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Hey all,

I am having trouble with a friend's M38 CDN and we are trying to diagnose the problem. It is driven regularly, as recently as last Thursday. It always starts and runs well.

I went to start it on Monday and it didn't want to start. Cranked but didn't want to catch. Batteries were low, so I plugged her in for a 20 minutes. Fired up after that no problem with her own batteries.

Drove for 20 minutes, pulled in to the driveway and turned her off. Came out 15 minutes later, attempted to start her up but power was so low that it almost wouldn't turn over.

Tried push starting which she usually catches no problem, especially when warm. No dice. Got half way around the block, still nothing, went back for the truck. Towed started after 5 or 6 attempts.

Drove 20 minutes, stalled out going in to gas station. Push started first time.

Over the next hour of driving the problem has evolved to the point where she will run and drive fine on her own, but if you try and turn on the lights, she will die out.

I am assuming that it is a problem somewhere in the electrical, possibly charging. Visual checks on all connections appear fine... Any suggestions on where to start?!

What does the amp or volt gauge say it's doing? Have you taken a reading with a multimeter across the batteries at high idle to see if you are charging?

Sounds like you have a drain on the system when off. Check with a test light between the ground and battery post disconnected with the key off. If it lights the light, you have a short. M38's had a starter 24 contact where the leads attach that was notorious for a internal short. Hard to find if you don't know about it. John

Hawkshadow wrote:Hey all,

I am having trouble with a friend's M38 CDN and we are trying to diagnose the problem. It is driven regularly, as recently as last Thursday. It always starts and runs well.

I went to start it on Monday and it didn't want to start. Cranked but didn't want to catch. Batteries were low, so I plugged her in for a 20 minutes. Fired up after that no problem with her own batteries.

Drove for 20 minutes, pulled in to the driveway and turned her off. Came out 15 minutes later, attempted to start her up but power was so low that it almost wouldn't turn over.

Tried push starting which she usually catches no problem, especially when warm. No dice. Got half way around the block, still nothing, went back for the truck. Towed started after 5 or 6 attempts.

Drove 20 minutes, stalled out going in to gas station. Push started first time.

Over the next hour of driving the problem has evolved to the point where she will run and drive fine on her own, but if you try and turn on the lights, she will die out.

I am assuming that it is a problem somewhere in the electrical, possibly charging. Visual checks on all connections appear fine... Any suggestions on where to start?!

It sounds pretty obvious that your battery is dead AND is not being charged. It also sounds like the charging system isn't working since it won't keep the Jeep running with the headlights on ( a significant short in the headlight system might produce the same results). Battery maybe ok if you charge it externally but if you leave it sitting dead for very long (overnight if it's old) it WILL ruin it. Charge the battery w/ an external charger and then start the Jeep* and see what the volt or ampmeter says. I'd also use an external voltmeter to monitor the charge voltage at the battery, The TMs lists the normal battery voltages for different conditions (engine on or off, headlights on or off, etc. And if you can get an amp meter rated at at least 25 amps then hook it up too and see what's going on. An ampmeter is the best way to see what the charging system is doing. Too many other things can affect a voltmeter.

*If Jeep won't start due to weak or dead battery even after charging it with an external charger then you're going to have to replace the battery(s). You can also take the battery(s) out and take them to a local auto parts place and most of them will charge and check your battery(s) for free.

AFTER you have known good battery(s) then you can troubleshoot the Jeeps charging system.

Thanks for the replies gents. I have the batteries on charge now and will let you know what I find.

If the jeep's generator and regulator are stock it has an amp meter in the dash. That is your only indicator of the jeep's electrical generating system output. Was it reading a charge, discharge, or "0" when the jeep is running?

When you finish charging the batteries leave the ground cable on the front battery off. Connect a 24 volt test lamp bewteen the end of the cable and the battery's negative terminal. Withe the ignition and light switch off the light should NOT light up. If it does light up you have a current drain in the system that needs to be repaired first. That is a complete detailed troubleshooting event that can be addressed when you let us know the answers to our questions.

Those questions again are:

1-Is the jeep's electrical system the original stock 24 volt 25 amp system?

2-What does the amp meter while the jeep is running?

3-Did the test lamp light up?

We can offer much more precise help if you will first anser these questions/

I was having similar problems recently. Purchased a hydrometer and tested my batteries and found two dead cells in one and one dead cell in the other. The symptoms were slightly low voltage across both batteries. It would run off the generator but the ammeter was only showing slightly on the plus side of dead center. When I tried to start it off the batteries the gauges would go dead, if I had the lights on they would instantly go out, If I used jumper cables across the battery with two dead cells it would start normally. I replaced the batteries and all is back to normal.