2003 M1078A1 12v Help!

[LmtvPR]

Hey everyone, I'm a new member and have been watching this forum for years wishing to own a LMTV and I have finally made my purchase and trying to get it running properly on the island of Puerto Rico. As the title says I have a 2003 M1078A1 3126 Cat LMTV, I just got a new ECU back that had to be flashed as the old unit went bad and the truck fired right up but I have no 12v power to any lights or accessories. I have put in new batteries that are all wired correctly, my alternator is flashing both green lights for 12v and 24v. I have the battery box master disconnect on, the Master power switch near ECM diagnostic port is on and the truck starts and drives no problem. I have noticed the the master power switch on the dash does nothing when switched on and I believe its supposed to kill the truck when turned off? I have tried checking relays but the sticker on the inside panel covering my Green Power distribution panel is damaged and I have scoured the internet for a diagram with no such luck. Can someone please help me trouble shoot this as I believe the Dash master power switch is supposed to activate the 12v accessories but I could be wrong. I have no headlights, break lights, I cannot brighten or dim the panel lights and the blinkers will also not work. I do though have power to the windshield wipers which work. Any help is much appreciated.

 

[Skyhawk13205]

Hey everyone, I'm a new member and have been watching this forum for years wishing to own a LMTV and I have finally made my purchase and trying to get it running properly on the island of Puerto Rico. As the title says I have a 2003 M1078A1 3126 Cat LMTV, I just got a new ECU back that had to be flashed as the old unit went bad and the truck fired right up but I have no 12v power to any lights or accessories. I have put in new batteries that are all wired correctly, my alternator is flashing both green lights for 12v and 24v. I have the battery box master disconnect on, the Master power switch near ECM diagnostic port is on and the truck starts and drives no problem. I have noticed the the master power switch on the dash does nothing when switched on and I believe its supposed to kill the truck when turned off? I have tried checking relays but the sticker on the inside panel covering my Green Power distribution panel is damaged and I have scoured the internet for a diagram with no such luck. Can someone please help me trouble shoot this as I believe the Dash master power switch is supposed to activate the 12v accessories but I could be wrong. I have no headlights, break lights, I cannot brighten or dim the panel lights and the blinkers will also not work. I do though have power to the windshield wipers which work. Any help is much appreciated.

does your PDP have the printed circuit board?

if you do you should have LEDs for 12V battery/Ignition.

 

[NDT]

Where the battery box disconnect switch is, remove the cover, inside there are two solenoid relays, one for 12 volts and one for 24 volts. Start by checking to see if the relays are powering up and if 12 volts are going in and out of the terminals. If all is good there, next area to inspect will be the infamous LBCD box under the cab lift pump. Those get crusty connections on the terminal studs.

 

[LmtvPR]

does your PDP have the printed circuit board?

if you do you should have LEDs for 12V battery/Ignition.

Yes I have the printed broad and the lights are illuminated for both 24v and 12v power.

 

[LmtvPR]

Where the battery box disconnect switch is, remove the cover, inside there are two solenoid relays, one for 12 volts and one for 24 volts. Start by checking to see if the relays are powering up and if 12 volts are going in and out of the terminals. If all is good there, next area to inspect will be the infamous LBCD box under the cab lift pump. Those get crusty connections on the terminal studs.

I didn't have a volt meter today but will check the relays at battery box tomorrow. do you have a picture or diagram on how to exactly check the relays so I can identify what is 12v and 24v? The LBCD box, is that accessible when the spare tire is lowered? I did notice a box with cooling fins on it that had 24v and 12v labeled on it when the spare tire was lowered today to replace.

 

[NDT]

I didn't have a volt meter today but will check the relays at battery box tomorrow. do you have a picture or diagram on how to exactly check the relays so I can identify what is 12v and 24v? The LBCD box, is that accessible when the spare tire is lowered? I did notice a box with cooling fins on it that had 24v and 12v labeled on it when the spare tire was lowered today to replace.

Yes the cooling fins box is the POS LBCD. With your voltmeter, see if 24 and 12 volts are going into and out of that thing. Seach in the FMTV forum using key words “LBCD” or “LOAD BATTERY CONTROL DEVICE” etc.

 

[LmtvPR]

Yes the cooling fins box is the POS LBCD. With your voltmeter, see if 24 and 12 volts are going into and out of that thing. Seach in the FMTV forum using key words “LBCD” or “LOAD BATTERY CONTROL DEVICE” etc.

Ok I will check that tomorrow. can someone tell me exactly what the Master battery switch on dash is supposed to do because mine dosent seem to do anything? I can change the idle, disengage the fan, check the dash panel but no other switches have power. I want to check if there is a relay to that switch.

 

[Ronmar]

Just so we are not confusing anything there is a manual battery disconnect back at the batteries. There is a remote battery disconnect sw under the drivers dash, just to the left of the steering column. The main ignition switch is on the dash above the start button. There is a second remote battery disconnect ignition and starter switch inboard of the passenger tire. All the remote switches have red guard covers over them. The red remote under the drivers dash is the master and controls power to the remote disconnect and to both the dash and remote ignition switches.

Like NDT said, start at the batteries. From the batteries, the 12 and 24 passes thru the manual disconnect, then thru the disconnect solenoids, then thru the polarity/LBCD and on to power the truck. the way to test if a switch or relay is passing power is the same. set the meter for DC volts, connect the black lead to a ground point and place the positive lead on the source side of the relay (large wire on a solenoid) and you should measure the source voltage. If the relay or switch is on, and you move the red lead to the other large wire/output, you should also measure the same voltage. If you don’t the switch is not completing the circuit. The same goes for the Polarity/LBCD box. You should see voltage on the 12 and 24v input terminals and 12 and 24v on the associated output terminals.

That dash ignition switch along with the remote ignition switch inboard from the passenger tire control K1 and K2, located I believe under the power panel. Those are the 24v and 12v ignition relays respectively. Since they control ignition power when you turn off that panel ignition switch that should turn off the ignition relays and the truck should shutoff. the red switch under the drivers dash should also shut off all the power and stop the engine.

So is the remote ignition switch by the right front wheel off?

 

[Suprman]

If the truck starts and drives from the dash button you have 12 volts. The truck wont start from the push button without both voltages at the panel.