[roger1]

Originally Posted by dataway

Boy when you look over the electrical system in a 68 GTO it's easy to see where about 3 relays would have made the system so much less likely to burn down.
I was just restoring the console harness and wondered about the big thick purple wires to the neutral switch .. yep, it's feeding a huge load from the battery to the neutral switch, to the ignition switch to the solenoid.
I noticed the purple wires had seen too much heat, I assume someone laying on the starter for two minutes overheated them. A relay on the firewall and they could have removed six feet of voltage sucking wire and a couple of high current connections.
Same with the headlights of course. At least they used one for the blower motor ... but then they also feed all that current through a cheesy speed switch on the dash.
I would have much rather had to replace a relay now and then than have critical circuits sending all that juice through a maze of wiring.

It was a very popular thing to do to add a relay to help with voltage drop on the purple wire. It was even suggested in a GM tech bulletin. The thing you saw done was to use a Ford solenoid for the relay.
However, even that is a band-aid approach to what is the real problem which is the basic design of the GM starter/solenoid and they way they routed the wires to it without enough heat protection.

This is the best explanation I have come across that explains how a GM starter/solenoid works.

https://autosystempro.com/starter-co...it-components/

Notice that the solenoid has 2 windings in it. One to pull-in the plunger and one to hold it in place once it has been pulled in.

Also notice that the ground for the pull-in winding goes through the windings in the starter. This part of the design is why this starter is so prone to a no-start malfunction caused by heat soak.
This is also why a adding a relay or solenoid is a band-aid at best because you are trying to overcome a high resistance ground problem with lowering the voltage drop on the positive wire. However, it can make the problem better and why it has been done.

The best way to solve the problem the problem today is to go to a mini starter. The solenoid will draw much less current and a relay isn't needed. The size makes it a lot easier to protect the wires from heat too. New wires have much better quality insulation on them than they used 50 years ago too as long as you buy high-quality automotive wires.