Hey!
So I have a 1978 F150 Custom, with a 302 Windsor rebuild and less than 3k on the new engine. regardless......
when I turn the ignition the starter turns over BUT DOES NOT disengage.....
so I have disconnected the battery and started with the starter solenoid......no result......still stuck.
I am looking for some direction on troubleshooting this.....
is it the starter?

Or worse electrical?
UPDATE
so disconnected the ignition module and it continued to crank when powered

 

Could be the starter solenoid is sticking, or could be a wiring fault. Try pulling the little wire off the "S" terminal while it's cranking and see if that makes a difference. If not, it's definitely the solenoid. If pulling that wire stops it, the problem is that the solenoid is still getting voltage telling it to crank.

 

Disconnect the I wire too?

Perhaps the I and S wires are mixed?

Pull both and stuff a voltmeter on it to determine which is which. With Ignition on, the I terminal wire should show around 7-9 volts. Then test the S terminal wire by having a helper switch the ignition switch to start, and it should show 12 volts.

Can't imagine the starter solenoid/relay is faulty as it would crank even if the key was in off. Perhaps consider upgrading to the newer starter solenoid/relay from a '90's truck.

 

^ This is good advice for further troubleshooting if pulling the S wire stops it when it's cranking.
It's actually a pretty common failure mode. The contacts inside the solenoid can get rotated out of position to where they're not making as good a connection and run more current through a smaller spot. When this happens, they'll kind of weld themselves together while it's on - the solenoid is initially energized by the switch, but won't let go even when switched off - but sometimes, once the battery cable is pulled or you whack the side of the solenoid with a wrench, the spring will be strong enough to pull it back open until next time.

 

The newer style starter solenoid/relay fixes this problem


from fullsizebronco.com's forum about PMGR starters

 

Hey all!
So as of today, I have swapped out the solenoid and the starter. NO RESOLUTION and again pulled the ignition module and it cranks with it uninstalled.
Full disclosure: I am just learning the in and outs of this truck and a beginner in skill. That said......
From your alls wisdom, what have I eliminated and what else should I check out?

 

Have you tried this yet?

 

hey Brian,
I assume you mean the smailer wire on the negative battery terminal?

 

On the negative battery terminal? No.

On the starter solenoid, there are two large terminals - one from the positive battery cable, and the other to the starter. There are also two small terminals - one labeled "S" and one labeled "I". The terminal labeled "S" is where the signal from the ignition switch connects to tell the solenoid to engage. The terminal labeled "I" supplies 12V to the coil during cranking.

Try removing the wire from the "S" terminal on the solenoid while it's in the runaway cranking mode, and see if it stops.

 

Roger that......
so it still cranks with the S wire detached

 

If it still cranks with the "S" wire detached, then the solenoid itself is sticking - it's unusual, but maybe the one you replaced it with was defective too.