Hey everyone. So my husband and I have changed his starter and selenoid on the side wheel well on his 87 f150 lariat about 4 times since may. The selenoid keeps frying and now his truck won't stop trying to turn over unless you unhook the battery cable. We went through this before but don'tdon't get why it keeps happening. It made a weird noise before it happened this time. Does anyone have advice? We need it running again asap.asap.

 

Most of the time it is caused by a low or bad battery. When the battery is low the voltage is down and that means the current is up to do the same work. More current will weld the contacts closed in the starter relay and cause this to happen.

 

Our battery is new but someone told us it may be to small. Could that be a possibility? Its a 5.0 same as a mustang. Do you have advice on how many crank amps We need?

 

That could be if it is too small but I dough it as the small battery would be able to to put out enough amps to weld it.
I would think at least 650.
The engine may also be very hard to turn while cranking.
Does it crank slow?

 

It cranks slow when he's been driving it all day. In the morning it cranks and turns off and cranks up again and stays running. We just bought a new solenoid were gonna put on when we get home and see what it does.

 

Slow cranking is a current with a lot of amps.

 

He changed the solenoid and it cranked up for him. We gotta see how its getting too many amps like you said though.

 

Your problem sounds like it could easily be a bad starter. I've seen them wear out the motor brushes in the starter, and still work, but it cooks the solenoid beside the battery.

 

We changed the starter 4 times since may. I hope its not the starter again

 

It's not "getting too many amps"

The starter needs 'X' power to turn the truck over.
Power (watts) is voltage times amps.
If the voltage getting through is low, the current (amps) will be high, to meet the demand of the starter.

Too much current (amps) will overheat the contacts of the solenoid, causing them to melt and stick together.

My advice?
Check, clean and tighten all connections at both ends of both battery cables.
And both ends of the starter cable.
Replace any cable that looks at all questionable.

Cranking slow at the end of a day of driving could (and likely does) mean that heat soak is causing high resistance in the starter itself.
This is much more common with headers than manifolds.

 

The Made In China Junk and/or Made in Drug Cartel Run Mexico solenoids being dumped in this country of recent are GARBAGE -- evidence the fact you've replaced these and the starter four times...............

Something is "sticking" in your ignition circuit and the probabilities are high it's that solenoid you've replaced repeatedly (what we call a "plunger" hang internally)........the other candidate is surprisingly your alternator -- could be shorting internally and playing with the battery terminal on the solenoid (starter relay)-- getting errant current at the solenoid----a "field" here can move that plunger in your solenoid and keep that starter circuit sticking.....

 

From a point of electromotive physics this is absolutely impossible.
From the perspective of someone who has been dealing with various charging circuits for 40 years there is no evidence.

 

X2 ^^^^
There is no way an alternator can do that if you can make heads or tails out of the broken sentences. I am not even sure what he said.

 

thank you for the advice its running for now but if it happens again he's gonna check the starter cable and change it out again

 

The resistance could be anywhere in the circuit.

Check the battery negative cable to the engine block.
This connection is pretty much out of sight so it often gets ignored.

Good luck, it must be frustrating.
Welcome to the forum!