So I've been chasing down a starter heat soak issue on my 1981 C3 with a starter heat soak issue, cleaning all cable contact points, testing different components, replaced ignition switch, Replaced Starter Harness, and noting voltages and different points of connectivity during testing.

Testing results starting with fully charged battery
All continuity checks normal
Battery at rest- 12.5v to 12.6v
Battery while engine running 14.20 (see notes below, now alternator issues after this initial test?)
Battery Positive to various Negative cable grounding - Frame back crossmember 12.54v, Engine Large Neg engine cable both contact points 12.5v, at starter 12.5v, at alternator positive 12-5v, at starter harness to engine block harness 12.5v
Tested Purple ignition wire along path got 12.5v
Tested Purple wire when cranking 8.9V
Tested Purple wire disconnected from starter 12.3v

I did find the front frame to motor Negative cable a little crusty and stiff, I cleaned it up and I'll replace that eventually, but for now saw no voltage drops at those connection points. I'm going to check the Amperage at the wire and few other places when I get my higher Amperage DC meter, Clamp meter ordered and on the way for testing. But other cables all looked good for a 43 year old car.

So from all the testing I was leaning at possibly changing out the starter with the same type large OEM GM or go with a mini-starter. Before replacing though I thought I might take the solenoid off the starter to check for wear and possibly clean up and flip the contact points and disc around to use the none wear clean areas. I've done this before and saw many had success online.

Yesterday I took the starter out, cleaned up the solenoid, flipped the contact point over to the unworn areas and reinstalled. The car started up faster than ever before and I tested cranking it over with cold starts and hot starts multiple times, so far that worked during testing.

After testing though I noticed the Choke Light staying on, Voltage meter reading low with the car off and key on, and also low Voltage reading while the car was running. I tested with my multi-meter at the battery with the car running and found only 11.75 volts and not charging. I went back around testing all connections to make sure they were connected correctly, for tightness and saw 12.5v at all locations when car turned off, even at the Bat terminal at the Alternator, I knew the battery was at a good charge level.

I did notice about a week ago while driving on the highway my voltmeter dipped below 12 volts for a while then jumped back up over 13. My next step today will be testing for voltage while the car is running at the alternator BAT Terminal to see if it shows charging.

Didn't give it any thought at the time, but do you think the alternator was going bad this whole time and periodically failing?

Does anyone know how to test the alternator on the car to see if it is bad before pulling it out and replacing?

There is another plug in on the alternator with 2 connection points. Reading the Shop Manual it looks like one (Brown) shoots low voltage signal to the Choke Relay, there is also a 20amp Choke Heater Fuse I need to check and from reading the manual if either loses power from the alternator it causes the Choke Light to remain on. The other wire (RED) connects to the solenoid and used for the control circuit.

Thank you

 

Check voltage while running at BAT terminal of alternator and on the white plug the number 2 wire, probably red, both should show 13.5 to 14.5 volts.
Does the starter solenoid have a heat shield?

 

Thank you, I will check those locations for voltage today and let you know. No I have no heat shield on the starter solenoid.

 

I just checked the voltages again.
- Battery was charged full 12.5v
- At Battery while running the car, turned on lights and the heat/AC blower is constantly running as usual on low speed and got 12v after using some to crank a few times etc.
- At Alternator BAT and number 2 RED connection I got 12v
- Check again at both Battery and Alternator and it ran down to 11.85v
- So it looks like the Alternator is not charging the system.

Dang!

 

Definitely sounds like alternator has failed since you don't see the minimum 13.5 at alternator.

 

Thanks again MelWff. I ordered an alternator and picking it up after work today. Delco-Remy Reman like the one I had, but this one come with a lifetime warranty at Oreilly's. I got one for our Pontiac Vibe GT two years ago at Oreilly's as well with lifetime warranty and it's still going strong. I'll let you know how things turn out.

 

Make sure the alternator is clocked correctly. In other words the plug with two wires on the back half of the alternator is in the same position relative to the front half of alternator's mounting holes as your current alternator. This link explains clocking.
https://bzerob.com/library/gm/gm-altpartno.html

 

Picked up the alternator last evening. Clocking is the same, but the pulley was not the correct size, when doing a preliminary install the belt did not sit fully in the pully groove correctly, it stuck out 3/16" outside above the pulley. I read online this is sometimes an issue with replacement or remanufactured alternators due to being built and adapted for multiple applications. Reading the application information again on Oreilly's site, it says "Optional; Pulley Change May Be Required". I went back to the store and they removed the original fan, spacer, pulley, washer and nut for me. I removed the installed pulley and reinstalled the original. I found a good thread here on the forum with input from Lars on how to remove the pulley nut and reinstall the nut with an impact, https://www.corvetteforum.com/forums...y-removal.html . The direction he gave worked like a charm. I'll complete the alternator install and connections this evening and post how all turns out.

 

New Alternator installed, looks like everything is working again.
With the car off
Battery Voltage 12.6
Voltage at BAT on Alternator 12.6
Battery Voltage at Starter RED cables 12.6
Battery Voltage taken from RED Starter Cables connected to Solenoid stud and frame grounds 12.6

With car running
Battery voltage reading 14.65
Voltage at BAT on Alternator 14.65
Volt meter happy again running normal readings
Choke Light is now off

Thanks you for your help MelWff