I have an 86 Ford F150 302. She was running great yesterday morning. I started and stopped her three or four times running errands around town. Later in the afternoon the starter was cranking slow and unable to turn the engine over to start.

I had the starter tested at the parts store. It was working, but a couple of the guys said it was spinning slow and didn't look like it was working correctly so I bought a new one.

Immediately after installing the new starter she fired right up with the old solenoid installed. I shut her off and tried to start her again, but the slow cranking issue was happening again and she wouldn't start.

I assumed it was the old solenoid so I replaced it, but this didn't help. The starter did the slow crank a couple times and then I heard clicking.

Just to make sure I didn't get a lemon solenoid, I bought another (different brand), but this one is the worst. It doesn't do the slow crank or clicking. Just a low humming type sound when I try to start the truck.

Any ideas of what might be happening and what I can do to troubleshoot/fix this issue?

 

I'd get the battery and alternator tested and clean all terminals.

 

The battery is fairly new. If the battery is good and fully charged, and the alternator is bad, would the truck fail to start?

 

You need to do a load test on both the battery and the alternator. Parts stores can do this in the parking lot.

I would take apart all connections and clean them, both power and ground.

 

Don't ASSUME that your battery and ground cables are good. Check your battery voltage at the starter terminal and the ground on the starter body WHILE attempting to crank and see what the voltage is.

Also did all three starter relays come from the same source? If so it's entirely possible that EVERYONE one of them is bad. MOST rebuilt auto parts are not tested by the remanufacturer and in a LOT of cases their rebuilt procedure is just plain ****. Long story but years ago I had this problem with MOPAR starters that were ALL rebuilt by the same large rebuilder in Roanoke and I eventually had to rebuild the starters myself to get them to work properly.