Battery disconnect switch that fits? M998

Is there a battery disconnect switch that will fit on the battery and under the passenger seat tray for a M998 A1?

Would you put it on the negative or positive lead?

I prefer breaking the negative side, this is a must if you have dual voltage alternators. Cat however breaks the jumper between the batterys.

I installed one with a key in front of the shifter area that I got off of the large online auction site. I painted it green. I set mine up to break the ground side using 2/0 wire and used my hydraulic crimping tool. I think it took roughly 2 5' sections of wire which I also wrapped in that Chinese finger cuff sheathing for abrasion resistance and I put marine grade heat shrink over the ends to cover the cut ends of sheathing and look professional. I do plan to submerge this Vehcile so I am taking every precaution I can.

AOR said:

I installed one with a key in front of the shifter area that I got off of the large online auction site. I painted it green. I set mine up to break the ground side using 2/0 wire and used my hydraulic crimping tool. I think it took roughly 2 5' sections of wire which I also wrapped in that Chinese finger cuff sheathing for abrasion resistance and I put marine grade heat shrink over the ends to cover the cut ends of sheathing and look professional. I do plan to submerge this Vehcile so I am taking every precaution I can.

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that is clean looking. Actually an additional anti-theft device I would imagine.

others put their switches in this area before me but yes living half way between DC and Baltimore anti theft was the main reason for this setup it also saves time when servicing the vehicle. I also have a threaded cap I can put on this to further conceal it. If someone knows what they are doing they can easily steal the vehicle but that is what insurance is for

I've got a switch coming now. I'm going to put it in the spare open compartment next to the batteries under the passenger seat. I think I can use the original ground cable to battery to go to the switch and just make up a new one to go to the shunt lug.

Need to search around now for a reasonable priced 24 volt battery tender.

I've managed to accumulate way too many things with batteries over this last year that all need to be maintained over the winter.

Here is what I came up with. But in retrospect I should have gotten the other type of switch and put it where the original auxiliary port was under the front corner of the passenger seat - then I could access it without lifting the seat cover. What I did do is have enough cable due to that port and my current battery ground to put the switch over out of the way in the chamber next to the main battery box. It is a marine quality switch so getting it wet shouldn't be a big deal.

Here’s what i did. Works great. Keyed (sort of).

https://www.steelsoldiers.com/showthread.php?170794-M998-Battery-Shutoff-kill-switch-My-final-setup-with-pictures&highlight=

Look into battery shut off switches from the drag racing world. Completely overbuilt, strong, will never break, and can be mounted anywhere.

So...here is an update. I noticed that when I disconnected using the switch, the system still had voltage! Brake lights would still illuminate as would my 24 volt dome light mod. I hooked up to the rear most battery positive terminal for the 14 volt system. As long as they stays connected, it is backfeeding 14 volts through the system. I hope this hasn't damaged the glow plug box/controller...but as far as I know I haven't turned the key to run any time I've had the battery in disconnect.

So, I suppose I can either add another disconnect for the 14 volt, or rewire so the main disconnect breaks between the batteries - but I don't know if then putting it on the front battery negative post side would have any impact on how I want it to charge.

That's right. BAD NEWS BEAR, If you placed your disconnect switch to disconnect the rear battery ground and using the 12/14 volt tap at the center of the two batteries to feed 12/14 volt circuits. Now the 12/14 volt equipment becomes the ground return of the front battery. Trying to pull a load from the front battery as in trying to start or / and anything that works on the 24 volt system, it NOW has a path to ground thru... you guessed it, the equipment.

BAD THINGS are going to happen.

Ouch, equipment fuses and maybe smoke,

CAMO

I had a similar issue I have the 100 amp alternator. I made what I thought was a good setup and connected a power inverter to run my job site radio and have USB ports. If the power inverter was plugged in even with the its switch in the off position I would get some voltage when turning the switch to the run position when the disconnect was in disconnect mode. I spoke to the alternator mfr and they said it was back feeding through the 12 volt portion of the alternators voltage regulator. I hope this helps. For now I have the 12volt system unhooked and only run the radio on its own battery power and if I need to charge them I can plug in the inverter. Its been over six months with my usage I have not needed to charge the Milwaukee battery packs or my phone yet. I may have cooked a glow plug controller box because of this.

As far as I know I haven’t hurt anything yet. As I haven’t attempted a start or key on by accident after installing the cut off switch. I have another switch coming so I can kill both when not in use.

Right now the rig is down waiting on a power steering gear. Hopefully I’ll have that by this weekend and we will see.

But it was electrically working fine prior to me taking the steering gear out.

I quickly drew this up for you, it should work to keep the 12v circuit from backfeeding. Ignore part numbers, I just grabbed random parts for the schematic. Basically use a heavy duty relay/solenoid switched with a 12v master ON switch. If the disconnect on the ground is flipped off without turning off the 12v master the diode prevents the current from reversing through the relay and the relay drops out. Ignore the lamps and fan, they were only added for visualization.



Mike

Would this circuit draw amps when the main disconnect is connected to keep the relay closed?

Current only flows in the 12v circuit when the 12v master is on. The current required to energize the relay is minimal, a couple hundred milliamps, but I would still switch it off when you park it. The easiest way is if you have a switch panel for your accessories just make the first switch the 12v master. You can also swap out that switch for a 24v relay powered off the run switch so the circuit automatically shuts off with the engine.


Mike

First, thanks to Milcommoguy for the heads-up on this. I just got my first A2 vehicle, and was just about to throw in a simple disconnect-ground-switch. That´s definitely not enough. I was glad I found this here just in time.

However, I´ve been thinking long and hard about this, and I wondered why the TMs don´t mention the problem of the 12V take-off. Cutting off ground with a switch is the same as taking off the ground cable from the second battery during maintenance.

I was also worried that two relays, even when activated at the same time, might create a voltage spike in the electronics due to slightly different mechanical timings for opening.

So I took an amperemeter, and checked for the actual current in the 12 V output while everything is off. The lead is numbered "290/291/537" by the way, and in a stock M1045A2 (I don´t have any other 12 V gadgets in yet), it´s just running to the TCM, and to the tranny relay (which is off when "Run" is off). There IS in fact a small current flowing to the TCM, even in a completely switched-off Humvee, of about 3.0 milliamps.

This means that by ohm´s law (at least at rest), a TCM has a resistance of about 4 Kohms, which is quite a lot.

I´m convinced now that, yes, a second relay in the 12 V take-off makes sense (at the very least to stop that 3 milliamps from slowly draining your battery). But I think that due to the quite high resistance of the TCM there is no immediate danger when you take off just the ground cable on the second battery.
But I´m just a mechanical guy trying to understand electrics, so feel free to correct me.

For now I just added a second disconnect. One for the main ground and one for the 12+ connection

Now I know it is 100% dead when I rotate both switches.