Firewall resistor on 65

LUCKY13 · 11-29-06, 06:56 AM

I have a ceramic resistor mounted on the firewall of my 65. It looks like it needs to be replaced. Does anyone know what this resistor is for and if I can buy a new one to replace it?

cfalson · 11-29-06, 07:44 AM

It is the droping resistor for the coil, during starting (cranking) the resistor is not in the ignition circuit, during normal engine run the resistor is in the circuit, droping the voltage ~8-10 V. As far as a requirement, it depends on the coil, if you have an original or stock replacement, yes, if it's not in the circuit you will fry the coil. If it's an aftermarket that with heavier gauge wire and insulation, no.

Kid_Again · 11-29-06, 07:51 AM

Yup, agree with the assessment but why do you think it needs to be replaced? Does the car run poorly? Are the plugs wet, bad idle, etc?

You can get them at NAPA or any midyear Corvette supplier.

JohnZ · 11-29-06, 01:42 PM

Quote:

Originally Posted by LUCKY13

I have a ceramic resistor mounted on the firewall of my 65. It looks like it needs to be replaced. Does anyone know what this resistor is for and if I can buy a new one to replace it?

If it isn't working, the car won't run (it'll start, then die when you release the key back to the "on" position). If it's the original, it'll look exactly like the one in the photo below.

daryl · 12-03-06, 09:31 AM

You know it always bothers me to post, because I don’t like to have a different answer, which of course I know is right (that's is a joke) but I have seen resistors fail shorted also, not just open so the car will still run. And if the resistor is shorted or missing the points will burn up not the coil. The coil doesn't care if the resister is there or not. If you have a shop manual you should be able to look up the resistance of the resistor and take your $10.00 Sears meter and check it out to see if it is reading the correct resistance. Just my 2cents. Daryl

JohnZ · 12-03-06, 03:39 PM

Quote:

Originally Posted by daryl

I have seen resistors fail shorted also, not just open so the car will still run. And if the resistor is shorted or missing the points will burn up not the coil. The coil doesn't care if the resister is there or not.

That resistor can't fail shorted unless it's externally jumpered across the screw terminals; on the back side it has a coil of nichrome wire between the terminals, potted in a ceramic slurry, and there's no ground - the mounting bracket is attached to fiberglass.

The coil DOES care if the resistor is there or not; if it's externally jumpered (or missing entirely, giving the coil a full 12 volts), the coil WILL fry - takes a couple of hours of run time at 12 volts.

Kid_Again · 12-03-06, 05:16 PM

yup, fried a coil that way...just a few miles' run did it...you can tell by the coil being extremely HOT

daryl · 12-05-06, 12:17 PM

Boy did I ever have a senior moment. Sorry that it has taken me so long to repost. I only get on every couple of day or weeks, and usually only long enough to scan the posts. I looked up the Primary Resistance of the coil and it is only 1.0-1.13 I thought I remembered it to be higher. You are right the coil would burn up. I am still surprised the point/condenser didn’t go first. I don’t know maybe I’m still on a senior moment but I remember having problems with a shorted ballast resistor maybe it was on a Chrysler ,or AMC product or a replacement resistor not all resistors…anyway my fault. Sorry I will try and not have any more senior moments before I post again.
Daryl