I've been doing a crime scene investigation on my 67 GTO regarding a relay on the firewall. It has three connections: 1) Ignition switch (purple wire), 2) Wire to the ignition switch post on the starter solenoid. 3) Wire to the large post on the starter solenoid (also used for the positive battery cable).  I can't find any wiring diagram for the car that includes a relay and no parts sources have anything called a starter or ignition relay for the car so it was added sometime in the past.  I understand the purpose of a relay is to open/close a circuit carrying higher amperage. Based on that I assume this relay has transferred the power load that did go through the ignition switch to the relay. Just curious to see if anyone has an idea of why it was added?

If the car was ever used for drag racing it helps to put the maximum amount of power to the starter motor.  The only reason someone would do this was to help counter act the heat soak problem that GM starter motors are prone to with headers.

I don't disagree wth notallthere's assessment. The biggest reason I have ever heard is because the car is having a hot start/heat soak issues with the starter. Due to the wrap around nature of headers or stock Pontiac performance manifolds, they tend to envelop the starter and surround it with engine heat, this saurating the starter with heat, causing it to not engage until it cools down. So a lot of drag racers (and street guys too) have used a Ford style relay system to get the relay/solenoid away from the heat to cure the problem. It is a quick fix but does not solve the real problem.

 

There are better ways to fix the problem if you are experiencing this heat soak problems. Heat sheilds, heat insulation, insure you are using a high torque starter (Pontiac had two different stock starters BTW - you want the heavy duty one) or an aftermarket mini-torque starter, and improve engine bay air flow.

 

I have also read that if your overall timing is to far advanced, you might have a problem with hot start, so try backing off your timing a couple of degrees. Personally, I have not seen this latter issue.

Thanks Mike and Frosty for the feedback. Your thoughts agree with everything I've been able to find about relays. The car starts very easily cold or hot. I have a fairly detailed history log from the previous owner, including gas fill ups, oil changes, etc. that says it had headers on it at one point and they were replaced with the original exhaust manifolds. Thanks again guys!

Talk about deja vu. I was at my local cruise on Friday night. I had the same general conversation with a guy who has a 67 Lemans with a 400 engine. He was staring at my car for a good 5 minutes before I said anything. Seems he is having the same heat soak issue. I gave him all the same tips I outlined here.