Good batteries, no power, no lights,!

[ryanrober]

I have a 1997 M1078. It has run well for a while but has been dead for 12 months, Just have not had time to work on it. It has no lights and no power when ignition is turned on. Pretty much all functions are dead. Batteries are good. I have 12 and 24 volts to posts in PDP. I have been working through TM's, but don't seem to be getting anywhere. I have read every thread I can find, but no solutions have worked yet

Suggestions?

 

[Suprman]

Maybe a ground issue. Run a wire from the pdp ground lug to the negative on the batteries. The main grounds meet at the starter I believe. They can loosen up. You can also get corrosion on the panel contacts. Sometimes taking relays and breakers in and out can clear up contact issues. There is a dash power relay, energized with the dash switch. The vehicle lighting does not go thru this relay but there are breakers for light functions.

 

[ryanrober]

to clarify, just run a wire from PDP ground to negative on batteries and see what happens? PDP does not look super corroded. It seems like there are 2 separate systems 12 and 24 volt, neither is working

 

[Suprman]

If you loose your ground nothing will work. Are you sure your batts are good?

 

[ryanrober]

One is brand new. 2 are 2 years old. 4th is oldest but tests good. I just charged them again and hooked them back up. on PDP posts, 12 volt post reads 800 millivolts. 24 volt post reads 10 volts. Now I see the problem, any idea what it could be?

 

[Suprman]

What do they measure at the batteries? Its either connections or bad batts or the polarity box under the spare tire. You can meassure voltage in and out of the polarity box to see if its bad. You should only see around 1/3 volt drop thru it.

 

[Blairg]

What do they measure at the batteries? Its either connections or bad batts or the polarity box under the spare tire. You can meassure voltage in and out of the polarity box to see if its bad. You should only see around 1/3 volt drop thru it.

I have looked around and couldn't find a clear answer. What does the polarity box do?
Blair

 

[Suprman]

Prevents cab electronics damage when someone accidentally installs batteries backwards.

 

[coachgeo]

lights not working..... look CLOSE..... inside........ the light may not be fired up bright enough to see them actually working with out close inspection..... face to glass. If there is a smidge of light..... then they get power..... just not enough. OR pull one and actually test with a volt meter. This way your not assuming they do not work.

same for your power switch on the dash..... pull panel and test with volt meter.

also exact same thing happened to a fellow on facebook. He found a bad relay in the PDP. Get some new relays and swap them out.

 

[coachgeo]

I have looked around and couldn't find a clear answer. What does the polarity box do?
Blair

if voltage goes thru to the lugs in the PDP then doesn't that eliminate the polarity box being an issue?

have you checked voltage change at the places you have tested after switching the power button on?

 

[Ronmar]

You should see battery voltage minus 1/2V(diode loss) at the lugs in the PDP measured to ground in the PDP. If you dont have battery voltage at the test point lugs on the PDP you have a connection issue somewher between the batteries and the lugs on the PDP or ground. The wiring goes from the battery 12 and 24 outputs to the polarity box 12 and 24 batt terminals. The alternator 12 and 24V outputs are also connected here. Power flows thru a pair of diodes to the other two terminals on the polarity box which are the 12 and 24V load terminals. wires run directly from the load terminals to the 12 and 24V terminals on the left side of the PDP. Ground runs from the battery - thru a shunt resistor(to measure current) to the starter. A ground strap ties ftom starter to drivers side frame rail chassis ground. The Ground lug in the PDP connects down to/thru the floorboards on the passenger side to a strap that ties it to the passenger frame rail chassis ground(visible behind grill).

If you measure good voltage at the battery, go to the alternator and measure the 12 and 24V terminals there to ground on the frame rail. I say alternator because it is a little easier to get to than the polarity box and will also establish that power is reaching the polarity box(it must, to be measured at the alternator terminals) and you have a valid ground connection thru the frame back to the battery negative/ground point. If you dont have batt voltage there you need to determine if it is the 12/24 lines or ground. Easiest way to eliminate a ground issue is to shift your ground meter lead back to the battery - post and measure at the alternator points again. If you still dont have power you have a 12/24v line issue, most likley at teh polarity box terminals.

If you have power at the alt you can measure from the PDP 12/24V lugs using the alternator ground. If you measure good(battery) voltage at the PDP using the alt ground but not when using the PDP ground point you have a bad ground connection up to the PDP.

If you dont have battery voltage at the PDP regardless of ground used, you have a connection issue on the 12 and 24V lines, most likley at the polarity box or a bad polarity box diode. My truck started and ran fine from the day I picked it up untill about 3 weeks in. Went to start it one day, switched it on, pushed the start button and got a clunk, a click and then nothing. My 12V had disappeared at the PDP 12V lug. What I found was a corroded/dirty connection at the polarity box. Disconnected the batteries, then disconnected and cleaned all the terminal lugs on the polarity box and reconnected them which fixed the issue.

The polarity box is basically out in the weather so it gets dirty and wet every time the truck does. The easiest way to access the polarity box is to use the crane and lower the spare tire, then you can kneel where the tire sets to work on the polarity box connections.

Good Luck!

 

[Guyfang]

I am not a truck guy. But if the PDP box keeps you from damaging things when the batteries are hooked up wrong, have you triple checked to see if they are hooked up right? One of the few 1078's I ever fixed, was just that. Batteries hooked up wrong. So nothing worked. So I have to ask the question. Did you have the batteries out? Or completely unhooked?

 

[TranMan]

hey all,

Sorry ryanrober don't mean to interrupt your t/s advice from others but I to have a similar issue. Just wondering maybe it would tie into yours kind of.

Any advice would greatly be appreciated from all. So my problem I have is with an Expando Van FMTV. No Charge light comes on but once in drive it goes away, 24v gauge inop 12v gauge works, oil pressure gauge inop, temp guage inop, and speedo guage inop with the miles of the truck blinking, air gauges work fuel gauges work, trucks starts and runs fantastic even hooked up the next IQ and road tested around the yard everything shows perfect speed, voltage temp just not on gauges, the Generator regulator lights don't show and no reading on regulator 12v and 24v but the generator is showing 12v and 24v, the reverse polarity box show no light on and has voltage on both 12v and 24v checked schematics all wire and ran correctly check voltage continuity are good. What ive done so far, replaced good know polarity box, generator and regulator , gauges, data box behind the gauge, and new fresh 4 batteries with good voltage and cca. I have read on about the ctis harness tried unplugging and starting to see if it does the trick and also had read some guys picked around a pin inside on letter a and above a left side pin and still did not do the trick. My next step would be checking the pdp panel. Any suggestions and advice would be greatly appreciated and sorry again ryanrober for jumping in this thread like this but it might help both of us, maybe lol. THANK YOU!!

 

[Ronmar]

Well since yours is an A1, and your symptoms are radically different you should probably start a new thread... Then we can better advise you...

 

[TranMan]

Will Do Thank you