Electrical Strange Wire In Harness

DuderMcMerican

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Mar 7, 2016
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Howdy,

In the process of accessing the blue fusible link that protects the eec power circuit (harness section under hood, near passenger side firewall), I discovered a strange wire in the middle of the bundle. It looks like is has (had) a delicate foil insulation surrounding it, which tore easily when separating the bundle and fully exposed bare stranded wire (please see pic.. It's the silver one in the middle with the foil shroud pulled back). I've never seen this before. Is this normal? Thanks!
 

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jrichker

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That is the TFI signal ground that runs between the TFI module on the distributor and the computer. Do your best not to damage the foil or the ground braid (if present) around the wire. The foil shield helps to protect the signal wiring to and from the TFI from all the RFI (Radio Frequency Interference) that the spark plugs and other electrical components generate. Damaged or missing foil or braid may cause the computer or TFI to see RFI and think it is part of the signal it need to function correctly.
 
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DuderMcMerican

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Oh, okay. In that case, dang. I definitely ravaged the foil pretty bad (don't think I saw a ground braid). Is there a way to fix that?

Also, why isn't the TFI signal ground also insulated with plastic sheath? It seems like a short waiting to happen should an adjacent wire's insulation be compromised..
 
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jrichker

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@DuderMcMerican

There is a way to repair the foil shield if it gets damaged. Wrap lightweight aluminum foil around the bare or damaged area, overlapping the ends over the foil shield on the wires by about 1". There is a product on eBay called "Wire Glue" ( http://rover.ebay.com/rover/1/711-5...0001&campid=5335821607&icep_item=290695765305 ).

Edit: Measure the amount of aluminum foil needed to do the job. Lay it out on the table and cut a 1" square off of the end of the foil on each side. That will leave a 1" tab of foil that you can wrap around the bare ground wire. Use some of the Wire Glue to stick it to the bare ground wire. Coat the undamaged ends of the existing foil shied with Wire Glue and then wrap the aluminum foil over it as tightly as possible without tearing either the aluminum foil or the aluminum foil shield in the wring harness. This is a job that may take some thought and practice to get it right. Try it on a wire bundle on your workbench or table before you do it with the wiring in your car.
 
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jrichker

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That would probably work ok.
The only concern that I would have is how would it hold up in an automotive environment with heat and moisture.
 

DuderMcMerican

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That is the TFI signal ground that runs between the TFI module on the distributor and the computer. Do your best not to damage the foil or the ground braid (if present) around the wire. The foil shield helps to protect the signal wiring to and from the TFI from all the RFI (Radio Frequency Interference) that the spark plugs and other electrical components generate. Damaged or missing foil or braid may cause the computer or TFI to see RFI and think it is part of the signal it need to function correctly.

I ordered the wire glue to take care of the foil insulation I boneheadedly mangled, but should I be concerned about having no ground braid or any other insulation around that wire? I was already thinking about further investigating the TFI system because of the issues I've been having with no/weak spark, hard starts when hot, and intermittent sputtering and dying, and now I'm wondering if that TFI cable's delicate shielding and lack of ground braid are suspect.. Perhaps the foil has worn away in other areas of the harness and the resulting interference is a problem?

1. Are there any diagnostics that I could perform to check the post-repair integrity of the shielded wire?

2. Should I take apart the harness from the firewall to the TFI and inspect (and perhaps reinforce the foil and/or add ground braid) just to rule it out as a contributor to my aforementioned issues?

3. Where would the ground braid ground (if I had it)?
 
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jrichker

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Use an Ohmmeter and measure the resistance of the repaired section and the joints.
Put 1 meter probe about 1" from the joint on one end and do the same thing on the other end. See what you get, the lower the resistance, the better.

Once you are satisfied with the results, leave the rest of it alone.
 
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