Welding wire can handle the amps
It was a 1973 Chevy pickup. It was a last year of the points style ignition and coil.
I decided to replace the distributor and coil with an electronic GM HEI distributor.
I got it for a discount from a friend that had a automotive repair shop.
It arrived the day before mother's day and I spent an hour installing it and setting the ignition timing.
What I paid for the distributor I asked the guy about the size of the wire going to the coil or hot side of the distributor. I knew the HEI distributors had a much hotter coil.
I told him I was running up to my mother's house in Vancouver about 250 mi away the next day.
He replied for something like, just hook up the old coil wire and you should be fine for something temporary.
The old coil wire seemed pretty tiny..... Maybe 16 gauge? ...18 gauge?
I decided, rather than to risk running this hotter coil through the ignition switch that I would just wire it directly to the battery and add a rocker switch inside the cab for this trip. This was just going to get me up to my moms place and back home so it was temporary wiring.
I think I decided on running a 14 gauge wire directly from the battery to a bus block installed on the firewall. From there I ran another 14 gauge wire across the firewall and into the cab then connected it to a rocker switch which was just going to lay on the floor for the duration. From the switch, the wire ran back out to the firewall and over to the coil.
From these wires that ran from the battery to the switch and back across to the ignition coil, I'd estimate about 15 ft of 14 gauge wire.
I put a few wraps of electrical tape around the wires, to temporarily connect them with the wire harness. I taped the wires just to neaten things up for the trip.
Anyway the rocker switch work fine and I did a few test runs through town to check the ignition timing and make sure everything ran well and it did. The truck started quicker and ran an idled smoother....... It was 9:00 p.m. so I had successfully installed the distributor and went to bed.
The next morning my brother and I headed out of town and once we got on the interstate 5 we were doing fine. My rocker switch was a lighted yellow switch. I was in the left lane and as I was moving to the right lane on the highway the engine lost power.
I glanced at the switch and it was no longer lit up. At that very moment, smoke started pouring out of the windshield defroster vents....... and I'm talking white smoke
I immediately continued across the right lane into the shoulder which was gravel and skidded to a stop as fast as I could. I popped the hood open and I grabbed the wiring that I had connected to the bus bar on the firewall and gave it a hard jerk.
That brand new 14 gauge wire was now almost bare wire with plastic dripping off of it.
Long story short.......... and yes it was a long one
I discovered that the HEI coil drew a lot more amperage than the old coil in my 73 pickup. With a run of wire that long, even stepping up a gauge to 14 could not handle the current.
Okay now I am stranded along side of the freeway with the hood up and no more smoke. I stripped the wires off the bus bar then twisted the ends together. Those two short wire ends would complete the ignition to the coil as long as it hadn't been damaged.
I hopped back inside twisted the ignition key and the engine came back to life. 100 miles later, I had to stop and get gas
I pulled into the gas station, got out, lifted my hood, and untwisted the wires on the bus bar to turn off the engine.
There's a NAPA parts store next door so I went over and bought another switch and some 12 gauge wire. So this temporary fix worked just fine.
I made it home and redid the entire wiring the 12 gauge wire. I installed a rocker switch in the dashboard. All that wire did was turn on the ignition. If you put the key in and twisted it the engine would crank but it would not start till you flip the ignition switch.
I just left it that way as a bit of a theft deterrent.