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Discussion Starter #1
Is there any where to get the resistor on the firewall. I believe it cuts the voltage from 12 volts to around 7 or so after things are running. Correct? Thanks again. Slime
 

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Slime, Not sure what you need it for? Any auto store will have a chrysler( pre 1971) ignition resister of which you describe. GM did not use this type of resister to cut down voltage to the coil. The resistence was built in to the wire going to the coil. Hope this helps Bill
 

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What kind of car are you needing a resistor for ?
Chevelles use a resistive wire from the bulk head connector to the coil.

GM did use the resistors in the 50's
I had one go bad on my 56 Olds, couldn't figure out why it would start and then die as soon as I let the key return to the run position. It was starting through the by pass circuit.

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Could have been that the resistor wire had already been changed to copper starnd, and the previous owner wanted to sell the car with a point distributor.

Could also be that it is from a coil that needed a second resistor loading to work right.

I have always found the 55/56/57 Chevy resistor just fine as the default resistor when there isn't a resistor wire in a vehicle, and the Chrysler resistor for a second ballast for a coil that needed one, like an Accel Super-Coil.
 

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Discussion Starter #5
Thanks for the info guys. It's a 67 chevelle. It's been a while but I was thinking that they had a resistor. It has the coil and points dist. Thanks for all the help. Slime

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Steve
 

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I hate to sound ignorant, but I am. I've never heard of this resister wire to the coil -What gauge was it? Did length and gauge determine resistance. Why is it necessary? I am installing a professionally built 505 hp 454 in my '70 chevelle SS clone; will I need to run this resister wire. Where does it come from, i.e from coil to........? Thanks for the help guys!

dave
 

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Dave, the resistor wire is needed only for points type coils. Your 70's wiring harness( if it's like my 67) will have 2 wires connecting to + coil, a yellow one that brings 12V up from the starter and a green one that is a resistance wire. I might be wrong on the colors because my 67 was converted to the HEI which uses 12V straight. I had to buy a Mallory thermal resistor ( up to 1.5 Ohm) and bolt it to my firewall. Kinda of ugly and not as clean as I'd like. If you have other questions, run a search. Lots of ignition posts floating around the site.
 

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The run side resistor wire runs through the starter motor wiring harness. The resistor wire is a special silver stranded, plastic insulated wire that has what looks like a woven cloth outer covering. Coming off the coil, this outer covering usually gets oil laden and appears to frey. On stock point coils, this wire shares a terminal with the starter energize wire, and is connected to the coil positive terminal on its terminating end.

The resistor wire is only in the engine compartment, starting at the bulkhead (firewall) connector and traveling along the firewall twords the passenger side. The wire is quite long, and travels about half way past the coil inside the loom and then doubles back to the coil.

This length is what gives the proper resistance for use with the stock point and drop-in ignitions such as PerTronix Ignitior and Mallory Unilite units and coils.

Getting the correct length to reinstall the resistor wire into your car would be easiest by simply cutting one out of an existing loom from a wrecking yard. If you must have a new one, go cut up a loom at the wrecking yard and measure the length of the one there, and duplicate it with new resistor wire from any good electronics store. You can also measure the Ohms resistance on the wrecking yard wire for the Ohms spec.

The accepted substitute is to run the ceramic ballast resistor used from 1955 through 1966 GM vehicles, all models. This resistor is mounted on the firewall on the earlier models, but can be hidden for appearance purposes. I get mine from NAPA stores, part number ICR13. Use this resistor for GM applications, not a Ford resistor, not a Mopar resistor, not an aftermarket one, this GM one or its equivelent, GM. These resistors have the proper resistance for GM stock point ignition systems. As of this day and time, the NAPA resistor is list priced at $11.49/each. Other sources may have the SAME resistor for less, do check. Last time I checked, the CORRECT resistor wire for the application was $3.50/foot, and I know the wire is at least 5 to 6 feet long.

The stock resistor wire has exactly the same resistance as the ceramic resistor gives, as it powers the same ignition system in stock form.

Yes, ceramic ballast resistors run hot to the touch, HOT, this is normal.

Of course, if your new engine is going to have an HEI or even an MSD, then no ballast resistor is required in the feed line. Use a 14 guage copper stranded wire for the feed from the same terminal the original resistor wire came from on the bulkhead connector to the ignition feed post of the unit you are using. 14 guage copper stranded wire is quite sufficient for HEI feed, 10 and 12 guage is way over-kill.

That's it in a nutshell, folks. Now, this, and the other posts, should be just about all anyone needs to know about GM ballast resistors.
 

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Discussion Starter #10
Thanks a million igition man. That was very well explained. That explains why the frayed looking wire going to the coil felt warm to the touch!! You have been a great help. Thanks again! Slime

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Steve
 

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Hey ignition man,

I want to add my thanks for the explanation of the resister wire. I will be using an HEI ignition, so I won't worry about the resistor. In the world of automotive electric, it seems like the more I learn, the less I know!! Thanks again!!

Dave
 

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Ignitionman
Since we are on the topic

I am wiring up my 72 elcamino and found a resistor or condenser looking thing with a wire coming out of it that looks like it would attach to the coil with a blade hook on the end. The condenser thing has a bolt with a nut on the other end (bottom of it) with a wire attached to it from the loom. (hope you can make since out of what I just said.


Any ideas what this is and if it goes to the negative side of the coil? Do i need it? I think it might just be an external condenser but I am not really sure.


I put in the unilite I had and the car fired without this thing attached.

Thanks
Mr. D

[This message has been edited by Mr. D (edited 12-08-99).]
 

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Mr.D, this is a noise suppressor, was initially connected to the positive side of the ignition coll to reduce the radio noise from system feedback. You really don't need it unless you hear a steady radio noise that goes up and down with the engine rpms.

In almost all cases, a good set of spiral core wires is all that is needed to eliminate the radio noise from igntiton systems, but, if it still disturbs the radio, one may be added to the positive side of the ignition coil. Use NAPA RC1, .50 microfarads.

This same noise suppressor is also used on the remote regulator alternators for the noise they can sometimes make. I've seen them on the earliest of the internal regulator alternators, too.

Rule of thumb, if it ain't broke, doesn't make radio noise, don't try to fix it with the suppressor(s).
 

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Ignition man.
Thanks for the help.

Mr. D
 

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For an historical note, I seem to remember that '58 or '59 was the last year for a resistor on the bulkhead for GM cars.
 
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