Buddy bought a 91.5 W250. Drove the truck to a shop to get performance stuff done. It's been there 3 months with a mysterious wiring issue they can't solve so he brought the truck to my house.

Problem began and the shop replaced the starter.

Tried to start it and it smoked the starter relay.

New relay installed, melted wire from relay to black plug, where the wire continues down to the starter. Its the small brown wrote, not the big red one.

I cleaned all the connections for positive and grounds. All of which were lose. Battery cable were basically sitting on the post and starter wires were finger tight. Replaced the burnt wire and charged the battery. Truck cranked fine, no issues 4-5 times.

The positive cable to the starter was on bad shape so we replaced it with a new 2/0 cable. Now the problem is back. The wire from the relay jumps several inches when you inches and then smoked the new wire but didn't even turn the motor over. It acts like the battery is dead but my charger shows it at 90%.

Any ideas where to start looking? It's just throwing me off by smoking between the relay and "new" starter.

 

If the starter is immediately downstream of where the wire is melting, it tells me that the short to ground is located at, or within, the starter. I know you said that replacing the starter didn't correct the condition, but if it were me, I'd be taking apart the starter solenoid to look for somewhere that that circuit, or the winding, may be shorted or grounded. There should be a plastic sleeve insulating each terminal where they enter the solenoid's housing. Are they present and intact? I can't remember if the solenoid's winding can be removed and inspected, but if it can, you might be able to see something.

 

New starter's solenoid connector is shorted to ground.

 

That's what i was leaning towards myself. Just wanted some reassurance before spending someone else's money.

 

The shop that had the truck is kinda shady. The one and only time I stopped by there I watched the owner drill and tap both an intake and a fuel pressure port with nothing to stop the shavings from going inside the intake and IP. Both were still installed on the truck when he did it and made a comment about how it would be OK.

He can't tell me why the starter was replaced to begin with other than the truck wouldn't crank. Maybe it was bad and they got a bad one. Just hard to tell with that guy. I mean all the connections were finger tight and only two bolts holding the starter on. The guy also tried to claim he had turned the pump up until I pointed out it still had the caps on the fuel and idle screws.