I know there must be a short somewhere. But, being as old as this truck is, it's a mess underside and hard to tell wires apart. I'm hoping to find a wiring diagram - at least for the brake related parts so my friend can help me [he's now wheelchair bound and so can't get under the truck. But he knows wiring pretty well].
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Saturday, June 8th, 2013 AT 3:02 PM

2 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,737 POSTS
Sorry I can't help with the diagram but a simple trick to finding a short is to replace the blown fuse with a pair of small jumper wires and 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's 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 an intermittent short you can use a stick to hold the brake pedal down while you wiggle wiring harnesses. The bulb should be off until you do something that makes the short occur, then it will flicker or get bright.
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Saturday, June 8th, 2013 AT 4:52 PM
Tiny
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Thank you! That's a great idea. Makes you wonder why such a useful tool idea hasn't been marketed yet, eh?
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Thursday, June 20th, 2013 AT 3:23 PM

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