Coil cable failed - sources and why??

[rogerh113]

Hello,

Starting to troubleshoot my miss-fire issue, and I have found the first problem.  In replacing my dist cap and rotor, it turns out the coil cable had failed, with the connector end firmly stuck in the dist cap.  Yes, I did pull the wire by the boot.  The short 'wire' end extending out of the cap looked sort of polished, like it had been sheared / separated for a while.  Also, there is a bunch of dirt and crud in the dist cap socket - I assume with the dust cap in place, this has to be from the deterioration of the wire.  The other wires are in pristine looking shape, with no garbage in the dist cap sockets.

Two questions.

Is there a source for the coil wire only?  I tried pulling on the wire stub, but the connector is probably pretty well fused in the cap.  Also don't have any special tools for rebuilding the wire, so I assume a new wire will be necessary.  Give the condition of the other wires, I would prefer to just get the one (unless this is a sign that all are failing and due for a replacement.....)

What is likely to have happened?  Just a failed wire is not too concerning, but if this is a sign of some other coil/ballast resistor problem, then I should probably address that before frying the new wire....

Thanks -- Roger

[ja17]

Hello Roger,

Most likely you have non original carbon wires on your car. The carbon filament breaks down and then they will fail. The original wires for these cars were solid copper, tin plated,  stranded wire. These do not fail. The ends on these screw on. You can order one from one of the usual suppliers or build one yourself. If your spark plug wires are carbon wires also, they will fail in the near future.

[rogerh113]

Thanks for the heads up.  They all are the same - Beru.  Looks like it is high time for some new, old wires.

Regards -- Roger

[ja17]

Hello Roger,

Beru wires usually are solid wire. I would check them to make sure. If they have resistor ends, they can go back or become separated from the wire. Get an ohm meter and check the resistance from end to end. If you do have non solid wires, replace them.

[rogerh113]

Well, they are copper wire - I cut the cable at the end that failed.  I already ordered a replacement cable set, but will rebuild the coil cable (if possible) so that I have a good spare set.  Assuming that the end that failed was indeed a resistor, I gather that I would have to fit a resistor end to the cable to maintain proper impedence.  It will be interesting to see if there are replacement bits appropriate to the job. 

Always interesting when something like the failure of a small resistor bit hidden in a cable can bring the entire car to its knees.....

Regards -- Roger

[mdsalemi]

Another thing to keep in mind is that this wire, like the spark plug wires, carry high voltage (measured in kV).  High voltage does not always follow the rules of low voltage.

Wires routed in the wrong place; dampness, dirt, oil, grime can all contribute to the high voltage following an "unintended path" and thus provide you with a performance breakdown.

[Benz Dr.]

All '' unitended paths '' to hell are paved with good intentions.

  I remove any and all resistors on the coil wire. You want the full amount of voltage going to the distributor cap - this is very important. The rotor has 5K ohms and the plug wire ends should have 1K which is all you really need or want for this application. The resistors are there to reduce static on the AM radio band but then who listens to AM all that much any more?

[rogerh113]

Well, the new plug wires seem to have completely resolved the elusive miss-fire problem!!  It is great to have the car back on the road again.

I will put a new connector on the failed coil wire of my old set so I will have a complete spare set.  It is pretty amazing that after all this time (since the demise of AM), that wires are still produced with the resistor - both from the perspective of additional complexity (and cost) as well as an additional / undesirable failure mode.  I guess there is little time for vendors to go and rethink what they have done in the past to confirm that it still makes sense.

Thanks -- Roger