Battery disconnect switch

[Brutusdog]

I want to install a battery disconnect switch in my M1009. If I understand these correctly, I should install it on the ground side of the front battery (still have original 24 volt/ 12 volt system). Does anyone have a suggestion on which style? I want to be able to switch it on and off from in the cab (not have to raise the hood).

The ones I have found online handle varying amp loads. How many amps run through the ground side of a stock M1009?

Thanks!

 

[doghead]

Can I ask, what's your goal? Why do you want to do this?

 

[Brutusdog]

battery switch

My truck drains the batteries when it sits for a couple days. I have been disconnecting the ground when I park it. I don't want to get caught away from home with dead batteries. My son will soon be driving it and I don't see him taking the time to raise the hood and disconnect the battery. Also, the more complicated I can make it to start, the less likely someone is to drive off with it. So, there are a couple reasons.

Is it a bad idea?

Thanks

 

[englishmauser]

No, it is not a bad idea. I have one on my M35A2 for the same reasons.

 

[JAsher45]

i would be curious to see where that parasitic draw was feeding that is draining your batteries

 

[doghead]

I bet you have a bad diode or voltage regulator, on one of your alternators. It would be cheaper to fix that, than add a disconnect.

Unlike the M35A2, the CUCV has both 12 and 24 volt circuits. I am concerned that a disconnect switch on the ground, may cause issues, if someone forgot the switch(off) and tried to start it. If that were to happen, it is possible that "weird" things could happen, and cause damage.

I wouldn't do it.

 

[Barrman]

I second the don't do it line of thought. My reasons are this. The 6.2 is probably the most depended on tight clean starting cirucit connections vehicle I have ever messed with. Adding more connections to come loose, corrode or break will not help you. Then there is the switch itself. Most of the disconnect switches I have ever seen are meant for race car use. They can be left part way on, part way off and are really pretty cheap quality. You have the switch fry the contacts and finding somebody to jump one of your batteries off sure does seem easy compared to rewiring the truck in the middle of the night in the rain with no flash light.

It is your truck, so do what you want. I just think adding more complexity to a must have system instead of fixing the parasitic draw is kind of silly.

 

[lavarok]

If you plan to install a disconnect, keep it under the hood. Use a marine rated switch such as the Blue Sea Systems 9003E. The 9003E is rated for 350 Amps and is designed as a disconnect for use with diesel engines. The #3000 model is rated for 500-600amps if you wanted something heavier.

I can think of several reasons why someone would want this on a cucv. The first time your starter relay or solenoid sticks on you will wish you had one.

All the naysayers here have silly reasons why they think it is a bad idea. "tight" connections? Depends what monkey worked on the truck last. "weird" things?

Regardless if the truck is 12/24 stock; when you switch the chassis and main ground from the battery pack ( front battery NEG ) you have the ability to control 12v and 24v with one simple switch. If the ground is interrupted, there is no power...period.

***Just make sure you run BOTH black wires, the chassis ground (small black wire) and the main NEG (big black wire), to one side of the switch and the other side to the NEG of the front battery. If you don't and you try to start the truck, then you will certainly fry your fuse-able links and that chassis ground (small black) wire.

Be smart, use heavy gauge wire, check and triple check, and you will be fine. I had a starter run on problem I was trying to isolate and installing a cut off switch allowed me to change out components until ultimately finding the cause. Turned out it was a bad starter solenoid.

 

[doghead]

Ian, you are overlooking the fact that, if the front battery ground is not connected, then the rear battery(which normally supplies 24 volts off its' + terminal, will now supply 12v from it's + terminal. It will get a path to ground through the 12V supply wire and "backfeed" through the 12V+ circuits to get a ground. Do that and apply a high amp load and "weird" things will happen.

I am not a "naysayer", I am an experienced CUCV owner and not afraid to give advise without alot of detail.

 

[Brutusdog]

battery switch

Right now I have one of those screw on disconnects attached to the ground. My truck sits for weeks sometimes. When I have left is hooked up the battery(s) drain. When I remember to unhook it, no problem getting it to start after reattaching. My thought was to put a switch, rather than unhooking the screw on deal all the time. Am I missing something? If I unhook the screw on attachment, are you saying I would still get 12 volts of power?

 

[doghead]

You could if you turned something 12v on. Or have a 24v load connected(ie, starter runon)

I am not posting, based on theory here, I have done this, I know first hand.

