I just installed an anti-rot engine wiring harness on my '87 240.

After the rest of the harness was wired up, the last connection I made was to the starter solenoid. I connected the thin yellow and blue wire to the spade lug on the solenoid, and I connected the heavy red wire from the battery to the bolt connector of the solenoid.

I was a bit unsure about the medium red wire that comes out of the harness along with the yellow and blue wire, so I left this medium red wire disconnected. The car started and ran fine like this.

However I was sure that this medium red wire should also be connected to the solenoid, along with the heavy battery wire, so I connected it too.

When I went to crank the car, it made a weird "chunk" noise, so I disconnected the medium heavy red wire. The car would still crank and run, but now the battery idiot light was on and the car wasn't charging. It looks like I fried my alternator when I hooked it up this way.

WTF??? I'm really puzzled by this...

What does this medium red wire connect to and do? What went wrong here?

Any help appreciated!!!

DS