Electrical Issues

[boquinc]

Good afternoon,

I have been following a few threads in the rebuild of the PCB. I have done this and the only way to continue to start the truck is to jump it. Previously to me the N-Safety switch was rewired and everything in the TM says to replace the PCB leading to the rebuild. With power on only I can get nothing, with run/start switch I get nothing. The only time I get anything is with the jumper in and power on all the warnings come to life and then I can jump the starter and the truck runs. What am I missing?

 

[ericp351]

Hello . If I follow- you have a jumper at N. Start Switch, and jump 24 volts to starter to crank. If so- sounds like 2 troubles. 1- screwed up N S W as you probably knew, and 2.- you need to trace hot and ground from the batts to, then thru your bat switch- then in and out of your start switch until trouble found. Jumping from main bat ground to engine block would quickly find any "earth" fault. Please advise if mis under stood. Do you have headlights?

 

[boquinc]

Hello . If I follow- you have a jumper at N. Start Switch, and jump 24 volts to starter to crank. If so- sounds like 2 troubles. 1- screwed up N S W as you probably knew, and 2.- you need to trace hot and ground from the batts to, then thru your bat switch- then in and out of your start switch until trouble found. Jumping from main bat ground to engine block would quickly find any "earth" fault. Please advise if mis under stood. Do you have headlights?

No jumper at N start witch just the jumper on the PCB harness wire between C & D....I do have headlights.

 

[ericp351]

No jumper at N start witch just the jumper on the PCB harness wire between C & D....I do have headlights.

Sounds like your batteries, cables, and grounds are all ok. Starter also. I'd look to the start switch, at least until an electrician can chime-in. I'd work it vigorously and give it a rap with a hammer handle before you open or remove it. Little down side. Good Luck.

 

[Jbulach]

Good afternoon,

I have been following a few threads in the rebuild of the PCB. I have done this and the only way to continue to start the truck is to jump it. Previously to me the N-Safety switch was rewired and everything in the TM says to replace the PCB leading to the rebuild. With power on only I can get nothing, with run/start switch I get nothing. The only time I get anything is with the jumper in and power on all the warnings come to life and then I can jump the starter and the truck runs. What am I missing?

What truck are we working on, and does it have an engine over temp light in the dash behind the steering wheel?

 

[boquinc]

What truck are we working on, and does it have an engine over temp light in the dash behind the steering wheel?

M939 dump is the truck type and yes it has a temp light behind the steering wheel.

 

[Jbulach]

So guessing a M929 or M929A1… disregard the question about the over temp light, I miss-remembered it being tied into the PCB.

Not sure if I’m quite following your post, but you have to jumper the C&D terminals in the cannon plug for the PCB, then jumper the starter solenoid and the truck will crank and start? Do you have 24v power at terminal A in the cannon plug when your battery switch on the dash is on?

 

[boquinc]

So guessing a M929 or M929A1… disregard the question about the over temp light, I miss-remembered it being tied into the PCB.

Not sure if I’m quite following your post, but you have to jumper the C&D terminals in the cannon plug for the PCB, then jumper the starter solenoid and the truck will crank and start? Do you have 24v power at terminal A in the cannon plug when your battery switch on the dash is on?

Yes.

 

[boquinc]

Rebuilt the PCB after following the test procedure and still having trouble getting the truck to start with switches.
-Switch on I get 12V on the bottom right small lug
-Have constant 24V on the big bottom right lug.
-Neutral Safety switch test good.
-TM test procedure Starter Motor inoperative; No Solenoid Thump pg2-109 leads to replace PCB again.
I'm located in ENC so if anyone has any ideas I'm all ears.

 

[Jbulach]

So your problem should be the bottom solenoid or associated wiring in the PCB, or the PCB itself is not getting ground.
I’m not seeing the wire on the terminal In circled in yellow, it should be going to ground.

 

[Jbulach]

Rebuilt the PCB after following the test procedure and still having trouble getting the truck to start with switches.
-Switch on I get 12V on the bottom right small lug
-Have constant 24V on the big bottom right lug.
-Neutral Safety switch test good.
-TM test procedure Starter Motor inoperative; No Solenoid Thump pg2-109 leads to replace PCB again.
I'm located in ENC so if anyone has any ideas I'm all ears.
View attachment 916697

Sorry, forgot to hit reply so you have a better chance of getting a notification.

 

[boquinc]

So your problem should be the bottom solenoid or associated wiring in the PCB, or the PCB itself is not getting ground.View attachment 916703
I’m not seeing the wire on the terminal In circled in yellow, it should be going to ground.

Okay previously there was no ground there. So thank you. This has been an inherited project.

 

[Jbulach]

It was probably a tiny diode what “went away” when something was connected wrong.

 

[boquinc]

It was probably a tiny diode what “went away” when something was connected wrong.

So just run a small wire to ground from the terminal without the diode?

 

[Jbulach]

So just run a small wire to ground from the terminal without the diode?

Yes

 

[boquinc]

Yes

That fixed it! Thank you for the help.