Truck won’t start and transmission pad not lighting up

[BrooklynnMasonry]

The pdp is the circuit board breaker relay panel on 3126 trucks. Feel it see if sockets are loose in the board. Visually inspect. A bad board usually causes odd intermittent issues. The wtec3 tcm is a common failure. Keypads go bad too water drips down onto them over time and gets in.

Ok, that’s how we were able to start it by jumping the relay I’ll blow the dust out today and check it out!

 

[Suprman]

You can also jump the large relay on the inside of the drivers frame rail to crank. Your issue sounds like a keypad or tcm issue. You can take the keypad out and open it up see if its wet.

 

[BrooklynnMasonry]

You can also jump the large relay on the inside of the drivers frame rail to crank. Your issue sounds like a keypad or tcm issue. You can take the keypad out and open it up see if its wet.

The key pad does look like there’s moisture under the screen! Thank you so much for the help!

 

[Suprman]

Take it out and open it up. A wet wtec3 keypad can put the truck into drive on its own. I would replace it. There’s nothing special about the keypad its the same civilian wtec3 type.

 

[BrooklynnMasonry]

Take it out and open it up. A wet wtec3 keypad can put the truck into drive on its own. I would replace it. There’s nothing special about the keypad its the same civilian wtec3 type.

I will get one

 

[abfisher1798]

The pdp is the circuit board breaker relay panel on 3126 trucks. Feel it see if sockets are loose in the board. Visually inspect. A bad board usually causes odd intermittent issues. The wtec3 tcm is a common failure. Keypads go bad too water drips down onto them over time and gets in.

My 8088A1 has an electrical issue. I flip the battery disconnect to ON and measure with a voltmeter the starter solenoid and the 12v and 24v posts on the PDP. All initially show full voltage, then slowly drops at .1 volts per second, bottoms out around 9.5v, meanwhile the batteries are full at 25v.
No power to the instrument panel either, except for the instrument lights. The only power I can push through the cab are the headlights, turn signals and hazards. Nothing else, including the WTEC.

 

[Suprman]

I would start by adding a large ground wire from the batts negative to the main frame rail. Then check the connections on the polarity box its under the spare tire.

 

[Ronmar]

My 8088A1 has an electrical issue. I flip the battery disconnect to ON and measure with a voltmeter the starter solenoid and the 12v and 24v posts on the PDP. All initially show full voltage, then slowly drops at .1 volts per second, bottoms out around 9.5v, meanwhile the batteries are full at 25v.
No power to the instrument panel either, except for the instrument lights. The only power I can push through the cab are the headlights, turn signals and hazards. Nothing else, including the WTEC.

Inboard of the spare tire is the polarity protection device, or in your case it is called the LBCD. The battery power flows thru the manual disconnect, thru the remote disconnect(large relays) and to the LBCD. At the LBCD input it splits to the alternator. The LBCD has 2 large diode banks in it which prevent batteries connected incorrectly from killing the controllers and other electricals. The relays are controlled by those remote switches (under cab and under drivers dash) and by the LBCD if it detects alternator overload(keeps a bad oversized battery bank from killing the alternator).

what I suspect you are experiencing is a bad connection or relay contactor, probably on the 24v leg, somewhere along it’s path since you get 12v lights.

Voltage is only valid when tested under load... you can get full voltage fed thru a high resistance circuit throughout the circuit when unloaded But try and pull current thru that high resistance and the voltage will fall on it’s nose...

The first problem I experienced on my truck besides the ones it came with, was a fail to start shortly after I got my truck home. Would push the button and get a series of clicks. Had 12 and 24 at the PDP test points until I pushed the start button, then the 12V went to near zero and pulsed as the relays clicked. This turned out to be a badly corroded connection at the polarity box. Once I cleaned that up, voltage while cranking hardly differed from that measured at the batteries.

I suspect you have a similar issue and you need to measured loaded voltage along the circuit path from the batteries to PDP, to see where it is falling off. I mentioned the LBCD as located where it is between tire and air cleaner, it is out in the weather and subject to increased corrosion potential...

 

[abfisher1798]

Inboard of the spare tire is the polarity protection device, or in your case it is called the LBCD. The battery power flows thru the manual disconnect, thru the remote disconnect(large relays) and to the LBCD. At the LBCD input it splits to the alternator. The LBCD has 2 large diode banks in it which prevent batteries connected incorrectly from killing the controllers and other electricals. The relays are controlled by those remote switches (under cab and under drivers dash) and by the LBCD if it detects alternator overload(keeps a bad oversized battery bank from killing the alternator).

what I suspect you are experiencing is a bad connection or relay contactor, probably on the 24v leg, somewhere along it’s path since you get 12v lights.

Voltage is only valid when tested under load... you can get full voltage fed thru a high resistance circuit throughout the circuit when unloaded But try and pull current thru that high resistance and the voltage will fall on it’s nose...

The first problem I experienced on my truck besides the ones it came with, was a fail to start shortly after I got my truck home. Would push the button and get a series of clicks. Had 12 and 24 at the PDP test points until I pushed the start button, then the 12V went to near zero and pulsed as the relays clicked. This turned out to be a badly corroded connection at the polarity box. Once I cleaned that up, voltage while cranking hardly differed from that measured at the batteries.

I suspect you have a similar issue and you need to measured loaded voltage along the circuit path from the batteries to PDP, to see where it is falling off. I mentioned the LBCD as located where it is between tire and air cleaner, it is out in the weather and subject to increased corrosion potential...

View attachment 834804

Thanks very much! That gave me a place to start.

 

[Lugnuts]

Gentlemen, I'll dare to enter into the fray. Real life experience in short, I started truck, went to put in gear. Nothing. Shut off tp reset computers. Wouldn't start. Transmission shift pad did not light up but mode button made mode come on. By pass start it and it wouldn't shift. I ran PDP because power was not hitting neutral notification. It acted most like it had a bad ground. So after 3 weeks of PDP, wiring, etc, I was able to swap keypad out with known good and lo and behold trouble went away. That's my story and I'm sticking to it.