I just bought a 1984 F150 automatic with 302. Truck drove fine until a few days ago when it had trouble starting. It sounded like a solenoid issue, giving the typical click when I turned the key. I gave the starter a few good taps to no avail. Even though headlights were bright, I charged the battery for a few hours and it started up, but the starter sounded sluggish, not like it used to.

I had the battery tested at a shop and battery and alternator were fine, both less than a year old from the looks of things. The ground cable had some corrosion so I replaced it. When I tried to ground back to the original spot on the engine block, nothing worked, so I wire brushed a spot on the frame and grounded there. After that, the truck started every once in a while, but was still sluggish.

Next, I replaced the starter. Again, it started every once in a while and did not have the oomph I expected. I replaced positive battery lead and cleaned up connections on the fender mounted starter relay. No change.

As I continued to tinker, a new problem came about. When I turned the starter, it would stay on even when I turned the key off. The starter continued to crank sluggishly until i disconnected the battery.

Another thread suggested that this could be the starter relay gone bad, so I bought and replaced the fender mounted starter relay. Now, if I turn the key the starter would stay on until I disconnected the battery, same as before, but after a couple tries with minor changes the starter spins without engaging the flywheel as soon as the battery is connected, even if there is no key in the ignition. If I pull the wires off the starter relay and put them back, I can connect the battery without the starter coming on, but as soon as I turn the key the same thing happens. I am truly stumped here. I bought what I thought were good enough parts from Advance Auto Parts. Every forum I've read suggests that the problem is related to the starter or the relay. Having replaced both, I am now completely stumped. Can anyone help? You will have my eternal gratitude.

 

You probably have a new/bad starter relay. Reading everything you should have come across a lot of people have a lot of problems with the new replacement starter relays. Just keep trying different brands till you get a good one.

You should not run your large main ground to the frame. The large wires are there for the starter motor. The starter motor is grounded/bolted to the engine block. The main ground goes to the engine. There is really no good ground from the frame to the engine, unless you have added a wire. The engine and tranny are mounted in rubber mounts, so there is no large ground from the frame to the engine. If a large ground was added from the frame to the engine, it's still not the best. That's more connections the current has to flow through to get to and from the starter motor.

 

The ground originally goes to the frame and then continues onto the starter/block, it has an eyelet in the middle of the cable. The connection is there for a reason. You probably do have a defective solenoid. Another factor can be if the battery is low or weak, the solenoid contacts can "weld" themselves together. That can also be replicated by overloading the hot side due to a bad ground.

 

bigfix
I had the same issue with my 86, i replaced the starter twice and the the starter solenoid 3 times. every time the new one would weld itself together and stay engaged. what I did was change the starter to a genuine motorcraft part ( do not buy the *#$@ Autozone or Advance sells) I also had to sand the fire wall behind the solenoid and re-drilled the screws ( they were loose) no problem since then. You may want to make sure the solenoid is properly mounted to the fire wall.

 

A bad starter (bad motor brushes, etc.) can cause the contacts in the solenoid to weld together.

If you have the original starter, the brushes might be worn down.

You MUST ground the battery to the engine.

 

It was the ground. I regrounded on the frame and the engine and the issue was solved. Old starter and relay were just fine. Thanks for the help guys.