Happy New Year everyone. This question is about my 1977 F150 with 351M.

The "I" terminal on the starter solenoid keeps failing. The starter turns fine, but no voltage at the "I" terminal. This is the third solenoid with this problem.

How the heck could the "I" terminal fail? The "S" terminal is working properly, because the starter motor turns as it should.

When the key is in the "ON" position, the "I" terminal sends voltage to the coil. The test lamp shows nothing at the "I" terminal.

How can the "I" terminal fail? I don't understand that. From where does the "I" terminal receive voltage? I've suspected the ignition switch. But with the key in the "ON" position, the blower motor works, the turn signals work, all that, which leads me to believe the ignition switch is fine.

This is the third time there's been no voltage at the "I" terminal. Hmmmm......

The last time this happened, I was pulling my hair out checking and re-checking all the wiring. A neighbor insisted it was simply a faulty solenoid, and he pulled one off his back-forty 60s-something Ford pickup. I installed that solenoid, and my truck started perfectly for the past 3 months. But now the "I" terminal is dead again.

Any ideas? Where should I test next?

thanks

 

With the key in RUN, the only voltage at the I terminal would be backfeeding up the wire from the coil. if the wire is disconnected, the I terminal voltage should be 0 at all times, except during cranking. Study this:

 

Thanks a lot for that. It helps to understand how the relay works.

I didn't touch anything until this morning. Tested and got voltage at I terminal and at + side of coil. Went ahead and started it, and it did start fine.

Let it idle to replenish the batter and warm up. After 15-20 minutes it quit running.

Tested and got voltage at the I terminal, but not the + side of the coil. Had to do some other chores, so left it sit for a couple of hours.

Tested again and had voltage at + side of coil again. But it won't start.

I'll replace the coil and see if that fixes it. I don't like just throwing money at it, but the coil in it now is plenty old.

 

Replaced the Ignition Module, and now all is great!