I have a 1997 F-150 4.2L, and the starter relay fuse keeps blowing as soon as i turn the key. I have Changed the solenoid, the neutral safety switch, the ignition swith, and thinking about changing the starter. Any ideas, suggestions, experiences with this problem, are welcome with open ears. I'm fed up with this vehicle.

 

Start by disconnecting the relay and checking for grounds/shorts. then trace the wire backward to the switch checking the wire.

 

I would try disconnecting the relay and then the starter and see if the fuse still blows. Hopefully you can narrow it down that way. If the fuse still blows you'll have to start looking for wiring problems. I'd start by the fuse box under the hood. Look for rubbed, burned wiring.

 

Ok bear with me.

I'm not sure on actual names but there are wires that keep static and engine noise from coming through your radio. They can unattach from the fire wall and short out on the exaust. I dont know if this is your problem but i have heard of other people blowing fuses beacuse of these wires. Maybe someone else will have a better idea of what i'm talking about. I think the correct term is RFI maybe. Sorry about not knowing but i'm hoping it will get a response from someone who knows and point you in the right direction. Good luck

 

I dont have a wiring diagram for yours, but it's probably wired from ignition switch to anti-theft relay. If you remove the anti-theft relay does the fuse still blow?

 

Didn't exactly give enough details to work with. There are several variations.

Assuming F21 (under-dash fuse panel) is the blown fuse, an automatic transmission, and no factory Remote Anti-Theft Personality (RAP) moduule.

Power goes from ignition switch (in START) to F21 in under-dash fuse panel. From there, it goes the the Clutch Pedal Position (CPP) switch JUMPER. This is a jumper that takes the place of the CPP switch on a manual-equipped truck. From there, a split goes to the Transmission Range (TR/DTR) sensor aka Neutral Safety Switch mounted on the transmission. From there, it goes back to the starter relay mounted on the firewall.

There is no direct electrical connection from the starter motor to this circuit. The motor cannot cause this fuse to blow.

The RFI noise suppression capacitors are on the circuit that powers the ignition coils. Also, not on this circuit.

As suggested, you will need to isolate this circuit to see which part of it is shorted to ground. It is likely a chafed or damaged wire UNLESS there has been an aftermarket alarm with a starter kill option OR a starter kill switch has been installed. This is the exact circuit that either of those two items is intended to break. If either is installed, I'd check there for faulty wiring.

At the CPP, a separate circuit also goes to fuse panel where it is indicated that the circuit is only for a manual transmission. However, the wiring is in place and is another possible point of failure.

You really need the wiring diagram for this one so you can look up wire color codes and see where the circuit goes.

If you don't have either the expertise or patience to deal with finding a short circuit, take it to a technician that does.

Steve