Coil Resistance Wire Question

[Doug Flaten]

I posted this question in a thread that is getting pretty old. Maybe Jack or one of our other electrical experts can shed some more light on this.

I have always wondered if there was anything special about the coil resistance wires. Were they just of a certain gauge and length such that they had more resistance in a circuit where you might normally run a bigger wire? Or were they of a specific construction or something that created a specific resistance?
Thanks,
Doug

[Terry M.]

???? for Bill Clupper or Jack Humphrey ??? *TL*

Doug,
I too think it is special wire. IIRC it is solid, but all the other wires are stranded. I thought the different insulation was for the higher heat that results from its resistance. Being solid, and stiffer than the usual automotive wire, I too thought some special connecting means might be necessary.
Bill Clupper or Jack Humphrey are the folks with the real poop, rather than my guesses.

[Clem Z.]

Re: ???? for Bill Clupper or Jack Humphrey ???

the resistance wire is made from nichrome not copper.

[Mike M.]

Re: ???? for Bill Clupper or Jack Humphrey ???

tery: ht e ac delco 12 ga fusible link cable i'm holding in my hand, part # 6293923, is mulifiliment, not a single wire but it is stiffer than regular 12 ga wire. mike

[Clem Z.]

Re: ???? for Bill Clupper or Jack Humphrey ???

a fuseabe link is not the same as the resistor wire used to lower the voltage to the ignition coil. the fuseable link is a "fuse",it melts when there is a short in the wiring harness so the whole harness does not go up in smoke.

[Mike M.]

Re: ???? for Bill Clupper or Jack Humphrey ???

thanks for the enlightment, clem. regards, mike

[Jack H.]

Re: ???? for Bill Clupper or Jack Humphrey ???

Clem's got it right.... They simply used a conductor other than copper whose resistance (guage of wire + length) was a 'known'. If you 'chop' into an old TI wiring harness, you should find one of the wires (solid core) with a handy emboss in its insulation that reads something like this: "Resistance wire -- DO NOT CUT/SPLICE".

The specifics of the wire's core material (might be nichrome, could be aluminum) wasn't important. What was important was the wire's ability to handle the current load AND exibit the required resistance in the run length available to that section of the harness. It was a GREAT idea! It eliminated the need for a discrete, heat belching, ballast resistor and basically generated a 'distributed' resistor.

Other methods of achieving controlled resistance within the wiring harness are the use of different lengths of specific copper joined with crimp connectors strategically located to 'control' the end-to-end resistance of a given run. Ever spend time tracing a Chevy wiring diagram to find a simple point-to-point run changes color code and wiring gauge for 'no apparant' reason?

This is a means of introducing controlled resistance and this can also be done to critically dampen wiring runs that switch loads (turn on/off) to thwart transient response ('ringing') which might interfere with the intended switching function (the transmission line effect; EE 305 course)....

[Kurt B.]

Re: ???? for Bill Clupper or Jack Humphrey ???

Jack,
I know nothing about auto electronics so forgive this question if it sounds dumb: are you saying that I can not splice in a piece of resistor wire.
This all started becasue my 68 has a piece of wire going from the harness to the coil that looks like it is not correct (was poorly spliced) and then I learned from this discussion board that I should be using resistance wire of 20 gauge with red, white, black color code.
How do I go about fixing this problem without replacing the entire engine harness, or don't I? I have no other electrical problems, (or didn't when I started this resto 6 years ago).
Thank you,
Kurt Bunting # 26406

[Jack H.]

Re: ???? for Bill Clupper or Jack Humphrey ???

Read again, Kurt.... I quoted what you'd expect to find on the insulation of a mid-year TI harness inside the tape wrap. This is just ONE form of resistance wire and I gave several examples of where/why resistance wires are used. Nowhere did I say what you could or couldn't do with your personal car....

Obviously, the reason one would put such a note as I described inside the harness, is to warn the average 'bubba' mechanic he's about to get in over his head. When you cut/splice, WHAT is the resistance profile of your splice? When you cut, does the donor wire you're cutting have the same resistance/linear foot as what you're replacing? If you can't answer these questions, then you can only hope to get 'close' to the factory original resistance profile of your original harness.

In some applications, close is good enough. In others (like thwarting ground plane ressonance and critically dampening transmission lines), close isn't good enough and being off can result in circuit performance side effects.

For the resistance wire used in non-ballast cars, there are two consequences to being off the money: (1) you've got too much resistance and you run 'cold' spark across the board, (2) you've got too little resistance and you run 'hot' spark and shorten the life of your coil. Some of these orignal coils run as much as the $100-200 amount you'd pay for a fresh/correct ignition harness, but, hey, you CAN go cut and splice....

[William C.]

Re: ???? for Bill Clupper or Jack Humphrey ???

Sorry to get into this late, but I was away watching the (delayed) NHRA Nationals in Indy. Jack is correct in that the resistance wire to the coil is made of a resistive core. There were a couple of different versions thru the rears, the earlier version being a multiple-strand construction with a rubber insulation and a braided cover over the rubber. They were cut to a specific resistance value as specified by the customer (Chevrolet) and the excess was folded back into the wiring harness with a rubber sleeve places over the end of the loop. Later versions used the Nichrome single conductor version jack described, I think these were brown with a white stripe, but I can chack for sure if it is omportant to anyone.

[Terry M.]

Question is.... *TL*

Can this resistance wire be spliced, or does the whole length need to be replaced? If it can be spliced - recommended technique? The original post was also looking for original appearing wire to replace about a foot that had broken off and a previous repair was made with standard wire.

[Clem Z.]

Re: Question is....

a T&B(thomas and betts) crimper and the proper connectors(sta-kon) should do the trick. the T&B crimper makes a "U" type crimp not the flat type like most auto parts crimpers. anytime you use a T&B type crimper make sure that the "split" in the connector is not where the male part of the crimper make the indent as it will cause the connector to split open.