Sparks fly when connecting batteries

[rodent]

I recently purchased my first military vehicle. 1986 M1008

Trying to troubleshoot a battery drain on both batteries that happens over night. I think I finally traced it down to either a trailer brake controller previous owner added or the front and rear lights on the bumpers. EVERTHING is disconnected including the brake controller, lights, all fuses, and BOTH alternators. When I connect the last connector on the front battery, I get big sparks. Is this normal on the 24 volt system? Both batteries are charged and have equal voltage. I made sure any disconnected wires are not touching anything.

Took a picture of the batteries and cables. Is this correct or is there anything that looks wrong?

 

[Scar59]

Battery looks to be wired in series, which is correct. (if your blue post it notes are correct). Disconnect the true negative lead, connect the positive leads and make the negative lead the last connection, this should minimize the sparking. A large spark normally means the system has a significant draw on it.

 

[rodent]

Battery looks to be wired in series, which is correct. (if your blue post it notes are correct). Disconnect the true negative lead, connect the positive leads and make the negative lead the last connection, this should minimize the sparking. A large spark normally means the system has a significant draw on it.

Thanks! I'll try that. I thought maybe my alternators were causing the draw with a bad diode but with both disconnected of all wires I now think it was the brake controller or the bumper lights. Didn't have time to pin point which one on my lunch hour.

Is there any other common battery draw issues these trucks have?

 

[porkysplace]

Thanks! I'll try that. I thought maybe my alternators were causing the draw with a bad diode but with both disconnected of all wires I now think it was the brake controller or the bumper lights. Didn't have time to pin point which one on my lunch hour.

Is there any other common battery draw issues these trucks have?

You will find a ton of information on electrical issues in this link;
[h=1]CUCV Helpful Threads[/h]

 

[Timeline98]

Do you have a test light or DMM with an AMP (Current setting)?

To trouble shoot for a draw, place the test light or DMM (set to measure current. Usually limited to 10amps) between the Battery Negative post and the Negative wire (this is the wire/connection that normally goes on the battery).
1. If the test light lights up, or amperage is present on the DMM, there is a draw on the battery.
2. At this point, you can disconnect ONE fuse at a time until the Light dims or Amp reading is reduced. (IF no change is noted, plug fuse back in and continue on to the next fuse) **Also remember the fuse location for each fuse. Might want to take a picture for quick reference**
3. Do this until the light goes out or little to no amps are displayed on the DMM.
4. Find what component is wired to the circuit that created a draw on the battery. At this point you should have found the faulty or high draw component.
5. To resolve the draw issue, you may want to consider hooking this up to an ignition ON source or replace if it is believed to be defective.

***Do NOT turn the key ON or try starting the vehicle with the test light or meter installed between the battery and Neg. cable***

 

[rodent]

You will find a ton of information on electrical issues in this link;
CUCV Helpful Threads

Thanks I will look there.

Do you have a test light or DMM with an AMP (Current setting)?
To trouble shoot for a draw, place the test light or DMM (set to measure current. Usually limited to 10amps) between the Battery Negative post and the Negative wire (this is the wire/connection that normally goes on the battery).
1. If the test light lights up, or amperage is present on the DMM, there is a draw on the battery.
2. At this point, you can disconnect ONE fuse at a time until the Light dims or Amp reading is reduced. (IF no change is noted, plug fuse back in and continue on to the next fuse) **Also remember the fuse location for each fuse. Might want to take a picture for quick reference**
3. Do this until the light goes out or little to no amps are displayed on the DMM.
4. Find what component is wired to the circuit that created a draw on the battery. At this point you should have found the faulty or high draw component.
5. To resolve the draw issue, you may want to consider hooking this up to an ignition ON source or replace if it is believed to be defective.

***Do NOT turn the key ON or try starting the vehicle with the test light or meter installed between the battery and Neg. cable***

View attachment 714342

Thanks for the info. Already pulled ALL the fuses so they are not installed at this time. I do have an amp meter for 10amps or less. I do have more than 10 amps going through the last battery wire I connect. I haven't tried the ignition switch yet.

 

[n8roro]

It sounds like a short to me. You could disconnect the wires to the slave port and going from the 24v terminal to see if the issue goes away. You can do it one by one and test in between to isolate where the short is. I'm a CUCV novice though.

 

[rodent]

It sounds like a short to me. You could disconnect the wires to the slave port and going from the 24v terminal to see if the issue goes away. You can do it one by one and test in between to isolate where the short is. I'm a CUCV novice though.

I'll give that a shot. I've connected a many batteries over the years dealing with cars and never had one arc like this. Very frustrating when you all you want to do is drive it. Also my third gear is slipping so I have that going for me too.

 

[Scar59]

Thanks for the info. Already pulled ALL the fuses so they are not installed at this time. I do have an amp meter for 10amps or less. I do have more than 10 amps going through the last battery wire I connect. I haven't tried the ignition switch yet.[/QUOTE]

Oh yeah, 10 amps will make a big spark, sound like you're headed in the right direction. You may have a wire chaffed through to the frame/body. Keep a fire extinguisher close.

 

[tobyS]

Seems like you should use the Ohmmeter, something that large I would expect to read a dead short. keep the battery disconnected

 

[MarcusOReallyus]

I would NOT try to measure current with a meter until you have stopped making sparks. You stand a really good chance of frying your meter.

A test light or voltmeter will tell you what you need to know. Current measurements aren't useful at this point. The draindown is the least of your worries at the moment.

