Aux Starter Solenoid Question

[chartley04]

Got a 2003 LMTV with a no crank problem. After going through everything, the problem seems to be the supply voltage coming into the aux starter solenoid isn't there. When the starter button is pressed, I got the signal voltage, and the solenoid closes like it should. I have verified the signal power from button coming into it and that the contact is indeed closing. Pretty new to working on a LMTV as it is for the fire dept I'm with. My question that I haven't found a clear answer on is where the supply voltage for the aux starter solenoid comes from? The few wiring diagrams I have manage to find makes it appear that it comes from the main power supply on the starter? I have been able to use a jumper wire to activate the starter solenoid and get it to fire but want to fix it the proper way if possible. Thanks for all the help and I apologize if this has been covered before, I did try searching but did not find the answer I'm looking for.

 

[coachgeo]

sorry no one replied. bumping this up for you.

 

[Ronmar]

OK A1
The neutral relay K26 provides power to the alt excite relay k11. the oil pressure switch provides a path to ground to energize k11 and the oil idiot light below 15PSI oil pressure. So when you turn on the ignition switch the trans should power up, both those relays and the oil idiot light must energize. k11 when energized provides power to the start switches that in turn provide power to the aux start relay on the frame rail. If k11 doesn't energize pull it and put a jumper in from pin 30 to 87(top middle to bottom middle) and see if it will crank. K11 of course provides power to enable the alternator when the engine is running/oil pressure over 15PSI. so if the truck starts and runs, you must shift the jumper to pins 30-87A, or pull it and re-install the 5 pin relay to bring the alt online...

 

[kgtgv4]

I think I am going through a similar situation with my 03 A1. I noticed it in warmer weather and the vehicle would actually crank after cooling off overnight. I have the replacement aux starter solenoid but have been waiting for it fail again before replacing it. Since installing a digital voltage reader, I notice in the colder months a massive voltage drop when turning on the ignition circuit thankfully I am still able to crank the vehicle after letting the voltage come back up.

If you're getting voltage through all the paths Ron mentioned, then it might be your aux solenoid itself.