After reading about the unfortunate among us who have suffered a fire in their rig, and how a battery cutoff can help, I plan to purchase both a fire extinguisher and battery cutoff, the latter of which will be handy (on the negative side) for more than fire control.

My question is this: would it make sense to install one on the positive terminal to deny voltage to whatever component or wire is "sparking"? On the neg side would kill the truck, and all electrical if working properly, but am I right to think that if a wire is shorting to ground, say, in a non-grommeted firewall hole, only pulling the positive would deny it voltage?

If that's the case, one on each battery terminal would be ideal? I do realize that any work done requires the neg cable be disconnected first! That wasn't a fun thread....lol

 

If you kill the ground you kill the entire truck. No need to cut off the positive side.

 

Cool. I'm not an electrician, obviously, but I do play a mean electric guitar! So if the negative cable is off the battery, I could short the positive terminal to a bare metal part on the truck and nothing happens? Only if the bare metal is connected to the battery is a circuit completed? I swear I'm not trying to be difficult - I believe you, I'm just trying to learn and understand!

Thanks!

 

Correct, for the same reason you always disconnect the negative cable first and reconnect it last. This way, if you short your wrench against metal while loosening the positive terminal, nothing happens.

As CO explains, you only need the one cutoff (negative terminal). If the positive is connected, but there's some loose wire somewhere that's shorted to sheetmetal, it won't matter because that sheetmetal has no connection to the negative terminal of the battery if the negative-side kill switch is open. Both terminals of the battery have to be connected for any current to flow.

There are no such things as stupid questions when asked by honest people. And there's no such thing as being too careful when it comes to lead-acid batteries. If everybody took the time to learn like you are, there'd be a lot less trucks in the junk yards with giant orange stains underneath the hood from a battery explosion.

 

Fantastic!

Safety first, always. While my dash, instruments, and all the formerly mouse-infested ductwork is out I'm toying with the thought of a new wiring harness, but I don't see any chewed wires, and that's a lot of money, time, and effort, so I'm hedging my bets and will install firewall grommets where there are none, closely inspect the existing wires, get the extinguisher and battery cutoff switch first. If it looks ok, I'm gonna roll with it for a while.

So much to do to this needy vehicle.

I finally ponied up for a 3 year membership - the info here is worth the price of admission! Plus there's a tshirt! Like I've said before, I'm a guitar player and lucked into finding the TDPRI forum. That, and this forum, are both great - lots if very nice folks willing to help, and very little rudeness or meanness.

Thanks!