07 Peterbilt 379 starter/relay problem

You have some thing causing the relay to stick open, thus the fusing in the open position. Wiring is my 1st guess. 2nd is ignition.

 

The starter is getting "power" from some place in the wiring going to the starter.

 

Hey do you have an Ultrashift tranny? I have had some problems like yours . I have a 05 379 C-15 Ultrashift tranny. Over the years I have had all kinds of starting problems.

 

I got the correct answer ok open your hood.. Climb up on ur driver side there will be a box little box bolted to ur firewall just under neath the window... Take that box apart... Will slide apart... Go inside ur truck and in ur fuse panel take your horn fuse and plug it in there and it will work... Got. The answer from peterbilt in missouri...hope that solves everything!

 

The horn relay behind the dash saved me some $$$ thank you.
Truck would not start but had voltage. Disconnect the starter relay, pulled the horn relay from behind the dash. Turned key and made contact with the relay and she fired up. I had to work it a bit to make it fit but the good news is that it will only fit in the right way....
Thanks for sharing this.....

 

Ive got a 2001 Pete 387 with C12. I bought it about 9 months ago. Someone put a push button next to the ignition for some reason, I found out it looked like the starter solenoid was sticking and they put that in instead of fixing the starter, it stuck a few times to where I could hear the starter spinning and disconnected the batteries and it started working right again. About a month later I started the truck in Akron, Oh to back in to the dock and I heard the starter stick and flames and smoke I could see through the hood gap. I jumped out disconnected batteries and luckily was able to get the fire out, was mainly ground wires and the wire loom. Thought I was done, had a buddy tow it to his shop just North of Pittsburgh and luckily he said it was nt as bad as it looked. The button they hooked up probably caused it along with the faulty starter or solenoid. Had the wires fixed And ECM checked along with getting rid of the button and new altenator and starter. It worked fine up until yesterday I was up around Cleveland, Oh and just got unloaded and started truck and was spinning the tires trying to get out on the ice, finally got out and was smelling something that was odd so I assumed tire or clutch maybe and didn't think anything of it. Got to shut doors and could hear the starter was spinning, hurried up and disconnected the batteries and now everytime I bump the battery cable to the batteries it archs and spins the starter motor, not kickig it in to turn the motor but just spinning the starter. Im guessing its fried now. What is it with these, this is the newer starter, I thing the M39 or T39, its the smaller one with high torque, the last one was the bigger starter. Is this the starter causing these problems or something in the truck? Seems like everything Im reading is mostly Peterbilts. Is there any way of avoiding this so the starter has no way of getting power once the engine is running? Maybe a toggle switch even after the engine is running you could switch it off and it cuts the juice in that wire while your not using it? It wouldn't be a big deal to switch it on and off, if it's possible. Sorry about the long message but the last time this happeed and I actually had fire I almost just let it cook figuring Id get another truck, luckily I didn't because my insurance (FULL COVERAGE) says that electrical fires AREN'T COVERED. That's a bunch of crap, luckily I got that out before it got bad. Any info would be appreciated.

 

electrical fires not covered?

Get another insurance company.

As for the problem, it may be a problem with the wiring harness, so have the mechanic trace the wires from the solenoid from the starter back, not the BIG wire but the small one. If he is good, he can do a couple things, one is to add a relay in between, this way you can cut the power to the small wire. Otherwise, I would get rid of the truck.

I've got a question, you did have someone look at the truck before you bought it, you did do an ecm dump and a dyno?

 

The starter you got was a high torque 39MT. These have replaced the old dinosaur 42 MT. They are much better starters. They fail less often. Nine months is not common, but it does happen. You may have a common Peterbilt 387 issue causing the starter to stay engaged after engine starts. It is the starter relay located in the upper right corner of the fuse box under the hood on passenger side. Pull it out and examine. It is probably green with corrosion. Replace it even if it is not. You are going to need another 39MT starter also. Sorry.