No starting issue

[Goliath P. Jones]

So I replaced my pcb box with a used take off unit that I bought while in the process of rebuilding my old pcb. The dash lights all come on when I operate the light dash switch. But the truck doesn't even turn over with the battery switch on and operating the ignition switch. Batteries were replaced by the last owner just before I bought the truck. The truck still started on the old pcb but dragged heavily because of my incorrect shut down procedure. I am guessing that either the take off replacement box is bad, or the starter is bad, or a combination of the two. My questions are, how do I test the pcb, how do I jump the starter(short across it)? Do I have the battery switch and ignition switch to the on position when I do? If not do I disconnect the harness to the pcb box? Can I just jump across the two large pins inside the pcb harness? I'm leaning towards it being a bad replacement box or a crapped out starter. With more towards the box being bad. Thanks for any help and suggestions.

 

[Goliath P. Jones]

Tested the batteries to be positive that they weren't down or drained. Both tested in the 12.39 range, so I am guessing that I can rule them out of the equation. I know they could be a little higher, but certainly should have enough charge to turn over the truck.

 

[simp5782]

Remove pcb harness plug. Jump the 2 large pins. This bypasses the solenoids inside

On a battery volts Is one thing. Amps Is another. They can show 12.3 but only have 400 amps rather than 850amps each. Use a load tester.

 

[Valor]

Tested the batteries to be positive that they weren't down or drained. Both tested in the 12.39 range, so I am guessing that I can rule them out of the equation. I know they could be a little higher, but certainly should have enough charge to turn over the truck.

Check out this post. Try bypassing the protective control box.

 

[Goliath P. Jones]

Remove pcb harness plug. Jump the 2 large pins. This bypasses the solenoids inside

When I jump the two large pins, would I operate the battery switch and ignition switch the same as if the pcb harness plug was hooked up? I'm assuming yes, but want to verify it before I do. As I don't want to do something that will create additional problems. Thanks.

 

[Valor]

Check out this post. Try bypassing the protective control box.

 

[Goliath P. Jones]

Remove pcb harness plug. Jump the 2 large pins. This bypasses the solenoids inside

On a battery volts Is one thing. Amps Is another. They can show 12.3 but only have 400 amps rather than 850amps each. Use a load tester.

I just bought a load tester last week, I will put it on the batteries to verify maps for sure as well. Thanks.

 

[simp5782]

When I jump the two large pins, would I operate the battery switch and ignition switch the same as if the pcb harness plug was hooked up? I'm assuming yes, but want to verify it before I do. As I don't want to do something that will create additional problems. Thanks.

Battery switch will be bypassed by doing the large pin jump. Install a 10ga wire or bigger and leave it.

Use a smaller jumper and jump from those bigger terminal to pin B. Wire tag 74. This will start the truck by doing this.

Probably a bad starter. Solenoid is drawing yop much power

 

[Goliath P. Jones]

Battery switch will be bypassed by doing the large pin jump. Install a 10ga wire or bigger and leave it.

Use a smaller jumper and jump from those bigger terminal to pin B. Wire tag 74. This will start the truck by doing this.

Probably a bad starter. Solenoid is drawing yop much power

Perfect, I'll give this a try for sure. If the truck starts with this procedure does it mean the pcb is bad then? And if not the starter is the culprit? I apologize if I am asking dumb questions, but I am wanting to be positive that I am understanding correctly.

 

[simp5782]

If your batteries are fully charged and the starter is slow then the starter is bad. These are non gear reduction starters so they do pull a lot of power.

I'll suspect a bad starter. Solenoids in the pcb are generally open or closed. Not just allowing some power thru

 

[Tow4]

If you end up pulling the starter. Remove the solenoid and disassemble it. I had a fastener come off in the solenoid on my M929. Easy fix, in my case. You can just change the solenoid if it has a lot of wear or burning on the contacts.

 

[Goliath P. Jones]

If your batteries are fully charged and the starter is slow then the starter is bad. These are non gear reduction starters so they do pull a lot of power.

I'll suspect a bad starter. Solenoids in the pcb are generally open or closed. Not just allowing some power thru

The starter was slow turning right after I did the incorrect shut down, so I replaced the pcb box. Now its not even turning over, which is why I was thinking that the pcb box was faulty. Is there still a possibility that its a bad starter or could the used pxb box be culprit? I'm going to do the jumper wire this morning to see what results that gives.

 

[Goliath P. Jones]

Okay, so I used a jumper wire on the pcb harness. Truck turns over and starts. After that I turned on the battery switch, no dash gauge lights, only when I operate the light switches do I get lights, which I know are on a separate circuit. Plugged in the pcb harness and smacked the box with a hammer, no changes in operation. Batteries tested good all around. So I am thinking that the problem is narrowing down to either a bad take off pcb box or possibly the battery switch. The fact that it semi operated on the old pcb has me leaning towards the used box I bought being faulty. Any thoughts on other culprits?

 

[Goliath P. Jones]

The truck was turned off when I operated the battery switch and the pcb harness was reinstalled.

 

[Jbulach]

Was the truck charging when you bypassed the PCB, what is your running voltage? 12.39v on poor batteries may not be enough to engage the solenoids.

 

[simp5782]

12.3v doesn't tell me anything it's a 24v system. What is the combined output voltage

 

[simp5782]

Was the truck charging when you bypassed the PCB, what is your running voltage? 12.39v on poor batteries may not be enough to engage the solenoids.

Should not be. Exciter wire has no power if he did it right

 

[Goliath P. Jones]

When I was bypassing the solenoids I had my son in the cab and asked him if it showed anything lighting up or operating on the gauges. His response was no, I didn't look myself. I'll have to check the combined output of the batteries again to see what they are, I'm guessing the procedure for this is one probe on the batteries chassis ground and one on the other on the destination hot wire that's leading to the starter?

 

[Goliath P. Jones]

Well finally it lives again. Broke down and just ordered a new pcb box from boyce equipment. Showed up in two days, swapped it in and instantly had power to the gauges with the battery switch on and started it right up. Still going to rebuild the old pcb and the used take off one that was no good. Granted they aren't giving away the new ones, but for the fact it starts and runs it's worth the coin. Lol, especially when the bed of the truck is loaded with a few ton of scrap metal.