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foil wrapped wiring; what is the purpose ?
Topic Started: Apr 25 2015, 06:25 PM (1,017 Views)
Tim Keith


What is the purpose of foil wrapped wiring?

Also, when I removed the electrical tape on the wiring harness of my '96 Metro there were bare wires. What are these bare wires ?
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Good bye


Radio frequency interference, aka rfi. There should not be bare wires under electrical tape, that sounds a little after market to me.
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t3ragtop
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Turbo3 and Twincam Tweaker

some of the sensor wiring is arranged so that all the shield drains, which are bare, get joined before being attached to a common grounding point.

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Good bye


That makes sense now, thanks.
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Tim Keith


The wiring for the throttle position sensor is wrapped in blue foil. Other wiring that passes through the firewall to the ECU is bare with no insulation.

I am trying to find the source of a blown IGN fuse. I removed the engine wiring to the ECU and unwrapped and washed the oil from the wiring. Other than the bare wires which appear to have been manufactured without insulation I don't see any cause for a ignition short. I think a short *must* be in this wiring. The short began immediately after I replaced the alternator, it was tight lifting the alt through the wiring. I thought I must have cracked the brittle oil soaked insulation, but I don't see that issue.

Which wires should I target as the cause of the blown IGN fuse?

I have another '96 Metro wiring harness that I saved after I had that Metro had a blown IGN fuse. At the time I got another harness from the Pick N Pull. I know which wire on that harness is shorted. I'd rather study this problem and correct it.



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t3ragtop
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Turbo3 and Twincam Tweaker

yeah, that's pretty typical for any shielded wires in these cars. they wrapped the insulated wires they wanted to shield with foil and then used that bare wire to ground the foil to a dedicated grounding point.

check the underhood fuse and relay rack very thoroughly. pull it loose and check the steel buss bars underneath. they get hot enough to melt the plastic.
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Tim Keith


I removed the relay and under hood fuse panels. I don't see any obvious burned wiring.
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sphenicie


Tim Keith
Apr 25 2015, 07:46 PM


Which wires should I target as the cause of the blown IGN fuse?

I have another '96 Metro wiring harness that I saved after I had that Metro had a blown IGN fuse. At the time I got another harness from the Pick N Pull. I know which wire on that harness is shorted. I'd rather study this problem and correct it.






what was the issue(s) with the other harness, with the "blown IGN fuse"?

for future reference, unless you have ac and power r&p, it is easier to drop the alt out thru the bottom.

I do not have a 96 FSM but you may try to find someone who does and check there.

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Tim Keith


The other '96 wiring harness that I have kept stored in plastic bag had a short in a wire near the top of the timing belt cover.
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Tim Keith


t3ragtop
Apr 25 2015, 08:16 PM
yeah, that's pretty typical for any shielded wires in these cars. they wrapped the insulated wires they wanted to shield with foil and then used that bare wire to ground the foil to a dedicated grounding point.

check the underhood fuse and relay rack very thoroughly. pull it loose and check the steel buss bars underneath. they get hot enough to melt the plastic.
Is there a foil tape that I can use to rewrap the wires? Some of the foil came loose.

I have removed the engine compartment wiring except on the drivers side near the fuse and relays. I need to check that. Other than the foil wrapping coming loose I did not see any cause for shorts on the passenger side engine wiring.
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calrenman
Just another wrench.

The foil on my 1998 shields the upstream O2 sensor by the timing belt cover. It is shielded to keep the signal clean from RF/ radio frequency noise as stated by t3.
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punkozuna
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Do you have a wiring diagram, a Digital Volt Meter (DVM) and can you use the ohm meter on it? You'll probably need these things to track down non-obvious shorts. It can be a big pain but the basic idea is to "divide and conquer" and eliminate the good sections of the circuit until you find the short. Sometimes, using a wire to bypass parts of the circuit can help you find the bad sections.

Be glad you don't own certain late 90s German cars. They used a soy based wire insulation that is notorious for cracking after about 10 years of service. A local Euro shop mechanic I was talking to pointed out one he was working on and said the factory engine compartment wiring harness replacement was about an $8k job. OUCH!
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