2002 Peterbilt C15 no crank, no start.

Here's where Im at. I'm pretty sure Ive got it narrowed down to the 2 wire harness that feeds power to the solenoid relay.

I disconnected the plug on the firewall, put my volt meter on the plug terminals that come from the + post on the battery (constant 12v) which then goes upto the relay on the firewall, which ties the signal wire from the ignition switch. No power until I move the wire around, and as soon as I let it go, I lose connection again.

Of course this simple 2 wire harness runs into the larger section of harness, which goes under the cab before coming back up the firewall and exiting. Making removing the wires a pain in the ###.

Building a new slightly shorter harness is the easiest route. Debating if Im gonna do that now or have the shop do it tomorrow while its in for an alignment.

 

Gonna keep updating this.

Shop screwed me, didnt even attempt a fix. I fixed the small harness and now have power at this plug. I can start the truck jumping those 2 wires.



That is the plug that connects the + wire off the starter, up to the firewall mounted relay, out from there and back down into that connector and down to the starter mounted solenoid relay.

Key still just clicks the firewall relay. Now, a couple of y'all said the firewall relay isn't necessary. Im hesitant to delete that though and I don't think it will solve my issue.

 

Someone tell me about the 20amp circuit breaker in the fuse panel. Mine is not popped out, but what are the chances it failed last week when I had low batteries and it wouldn't crank over?

If it failed, would it allow the firewall relay to click? Also I get zero voltage drop when turning and holding the key in the start position. So lets say right noe the batteries with the charger on them are sitting at 13v, I turn and hold the key in the start position and my factory volt meter, my aftermarket plug in volt meter/usb plug and even my phone charger that has a volt meter build in, shows zero drop in voltage. It will sit consistently at 13v.

 

And because I'm not a total ahole, I'll update this with my fix.

I picked up a 60amp push button that I was going to wire in and bypass everything just to get back on the road this week. I couldn't bring myself to rig it like that so instead of rolling out this morning I made myself keep going through the wires.

It occured to me that after I got power at the plug I posted a pic of, I pulled the firewall relay and stuck a jumper wire in the harnes. No start. Pull the plug apart, 13v on the starter side. No power at the relay side. Plug jumper wire back and reconnect plug and the truck tries to start. Heck yes. Start messing withe the plug and every time I squeezed the side with the purple/brown stripe wire, it would fire up. Took it back apart and bent the male prong up slightly and plugged it back in. Fired right off the key.

So hopefully 1 day all this helps someone else. Dont assume something is good just because. Especially if its older and electrical.