What wire actually activates the solenoid? From PCM or the other one?

 

The PCM sends ground to the solenoid to activate it.

 

The PCM uses the Brown w/ Red Stripe to activate the glow plug relay. The PCM grounds that wire out thus causing the glow plug relay to activate.

 

So why do I get 12v with key on? It should be 0 if it is a ground, right? And this is with it off the solenoid.

 

On the brown/red wire or the red/green?

 

I tested red/green. I assumed that is what activates it,

 

You assumed wrong. I guess you completely forgot to look at the post above where I said it was the Brown w/ Red Stripe wire that activates the glow plug relay

The Brown w/ Red Stripe will have 12v on it until the PCM grounds it out, then it will have 0v and it will ohm to ground.

 

I did read what you wrote, and my reply was if PCM wire goes to ground, then why would I read 12v from it when disconnected. If it goes to ground then it should be 0v.

 

You will read 12v on the Brown w/ Red stripe wire when the PCM isn't grounding the wire.