01 Peterbilt 379 Ignition Wiring Diagram

First off,,,,anybody know where I can download a Wiring Diagram for a 1999 385 Pete with a C12?

Second, having a heckuva day here,,,elecrtrical issues!! Pete 385 was having a starting issue,,,,,ie very occaisionally when you hit the key, nothing would happen, just a click once in a while,,,,sounded like the solenoid on the starter,,(I Thought),,,,,,,it happened agin the other day so while we have time I thought,,,,,lets just put in a whole new starter......great....except it didnt cure anything.........so went to testing.........clicking I was/am hearing is actually on the starter relay on the firewall....now is where it gets REAL FUN...............................without a wiring daigram I resorted to just common sense and generic heavy truck schematic,,,,,,,,,,,,I ass/u/me ed the starter relay was a main power in, main power out (the two bigger terminals) with a start terminal and ground terminal (the two smaller terminals)........batteries and cables all charged up, cleaned,,,13 plus volts at battery.............tested the little wire going to the S lug on the relay with key in START position,,,heard the click and had good volts on the litte S lug on relay,,,remember no diagram,,,,,,,anyway I somehow while ohming wires managed to accidentally touch the two little wires together while they were un hooked from the relay while the key was being held in the START position,,,,,now I have NO power in the cab when I turn key to ON position,,,no beepers,buzzers gauge lites.....and again NO WIRING DIAGRAM,,,,,,,,,,,,,,,,,,,,HOPING I blew a fuse or breaker,,but now I dont even know where to start looking???!!

HELP!!!!

THANKS

Rochester IN

we had the exact same problem in our 05 385 pete, you were correct by checking the relays on the firewall by the drivers side, I cant remember which one exactly but change out the relays and you should 1 restore power to the cab and 2 solve your starting issue. hope this helps

NW Central Ohio

...my '96 Pete has had relay issues ever since I bought it 11 years ago. I just keep bumping the start button...and eventually it pops and away it goes again. Don't know if the contacts carbon over or char or what they heck they do...but it's a little disconcerting for a minute...

SE ND

google supermiller thats a site that you should be able to get diagrams from.

Hi There. Sorry you are havin' issues. Check the relays on the lower left firewall (as I am sure you have). Thanks to Paccars never ending rule of cheapening the trucks down. The spade connectors they use are cheap as hell. The starter relay should be rather large and red or black. Also when you take the fuse/relay cover off, the placement diagram should be on the back side. When you find it? Pull it out and look at the spades to see if they are burnt. If all looks well? Then its time to go a little deeper. Pull the key switch out and check that plug for burns or carbon tracks, or melting on the back of the switch itself. Have you ever smelled plastic getting hot while running it or starting it? Another issue they have? The damn neutral switch on the tranny. I don't know if you have one but, if you do? They can be a problem. IE; you have to have the shifter in neutral with the clutch stepped out to start it. Also, this will sound kinda dumb. But, on a truck that age this could be a problem. Check you frame ground. I don't mean at the battery. I mean where it bolts to the frame. We have a few 2000 KW's that give us ground problems. Good Luck. I hope this helps.

Thanks for all the help and ideas guys!!

When I accidentily touched the two small leads while the key was in start, it grounded out and popped the 20 amp Circuit breaker below the fuse panel, so good there, just resest that. We went ahead and put a new starter relay on the firewall,,,,,,,STILL ,,,,no go,,,,,,did some more testing,,,,,turns out I was only getting 8.9 volts to the relay from the battery(actually comes from solenoid on starter where pos bat cables hook on).......the s lead from the key in the start pos was doing its job, 12.8 volts, which is what batteries tested,,,,,,,,so,,,we ohmed the wire were getting the 8.9 volts on and we were getting too much resistance,,,,,but with no diagram,,,,,we decided to run a new wire from a good power source to supply 12 plus volts to relay.,......got that goin,,,,,,STILL NO GO,,,,,,,,,,,,,,so,,,we tested the voltage at the output side of the new relay with key in start,,,12.8 volts,,,,,,,but no go,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,hmmmmmmmmmmmmmmmmm.....so I crwled underneathe and while key in start I tested the voltage to the wire going to the solenoid which came fro mthe bottom of the relay(which remember had 12.8 volts),,,,this end only showed 8.9 volts!!.................SO ran ANOTHER new wire from the bottom of the relay to the solenoid and BAZINGGA!!!!,,,,,,,,,,LIFTOFF BABY!!

Obviously we have a corroded or bad contact in a connector somewhere, but with no diagram, I AM NOT tearing into the harnesses,,,,,taped and cable tied everything up nice and pretty.....good to go!!

Thanks and I hop this can help someone in the future!!

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