My truck starts itself... ...without keys

Question:

I have a 1988 F-250 with a 351 cid engine, 5-speed overdrive and 2wd. I bought this truck brand-new and have taken very good care of it. Any problems I’ve had I’ve fixed them with Ford parts and have a mechanical background.

But here’s the problem: The starter went out; I replaced it. Afterward, the truck was off, locked and I was inside the house with the keys. Then the truck started turning over by itself (luckily, it was in neutral).

So I replaced the starter, solenoid, key ignition switch (the one on the column under the dash) and replaced the starter wire. It worked fine for about eight months. Then I was inside the house, the truck was off and locked, I had the keys and it started turning over and it was in reverse! It backed up until it hit my brother’s truck behind me.

So I removed every wire off the solenoid, except for the battery and the small wire to the starter, unplugged the clutch switch, put the keys in my pocket and as soon as I touched the large gauge wire to the solenoid, it started turning and it would not shut off.

Has anyone run into this issue? It’s a permanent magnet starter but I just cannot believe it’s a starter every time.

Could my headers be heating up the starter so that hours later when it’s cooled it just starts cranking over?

Answer:

Others have experienced the same problem you have and in most instances it’s traced to a malfunctioning GEM (Generic Electronic Module). This is an electronic module that controls a wide variety of functions in your truck.

It’s located on the back of the fuse panel underneath the dash. It’s prone to corrosion so you may be able to solve the problem yourself by removing the GEM and cleaning all of its terminals.

Also, blow it out with compressed air and clean the wire terminals that attach to the GEM.