Intermittent short: How do you find those?

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david58
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Intermittent short: How do you find those?

Post by david58 »

Victor H wrote:I have an intermittent short that I just can't seem to find. Happens randomly while driving, I can hear the arc or snap and then the fuse goes. No relation to turning, turn signal use, brakes, stopping, starting etc. Sometimes when sitting at a light, "click" and fuse pops, othertimes driving down the road. Can't go more than 15 miles without using a fuse. Also, I never use the wipers or headlights.

Here's the set up. '61 bug, converted to 12 volt. No radio. It's always the first fuse in the box (the one that's hot when ignition is on), the left hand one nearest the steering column. That circuit has my oil pressure gauge, tachometer, fuel pump and in the engine compartment, that wire goes to a relay with direct power from the voltage regulator to run my electronic ignition & coil. All the gauges otherwise work normally.

What approach would you suggest? Should I disconnect one thing at a time and see if that does it? Is there any way to wire in an amp meter and see if something is spiking the voltage? Any ideas appreciated.
The Noof wrote:Easiest way is process of elimination:disconnect evrything related to that fuse, one circuit at a time untill the fuse failure stops.Leave only whats neccessary to keep the ignition/charging system active.
Marc wrote:Yes...and that's way more stuff than I'd ever put on the same fuse.
In this case I'd first put the ignition/gauges, fuel pump, and wipers/t'signals/brakelamps on three separate circuits and if the problem persists start isolation from there.
Note that if the park switch in the wiper motor is broken it can cause mysterious intermittent shorts - there's power going there when the wiper switch is "off".
This is from this thread.
http://www.shoptalkforums.com/viewtopic.php?t=103713
fortyeye
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Joined: Thu Apr 01, 2004 1:49 pm

Post by fortyeye »

I'm with Marc on this one. Could be too much draw on the fuse. The combination of multiple loads on the same circuit with the added resistance of poor connections (anywhere in the circuit-especially at the fuse block itself) can overcome the puny fuses in a stock VW electrical layout. The answer isn't a larger fuse ... it's diversity. Split those loads up on more than one circuit fed by more than one fuse. If you suspect a fault in the wiring (a ground ... not an intermittent short) then I prefer to troubleshoot with an analog meter on an unpowered circuit. Take the fuse out and disconnect the loads. Look at just the wiring with your volt/ohm meter. Using an analog ohm meter makes hi resistance grounds (and intermittent faults) easier to find. Old wiring, poor connections, and possible insulation breakdown (possible ground or cross) could be causing the fuse to blow.
AKA clearsurf
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