How many amps is the solenoid drawing to have a 12ga wire on it?
Google suggests an SBC starter has a 10-15a draw after an initial spike of 30-50a.
So 12ga should be enough. And it was. I wired the car with a Painless harness in 2016. It was fine, until last year.
I think this wire is heat damaged. It runs from the top of the transmission (NSS is mounted on the floor shifter base), down along the case to the pan where it picks up the other 700R4 wiring and comes up the firewall. Transmission is hot. It runs past the exhaust pipe, another heat source.
From there, it crosses over the engine, along with the wiring for the oil pressure sender, distributor, carburetor choke, and A/C compressor. On the drivers side, this bundle was laying on the back of the engine. Passenger side had it secured to the firewall.
I think over time the heat got to it. The symptom is that it’ll start great when cold. When hot, the key turns and nothing happens. When cold, there is 10-11V at the S terminal while cranking. When hot, it’s around 6.5V, not enough to get the solenoid to pull in, so the starter doesn’t engage. If I connect the battery terminal directly to S with the end of a prybar, it cranks fine and starts right up. If I sit with the hood open for a while, it cools off enough to start.
I added a second wire to S, ran it inside, and used an alligator clip to connect to NSS, starts fine, hot or cold. That additional capacity, on this specific leg of the circuit, is what convinced me that this specific wire has failed. It confirms what the meter shows with voltage drops along the circuit path from battery to fuse panel to column key switch to NSS to starter S.
There’s no visible damage to this wire, I suspect that the heat damaged the copper over time. Without stripping the insulation off, I can’t see it. I may do that, once I get it all back together.
Last year, before the season ended, I added some heat shield sheathing, and pulled the harness up off the engine on the drivers side. In re-running this circuit, I’ll put the shielding stuff back on, and secure the harness off the engine. I’m also going to step it up to 10ga. This circuit runs in some hot places, I can’t change that, so I’m thinking that the additional capacity of the larger gauge wire can only help with any heat related degradation.
Only time will prove me right or wrong on this one. I think I’m right. But I’m doing Power Tour in a couple of weeks. That should provide some nice hot driving conditions to prove it. I’ll bring my jumper wire and my prybar just in case.