Kill switches and electricity

Hey guys, lots of XJ thefts around here lately so I am attempting to install a kill switch.

First hurdle is understanding relays. Can the switch circuit and the accessory circuit, within the relay, be powered by the same source? Or do I need a low-voltage/low-amperage source for the switch circuit (so as not to burn out my switch), and another high-voltage/high-amperage source for the accessory?

The idea behind a relay is to keep you from running high amperage through a switch. This means you can use lower gauge wires, the switch can be located further away from the power source, etc etc.

With all that in mind, your battery/alternator provides a 12V power source - that's where you're gonna power your relay from and where you're gonna power whatever device the relay is interrupting. If you've got a fancy lit switch, that 12 volts are gonna power that too.

Thanks @essvee.

So as I understand it, because everything is powered by the same battery/alternator, I can use the same power line to power both circuits in a relay (accessory & switch circuits).

My next question is how do I figure out the amperage rating required for the switch? I have some switches here that are rated to .5 amps. This number seems too low, but is it?

BALTANAKT said:

Thanks @essvee.

So as I understand it, because everything is powered by the same battery/alternator, I can use the same power line to power both circuits in a relay (accessory & switch circuits).

My next question is how do I figure out the amperage rating required for the switch? I have some switches here that are rated to .5 amps. This number seems too low, but is it?

Click to expand...

Yes, in fact that's probably the simplest way to do it. Then you only need to run a single wire to the switch, the switch will then connect it to ground. The coil in the relay isn't going to pull more a 0.02 amps so 0.5 amps in more than plenty.

Thanks Lawson!

Next Q: Is 16ga wire acceptable for the current running the fuel pump?

Main reason I ask is because I've read some threads that say Jeep actually used 16ga *and* 14ga for the pump circuit. And 16ga being what I have on hand, it would be convenient.

2000 FSM shows the wire to the fuel pump from the relay is 16-guage. You could put your switch inline with the wire that controls the existing fuel pump relay.

If you're planning on putting a kill switch in the coil circuit of the fuel relay (or ASD relay, etc.), bear in mind that a paperclip inserted into the relay 30 and 87 cavities will defeat your switch.
My thinking is that in order to start your XJ, the thief will HAVE TO get into the passenger compartment to access ignition, steering lock, shift lock, etc., at which point popping the hood and using the paperclip will be easy.
And if the thief is incapable of doing all of the above, then whether or not your kill switch is off or on will be irrelevant.
If you installed your kill switch into the actual fuel pump 12V supply line, that would work better...but it involves under the hood or under the XJ wiring, and I made the choice to not get into it that far.

The two things I did to my '99 XJ are:
1.) Padlocked the transfer case shifter fully forward (to a heavy metal strap bolted under the dash), so that the XJ cannot EASILY be towed away on one axle (or rolled off a cliff by vandals, etc.), and
2.) Installed a switched jumper between the horn wire and the door switches, such that opening any door causes the horn to honk (the rear lift door already has a "disable" switch from the factory that allows me to arm/disarm the alarm through the rear entry). Not as good as a sophisticated alarm system, but somewhat better than nothing.

Thanks fellas.

Q: Is it ok to use the chassis for the ground coming off my relay?

Yes as long as you remove any paint or coating so that you get a good ground.

I simply used the ground wire for the pump and switched that.

However, it's all really moot. There are plenty of crooked tow truck drivers out there. If they want it, they will get it.

Since I keep my XJ in a locked garage in my back yard, I'm not too worried about theft. The kill switch was more to add some protection from joy riders and other adolescents for when the XJ is not locked in the garage.