Weird electrical problem

[Ang2gna]

Grounds and batteries clean, good, and tight. Batteries at 25.5volts. 1987 6.5 na that went to Maine in 2006 for rebuild. I replaced the 60 amp with a 200 about 2 months ago and everything's fine. Today I went to start and the light blinked once and then no power. None at all when I turn the switch to run or start. I have read the glow plug gospel thread and can't seem to find help there. I have the white label (I think natron) S3. I have 24 volts at starter and 24 volts at gen. I checked for voltage at the top pcb connection and the middle hole has 23 volts. I can't read the numbers or letters to tell you what the hole is labeled. After connecting the plug I disconnected the negative battery again and pulled the bottom pcb plug. After re connecting the batteries one of the bottom right pins on the box was reading 23 volts. Again I couldn't read what pin it was on the connector. The other ones were reading 0. No lights work and neither will the heater. The weird thing is that I have 24 volt lights in the back that I turn on with an aftermarket toggle. It is hooked up with a 30 amp fuse. They won't turn on either and the fuse is fine. I even tried taking that connector off the batteries to see if that was the problem and it wasn't. Since that connection won't work it leads me to believe that it is a battery problem, but seeing they are reading fine and putting out power to the starter and gen I don't think it is the batteries. I've looked at the schematics in the tm but I don't know how to read them. Maybe someone can help me there. Thanks for all your help. You guys are great!


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[NDT]

Try turning on your aftermarket lights and then measure the voltage at the starter connection. If it's now zero, you have a battery cable ring terminal connection that is internally corroded between the terminal and the copper cable and not allowing big power through. It's a bit of a goose chase, but you should be able to find it.

 

[Action]

Seems folks often have electrical problems after adding things to the system....
The heater won't work until the engine is hot. Did you mean the fan?

 

[Ang2gna]

Try turning on your aftermarket lights and then measure the voltage at the starter connection. If it's now zero, you have a battery cable ring terminal connection that is internally corroded between the terminal and the copper cable and not allowing big power through. It's a bit of a goose chase, but you should be able to find it.

I did as requested and it did register 0.00. So what ring terminal should I look at? For a goose chase you sure were spot on lol.


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[Ang2gna]

Seems folks often have electrical problems after adding things to the system....
The heater won't work until the engine is hot. Did you mean the fan?

Yes Action. The fan. It was a simple hookup right to the positive stud of the battery. I hooked in an inline 30 amp fuse. I didn't touch any of the hmmwv wiring. The weird thing is that the aux lights won't turn on even they are on their own toggle and the fuse is good. It's hooked right up to the battery. I can't wrap my mind around why even those lights won't turn on if the batteries are good.


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[Action]

what are the aux lights grounded to?

 

[Ang2gna]

what are the aux lights grounded to?

I have to check where I grounded them tomorrow, but the problem persists even when I disconnect the aux lights from the battery and connect the batteries as per the tm.


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[NDT]

I did as requested and it did register 0.00. So what ring terminal should I look at? For a goose chase you sure were spot on lol.


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All of them. Negative cable to shunt, shunt to ground, battery interconnection, positive to starter.

 

[Ang2gna]

All of them. Negative cable to shunt, shunt to ground, battery interconnection, positive to starter.

Thanks. I am looking at the condition of the actual cords themselves right? I understand they could be internally corroded and I may not be able to tell other than cutting the covers off. I guess I could just replace one at a time until I find the bad one. Also could it be the shunt itself?


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[NDT]

Try this method. Turn on your aftermarket lights. Put one probe of your voltmeter on the 24 volt positive battery terminal. Place the other probe on the positive battery terminal of the other battery. Should read 12 volts, if not, the battery interconnect cable is faulty. Next, while leaving the first probe on the 24 volt positive terminal, place the other probe on the shunt. Should read 24 volts. If not, the cable between the negative battery terminal and the shunt is faulty. Lastly, place the second probe on chassis ground. If you don't get 24 volts, the cable between the shunt and chassis is faulty. I think that cable ends on the starter.


See if you can look at the cable strands in the ring terminal without cutting off the shrink sleeve. If you see crusty crap in there, that is the problem.

 

[Retiredwarhorses]

Grounds and batteries clean, good, and tight. Batteries at 25.5volts. 1987 6.5 na that went to Maine in 2006 for rebuild. I replaced the 60 amp with a 200 about 2 months ago and everything's fine. Today I went to start and the light blinked once and then no power. None at all when I turn the switch to run or start. I have read the glow plug gospel thread and can't seem to find help there. I have the white label (I think natron) S3. I have 24 volts at starter and 24 volts at gen. I checked for voltage at the top pcb connection and the middle hole has 23 volts. I can't read the numbers or letters to tell you what the hole is labeled. After connecting the plug I disconnected the negative battery again and pulled the bottom pcb plug. After re connecting the batteries one of the bottom right pins on the box was reading 23 volts. Again I couldn't read what pin it was on the connector. The other ones were reading 0. No lights work and neither will the heater. The weird thing is that I have 24 volt lights in the back that I turn on with an aftermarket toggle. It is hooked up with a 30 amp fuse. They won't turn on either and the fuse is fine. I even tried taking that connector off the batteries to see if that was the problem and it wasn't. Since that connection won't work it leads me to believe that it is a battery problem, but seeing they are reading fine and putting out power to the starter and gen I don't think it is the batteries. I've looked at the schematics in the tm but I don't know how to read them. Maybe someone can help me there. Thanks for all your help. You guys are great!


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You are aware there are 2 15amp CB's behind the instrument cluster right? One is the run CB.
if it's all dead, you missing a major ground or positive...I have seen the positive stud on the body pass through ground out before. Check all your battery pos and ground cables, or even replace them if they are old and nasty.

 

[Ang2gna]

Try this method. Turn on your aftermarket lights. Put one probe of your voltmeter on the 24 volt positive battery terminal. Place the other probe on the positive battery terminal of the other battery. Should read 12 volts, if not, the battery interconnect cable is faulty. Next, while leaving the first probe on the 24 volt positive terminal, place the other probe on the shunt. Should read 24 volts. If not, the cable between the negative battery terminal and the shunt is faulty. Lastly, place the second probe on chassis ground. If you don't get 24 volts, the cable between the shunt and chassis is faulty. I think that cable ends on the starter.


See if you can look at the cable strands in the ring terminal without cutting off the shrink sleeve. If you see crusty crap in there, that is the problem.

NDT, you are awesome! Assuming I did the last test correctly I think that is the bad cable. I had to jam the positive test probe between the positive stud and battery clamp, crawl under hmmwv and put the negative on the negative post on the starter. It showed 0.00. So like I said, if that was the correct procedure than I found the wire. All the others tested as you described. It makes sense that that is the bad cable. I've been driving it around in the snow melt so it's been kicking up all that salt and Road grime. Before I buy a new cable I'll clean it up real good and coat the ends liberally in dielectric grease. Thank you again!


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[Ang2gna]

Hot **** NDT! You were right. I pulled the negative cable to the starter and sure enough the brass was green and crusty. I thought I cleaned them up good last year. I noticed when I took off the nut to the battery box it was barely past finger tight. I never think of those connections when I'm checking battery cable tightness. I will now.
Anyway, after cleaning and installing the shiny cable the truck started right up. I thought for sure it was going to be a fried pcb. I hope this helps someone who may have a similar problem. Thanks again!


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