You need to fix your problem, not add a disconnect switch.

 

[Barrman]

If you look at your truck. You will see the positive post of the back battery goes to the connection on the firewall. The negative for the back battery goes through the 2 gauge wire to the positive terminal on the front battery. Then you have the ground from the front battery. Follow that small 12 gauge wire that leaves the rear negative terminal. Where does it go?

Through that wire, if you tried to start the truck with the front battery completly disconnected. The current would travel through that wire to the fuesable link and blow it. What else down stream of the fuseable link will get blown before the link fuses? That is the question asked in the post above.

Look in appendix F of the -20 manuals and follow all the wires from the batteries. That might help you understand what we are talking about.

 

[Brutusdog]

Battery Switch

OK, so I have been convinced not to add a switch. As I described, I have put in a disconnect, through which the big ground wire and the small ground wire are disconnecting from the negative pole of the front battery.

Until I can figure out what is draining the battery, am I okay doing that? Seems to keep the battery from draining.

 

[Barrman]

Remove any of your battery terminals. Put an amp meter in to complete the circuit with everything turned off. If you are showing anything besides 0, then something is still on. I would start by unplugging the white plug on the side of an alternator. Once the plug is off look at your meter. If it is the same, keep unplugging from that alternator. Then move to the other alternator. Check the meter every time you do something. Keep going all the way back through the fuse panel, ignition and such to the terminal strip on the firewall. Eventually, you will find where the short is. Then, fix it.

 

[lavarok]

I am not a "naysayer", I am an experienced CUCV owner and not afraid to give advise without alot of detail.

I have much respect for you Doghead, but I also "write" from experience. No offense is or was intended to anyone. A naysayer is not a derogatory term.

Ian, you are overlooking the fact that, if the front battery ground is not connected, then the rear battery(which normally supplies 24 volts off its' + terminal, will now supply 12v from it's + terminal. It will get a path to ground through the 12V supply wire and "backfeed" through the 12V+ circuits to get a ground. Do that and apply a high amp load and "weird" things will happen.

Yes - I agree that could happen as evidenced when removing the front bat neg during a "run on" situation. Fusible links on the 12v side will usually burn when this is done.

However, under normal circumstances if the switch is off the 12v relays for the glow plug controller and the starter will never see 12v so they will not close thus not enabling a back feed from the 24v side through the 12v side. In other words, under normal circumstances the switch should work without failure if off and the truck is attempted to be started. Nothing *should* happen. For me and my M1008, it works as described and intended.

If switched from on to off during a "run on", fusible links may fry as a back feed occurs but the same will happen when you finally get a wrench on the terminal to remove the cable from the battery. The switch will allow you to stop the starter much quicker especially if tools are not present. Yes, you may burn some links but that would be unavoidable in this scenario.

I agree a switch does not solve the OPs battery drain problem to root cause. I offered a switch suggestion as that was the question of the original post. Should he fix the truck properly...certainly.

 

[Matt65]

My truck came with a keyed in cab disconnect. I am not sure how it is wired, but will describe how it works. When the disconnect is off everything is totally dead. Once the truck is running and warm I can throw the disconnect and it will keep running. If running and still cold it will kill the engine just as it would turning the ignition key. I have always wondered why it works this way, chime in if you can explain this.

This is a great feature to have that will add to a CUCVs security if not yet re-keyed.

 

[Hoolio]

I put a pair of disconnects on both battery pos terminals under the hood.. I had a start relay stick...What a sickening feeling when you run for a 1/2" wrench to pull battery terminals , just to find out they're 9/16" nuts..I did the relay swap , then made small brackets , attached cut-off switches to the battery hold-downs..Has worked excellent since... Now if only the other gremlins would stop messing with me.....

 

[kentuckycucv]

What if i put the cut off on the positive battery closest to the firewall. Would that cut off everything, or would it bleed through the smaller negative wire that gows toward the gpr???

 

[Mohawk Dave]

Hey guys,

My M1009 has a switch under the hood located between the two batteries. This was straight from the SeaBees. However, when switched off, I have zero power throughout the entirety of the truck. I assumed this was normal trim on these, but I guess not. I will look tomorrow to see how it is wired, but here is the only photo I have of it.

-Dave

 

[kentuckycucv]

Looks like its on the black ground cable?