When I connect the last connector on the front battery, I get big sparks.

What's the "last connector"? Looks like you have the ground connected, and the hot lead disconnected on the front battery. You should always disconnect the ground first, and reconnect it last.

Is this normal on the 24 volt system?

Nope. Not even a little bit.

I suggest you start from scratch. Using the info in the Helpful Threads sticky, work out the correct wiring. Start with the batteries (ground disconnected for now) and start tracing wiring to see what belongs where. Correct any problems you find.

Also check your fusible links - you might have fried one.

Once you think you have it all connected correctly, place a test light or voltmeter between the front battery ground and a good ground point on the chassis. If everything is correct, and there are no shorts, it should not light.

By the way, be especially careful about the alternator wiring. That's an easy place to go wrong.

 

[Tow4]

Disconnect the glow plugs at the solenoid. I can't think of any other high current draws unless something is going on with the glow plug resistor on the firewall.

 

[rodent]

Oh yeah, 10 amps will make a big spark, sound like you're headed in the right direction. You may have a wire chaffed through to the frame/body. Keep a fire extinguisher close.

I hope its something simple. Whats funny is I bought the truck like this with the batteries connected. Charged them up, re-connected and drives around fine. But you are right, need to keep an extinguisher.

Seems like you should use the Ohmmeter, something that large I would expect to read a dead short. keep the battery disconnected

I agree.

I would NOT try to measure current with a meter until you have stopped making sparks. You stand a really good chance of frying your meter.
A test light or voltmeter will tell you what you need to know. Current measurements aren't useful at this point. The draindown is the least of your worries at the moment.

What's the "last connector"? Looks like you have the ground connected, and the hot lead disconnected on the front battery. You should always disconnect the ground first, and reconnect it last.
I suggest you start from scratch. Using the info in the Helpful Threads sticky, work out the correct wiring. Start with the batteries (ground disconnected for now) and start tracing wiring to see what belongs where. Correct any problems you find.
Also check your fusible links - you might have fried one.
Once you think you have it all connected correctly, place a test light or voltmeter between the front battery ground and a good ground point on the chassis. If everything is correct, and there are no shorts, it should not light.
By the way, be especially careful about the alternator wiring. That's an easy place to go wrong.

I'm actually shocked my cheap Harbor Freight MM is still working. I went to measure voltage with one of the leads plugged into the amp port. Started to smoke for that one second. Still alive.
I do have the ground connected and I realize you should connect that last and not the positive.

I'll check the fusable links along with glow plugs.

I made sure to label the alternator wires. I just hope it was done right with the last shop that worked on it .

Thanks so much!

Disconnect the glow plugs at the solenoid. I can't think of any other high current draws unless something is going on with the glow plug resistor on the firewall.

Will do that next.

So to re-cap-
-Purchased 2 new batteries
-Removed alternator wires from both
-removed all the fuses inside above brake pedal
-disconnected the bumper light switches front and rear
-disconnected trailer brake controller

Still getting sparks connecting last battery terminal. I am also getting a bright light with a light probe between the battery terminal and cable and more than 10 amps. Definitely a good amount of current.

Checking fusable links and glow plugs next.

 

[cucvrus]

What about the main battery cable on the starter. I have seen these cables butchered / rubbed thru, mis-routed , burnt thru, pinched and new bigger eyes/lugs crimped on with hammers and grounding out. Just a thought. Easy enough to check. Looks a little busy and modified under the hood. Good Luck.

 

[rodent]

What about the main battery cable on the starter. I have seen these cables butchered / rubbed thru, mis-routed , burnt thru, pinched and new bigger eyes/lugs crimped on with hammers and grounding out. Just a thought. Easy enough to check. Looks a little busy and modified under the hood. Good Luck.

Will look at that too. Since I can actually connect the battery and start the truck, I think its a load like the glow plugs or something. I don't think its a short then there would be smoke and melted wires somewhere. I just need to keep disconnecting stuff until I find the culprit.

Thanks again to everyone's help on this matter!

 

[Migginsbros]

Disconect the main lead to the starter to check if the pinion gear stuck in the gear ring and the close circuit of the solenoid cause the issue.
There is no fuse between the starter main + cable/solenoid/batterie.

 

[dependable]

Check that the starter lead is not shorting out on starter heat shield and is connected correctly, had that happen once. Is starter solenoid is stuck on in run out position? Is glow plug relay stuck on? Two other things to check that would draw a lot of amps.

 

[Barrman]

2 possible places for power to normally go from the batteries.

24 volts to the bus bar on the passenger side firewall. From the rear battery positive terminal.
12 volts to the diamond shaped bus bar next to the master cylinder on the small red wire from the back battery negative terminal.

It is a lot easier to unbolt the 24 volt lead at the big bus bar by standing next to the front tire with a socket. Unbolt the lead and see if you still get sparks. Yes, and you are on the 12 volt side for trouble shooting. No and then you probably will end up pulling the starter motor after you check the slave cables going through the valence and the glow plug system if that is still 24 volt.

 

[rodent]

FINALLY found the issue!
Glow plug solenoid. Soon as I removed the wire going to the bus bar, my 12v probe showed no current. No sparks either.
So now I need replace this. Hopefully its wired correctly. Previous owner did replace glow plugs but doesnt look like this was messed with.
Appreciate all the help!

 

[MarcusOReallyus]

It appears to be correct. Expect your GPs to be fried now.