M1078 LMTV will not crank

[norly99]

1997 LMTV M1078 - Hoping that someone on here can assist in identifying the problem. I have replaced the starter, the auxiliary starter solenoid, and dropped some new batteries. The switch on the dash turns everything on annd powers up. When I go to press the start button, I only hear a click near the relay but no cranking. I have also checked all fuses for resetting, but nothing seems to resolve the issue. Any ideas or suggestions would be greatly appreciated.. Kris Norlander

 

[Ronmar]

Year and model truck?

 

[norly99]

Updated initial thread with year and model…

 

[Keith Knight]

Maybe start with the starter relay.

 

[norly99]

I have swapped out relays with other capable one in the dash and still get the same result…

 

[GeneralDisorder]

Battery condition? This is almost always dead batteries.....

You need to load test each of them with them disconnected from the truck and each other.

 

[GeneralDisorder]

Jump across the auxiliary solenoid terminals and see if she cranks that way.

Also is the transmission pad lit up? Showing N?

 

[norly99]

Battery condition? This is almost always dead batteries.....

You need to load test each of them with them disconnected from the truck and each other.

2 Brand new batteries as of today…

 

[norly99]

Jump across the auxiliary solenoid terminals and see if she cranks that way.

Also is the transmission pad lit up? Showing N?

Yes…. Transmission pad does light up..

I have thought about jumping across the auxiliary…. To be truly honest have been a bit scared of the 24v…. Any suggestions to keep things relatively safe?? Lol

 

[Ronmar]

Ok, you have an A0. You need a couple specific things to come on/go click when the main switch is turned on. Oil idiot light, K11 and K24. I suspect they are because if they were not you would not be getting a click when you push the start button.

if the click you hear when pushing the button is Relay K01 in the power panel, well that tells me the trans is powering on and delivering a neutral start circuit to allow K1 to energize.

K1’s output feeds the aux start relay coil(small terminals) on the drivers frame. The other side of the coil connects to ground thru a thermal safety switch. Circuit. Some starters have a plug on the front to an internal thermal switch. Starters that don’t have this plug port have a jumper installed in the truck side wiring connector to complete the circuit to ground.

if you measure 24v on the aux start small terminals when pressing the start button, either the aux start relay is bad or that ground circuit is open…

the aux start relay of course closes the circuit to the starter solenoid to crank the starter.

as General described you can jumper across the large terminals on the aux start to crank the starter.

here is a condensed wiring diagram of the A0 start circuit…

good luck.

 

[norly99]

Ok, you have an A0. You need a couple specific things to come on/go click when the main switch is turned on. Oil idiot light, K11 and K24. I suspect they are because if they were not you would not be getting a click when you push the start button.

if the click you hear when pushing the button is Relay K01 in the power panel, well that tells me the trans is powering on and delivering a neutral start circuit to allow K1 to energize.

K1’s output feeds the aux start relay coil(small terminals) on the drivers frame. The other side of the coil connects to ground thru a thermal safety switch. Circuit. Some starters have a plug on the front to an internal thermal switch. Starters that don’t have this plug port have a jumper installed in the truck side wiring connector to complete the circuit to ground.

if you measure 24v on the aux start small terminals when pressing the start button, either the aux start relay is bad or that ground circuit is open…

the aux start relay of course closes the circuit to the starter solenoid to crank the starter.

as General described you can jumper across the large terminals on the aux start to crank the starter.

here is a condensed wiring diagram of the A0 start circuit…

good luck.

View attachment 936777

Thanks for the details…. I will give this a try in the daylight tomorrow!!

 

[Ronmar]

Yes…. Transmission pad does light up..

I have thought about jumping across the auxiliary…. To be truly honest have been a bit scared of the 24v…. Any suggestions to keep things relatively safe?? Lol

Unless you are drenched in seawater or sweat, you are going to have difficulty hurting yourself with 12 or 24v rule of thumb, never complete a circuit with any part of your body When working on ANY circuit. One hand in your pocket, other hand only touching the Plastic handle of the screwdriver. No other skin touching any other part of the vehicle. shank of screwdriver only touches the two large terminals… little spark, you know its coming, don’t flinch

 

[norly99]

Thank you sir…. Just needed some encouragement.. I hate electricity!!!

 

[GeneralDisorder]

Yeah not going to hurt yourself with 24v easily.....

The solenoid terminal jump is a quick way to rule out a lot of the high amp connections, batteries, and the starter itself. That one test rules out half the system so you can narrow your focus.