Hello, I'm new to this forum, I have had a 1988 F-150 for about 10 years. I take real good care of it and it's garaged most of the time. I converted it from 2wd to 4wd and from an auto to a 4 speed w/granny gear. Truck runs good and I enjoy driving it. it has an 18 inch steering wheel, I love it!
Anyway, I have a problem I'm hoping someone out there can help me with. About a month ago my alternator went bad, so I replaced it and decided to replace the fender mounted starter relay too, with a napa/echlin unit. The truck started ok three times after that, then right in the middle of a scrap yard scale the relay stuck and the stater would not stop trying to start the now already running engine. Well, I had to get it off the scale, starter screaming and get to the other side of the building before I could shut it down. I turned the key off, and of course it kept wanting to start. I finally found a tool in the truck to disconnect the battery, too late, burned up my starter. I checked the wire at the S terminal and it had no voltage showing with key off, and 12v when key was in start position.
I replaced the starter, some heavy wires and replaced the relay with a Advance auto "premium" unit. Hit the key, first try the relay stuck again, this time I was ready for disconnect. Both relays are stuck closed permanently, off the vehicle they are still closed. I put in an old motorcraft relay, and I am able to start the truck and disconnect the relay to starter wire too sweet, and the old relay, so far is not sticking.
Anyway, all ground are good, new in fact, and freshly tight.
I found a problem in the starter circuit. When the key is in RUN position there are 5.2 volts showing that should not be there. When the key is off, NO voltage, Key in START position, 12 volts. Key in ON engine running or not, 5.2 volts. So far I have not been able to find the source.
Here is what I've tried so far, Ignition switch test, and even though it tested ok, I replaced it, no difference. I went through the under dash wiring, connectors, and clutch switch, all working fine, but 5.2 volts everywhere. I disconnected the alternator, no change, I pulled every fuse, one at a time, no difference. Any ideas??
My next area of testing will be the ignition module, because this circuit, #32 is hooked to the EEC and the module. Any thoughts??
I do believe the relays were bad, they should have retuned to open when 12 was no longer present, but this 5.2v could keep the relay closed when in RUN position.