2002 Peterbilt C15 no crank, no start.

Also I'd suggest check each battery for voltage, one could be crap. I've had that happen.

 

Completely forgot to update this. Got the truck started with the jumper wire. Went ahead and dropped it to a mechanic I use last Thurs. with a new starter because we had 4th of July plans. He said he was going to double check my ignition switch before he put the starter in, which I didn't think about. I guess I'll know tomorrow.

Those kinda got wiped out by all the rain and flooding here in the Tx hill country. My town was fine, the flooding just N of us was really, really bad.

 

Looks like its back to me diagnosing.

Starter tests good, switch tests good. Next test will be to jumper the ign switch to verify.

There is a large Bosch relay in the dash, mouted almost directly behind and above the steering column. It has a red/black wire with a tag that says "ign switch", along with a larger gauge orange wire. Can I assume that is the relay for the ignition?

 

I am the biggest idiot on the planet...

Of course there's a relay right on the firewall. Why would I even bother to look at that.

 

Update, decided to swap the old worn out ignition switch and a new firewall relay with no change other than now getting an audible click from a relay somewhere in the dash or fuse block

 

This is F'ed. I've traced out the wiring from the positive terminal on the starter where the small wire goes up to the connector, then to the relay on the firewall. Using a volt meter, I have power upto the connector that goes to the relay. Relay just clicks when turning the key or jumping power directly from the terminal to the start post on the back of the ignition switch.

Now Im starting to suspect a ground wire issue.

 

Glad you and yours are safe and mostly dry

 

Paging @Goodysnap . He might be able to help

 

The relay on the firewall is not needed with the relay on the starter your running. Just use one or the other but not both.

 

Agree with @Goodysnap, just run your signal to the firewall relay straight to the starter mounted relay. So bypass the firewall relay. If you're jumping it to that top signal, starter is good.

If you're losing that signal when you load the circuit, check for a 5 pin relay for the starter signal. Not sure if they have one or not