M1083A1 Electrical Maladies Starting at the Disconnect Switches

[Lugnuts]

Hello! I tried searching this and found no content as to the Disconnect Switches for the A1/ I do have wiring diagrams and that is substantial but I am looking for personal touch that you mechanics have had. I know the flaws that go with these units and know that some of you fellows do too. Recently this unit was involved with high water rescue from Hurricane Ian and now can't even be switched on to get the lights on the dash to come on. I have charged and checked the batteries. I have tested power across the Manual Disconnect Switch and it works on both 12vdc and 24vdc with no voltage drop/ The electrical master switch turns on but drops the power across the leads by 5vdc on the 24 side and 3vdc on the 12 side. I realize I have a problem with those because the batteries are showing no significant drop. I checked voltage at the Power Distribution Panel and found 4 vdc. Does the Polarity Box get bothered by water? This is an introduction and I can answer questions to what I have found/ I appreciate the assistance. Lugnuts

 

[NDT]

Have you checked the two solenoids tied in next to the master disconnect switch?

 

[Lugnuts]

Have you checked the two solenoids tied in next to the master disconnect switch?

Yes. Had what I would call a severe voltage drop. The work but on the 24vdc side it dropped it 5vdc. The 12vdc side was a 3 volt drop.
Does this system work the same as the A0's perse but on the Master disconnect does it just have manual and then the electric switch by the drivers knee. After that is it the same?

 

[NDT]

My opinion is those solenoids are damaged by salt water. Bypass them for diagnostic purposes.

 

[Ronmar]

Yep, goes from battery by cable to the manual disconnect. From there it has jumper straps to the disconnect relays, then cables from the relays to the LBCD.

You should be able to disconnect the cables coming out of the disconnect relay(closest to frame) and pull them out a bit to connect to the input terminals on the relays where the straps from the manual disconnect are attached to the relay. This will.bypass the suspect relays.

 

[Mullaney]

Hello! I tried searching this and found no content as to the Disconnect Switches for the A1/ I do have wiring diagrams and that is substantial but I am looking for personal touch that you mechanics have had. I know the flaws that go with these units and know that some of you fellows do too. Recently this unit was involved with high water rescue from Hurricane Ian and now can't even be switched on to get the lights on the dash to come on. I have charged and checked the batteries. I have tested power across the Manual Disconnect Switch and it works on both 12vdc and 24vdc with no voltage drop/ The electrical master switch turns on but drops the power across the leads by 5vdc on the 24 side and 3vdc on the 12 side. I realize I have a problem with those because the batteries are showing no significant drop. I checked voltage at the Power Distribution Panel and found 4 vdc. Does the Polarity Box get bothered by water? This is an introduction and I can answer questions to what I have found/ I appreciate the assistance. Lugnuts

.
The polarity box could also have trouble passing current if it was marginal before it got wet. No fun, but cleaning all the contacts there and in the battery box , then applying anti-oxident paste should help. Assuming that you don't have sealed batteries - salt water inside a battery is another potential place for trouble.

 

[Lugnuts]

.
The polarity box could also have trouble passing current if it was marginal before it got wet. No fun, but cleaning all the contacts there and in the battery box , then applying anti-oxident paste should help. Assuming that you don't have sealed batteries - salt water inside a battery is another potential place for trouble.

Thank you sir.

 

[Ronmar]

The polarity box itself is just diodes potted to a heat-sync. They are pretty resilient and waterproof. They are after all mounted out in the weather. Their weak link appears to be their connection lugs. They get dirty and corroded.

Now how the LBCD circuitry would fare is another story. The LBCD also has a bank of capacitors potted into the assembly to absorb the alternator surge when the LBCD disconnects the batteries. They are mounted pretty high up. If it got immersed, I would also be worried about contaminated axle and hub oil as their vents are only on the frame… There is a transmission vent on top of the transmission below where the LBCD is mounted

 

[Lugnuts]

The polarity box itself is just diodes potted to a heat-sync. They are pretty resilient and waterproof. They are after all mounted out in the weather. Their weak link appears to be their connection lugs. They get dirty and corroded.

Now how the LBCD circuitry would fare is another story. The LBCD also has a bank of capacitors potted into the assembly to absorb the alternator surge when the LBCD disconnects the batteries. They are mounted pretty high up. If it got immersed, I would also be worried about contaminated axle and hub oil as their vents are only on the frame… There is a transmission vent on top of the transmission below where the LBCD is mounted

What do the initials LBCD stand for?

 

[NDT]

Lets Be Complete Doofuses is basically what S&S and Leece Neville were thinking when they put that system on FMTVs. Load Battery Control Device

 

[Ronmar]

LBCD stands for Load & Battery Control Device.

Adding the LBCD was not when they were complete Doofuses. That came much earlier when they paired a 240AH battery bank with a 100A total current dual volt alternator. That was the root problem, the LBCD was their bandaid to keep the inevitable battery problems from eating very expensive alternators.

The doofus gene did re-emerge a little when they didn’t delete it when they fixed the root issue by shifting to a 260A alternator On the R trucks…

 

[GTUnit]

I would grab a multimeter and test the voltage at each 24V connection staring at the battery and moving one by one towards the cab. You will see where it drops off pretty clearly. Salt water causes metal oxidation so anything in contact with it will be affected to some degree. Some minor some major. Like has been mentioned you should physically clean every connection and apply grease to it even if you fond the source of the problem.

 

[Ronmar]

I would grab a multimeter and test the voltage at each 24V connection staring at the battery and moving one by one towards the cab. You will see where it drops off pretty clearly. Salt water causes metal oxidation so anything in contact with it will be affected to some degree. Some minor some major. Like has been mentioned you should physically clean every connection and apply grease to it even if you fond the source of the problem.

This test needs to be done with load applied. Resistance resists current flow, not voltage, so without current flow you can still see full voltage throughout the circuit. Like a garden hose with kinks in it, you will have full pressure at the nozzle at the end of the hose, until you open the nozzle

 

[GTUnit]

This test needs to be done with load applied. Resistance resists current flow, not voltage, so without current flow you can still see full voltage throughout the circuit. Like a garden hose with kinks in it, you will have full pressure at the nozzle at the end of the hose, until you open the nozzle

I hear you on that but he said he saw 4 volts at the PDP so if there there is enough current flow to show that kind of a drop then there is enough to do a lazy test without applying a test load. But one could easily turn on a few accessories.

 

[Ronmar]

I think that test was with ign switch on, so it was loaded...

The extension of this test is to pull full system design load thru the circuit. In a properly wired world you should see no more than 3% drop in voltage + the diode volt drop imposed by the polarity box/LBCD...

 

[Third From Texas]

When you say "high water rescues" I immediately think....

"It just stopped running for some reason"

 

[TomTime]

When you say "high water rescues" I immediately think....

"It just stopped running for some reason"



View attachment 881706

Yeah. The sad thing about it is, there were two of them at the same time. You have to wonder what they were thinking?

 

[Lugnuts]

So after working with it today, I do have power to the cab. The fault was the 24vdc disconnect switch/ I removed it, cleaned all terminals and lugs and connected straight to the Manual On-Off Disconnect Switch/ Did not have to mess with the Polarity Box although I will at a later date!
Now new problem arises/ When I turn on the Ignition Switch the Starter immediately cranks/ OK removed the wire from the Aux Solenoid and starter quit doing that/ Not the starter itself/ The Solenoid is staying activated all the time/ Remember this is an A1 and if I read my schematic correctly the Neutral Safety and Alternator Excite Relay come into action here/ Just want to verify that the push button on the dash is what is the final power going to the solenoid/ Once the engine starts and has oil pressure it disengages all power going to the starter Switch?????
I could not verify that with a running engine because the fuel system is found to be with much water. Put it this way, they had been running for several hours and when I opened the tank fill it was to the top! Hmmm. Transmission oil is white but engine had no water intrusion.
The starter switch is what I need verification on right now. New fuel filters and service right behind. Thank you Guys!

 

[NDT]

I would check out that 3 switch remote start panel in the engine compartment, maybe the switch is full of salt water allowing continuity all the time.

 

[Third From Texas]

Transmission oil is white

Ruh-roh