If I add a circuit with a relay, and use a fused line coming off the positive battery terminal to pin 85 or 86, is one or two feet a safe distance between the fuse and the battery or should it be closer?

It’s 12g wire and a 15amp fuse. Its the trigger wire for the relay so should only be drawing a few mA.

 

I would say the closer the better and make sure that part of the wire is safe and can't get shorted .

 

Put fuse right near at battery. A fusible link wire is also an option at battery.

 

I added a fuel kill. Relay breaks the line to OEM wiring. Fuse is between battery and relay trigger (85 or 86). 12g wire 15a fuse. Its about 2’ from battery but the fuse should blow before the wire overloads. Relay pulls a few mA, wire is rated for 20a, fuse is 15a.

 

Why are you running a wire to the battery for the kill switch? I thought you were just putting it inline with the fuel pump wire, and using that wire to power the relay? If you're grabbing power for the relay from the battery, that's an extra drain on the battery if you don't flip the relay off every time. Depending on the relay, around 50-150 mA.

 

It was easier to grab power from the battery than from the line I used based on where I interrupted it. The switch will always be flipped when parking for longer than a short period of time, and probably more often than that.

 

Hmm, okay. Would have been just connecting the incoming fuel pump power to two pins instead of one?

Had an interesting idea for a non-obvious kill switch - the ash tray. If open, no fuel pump, and it has to be flipped up to enable the fuel pump. No thief is going to think about closing it when rummaging around right?

 

Can you recommend a good multimeter for testing current? I have seen a few but one of them says not to test over 200microamps so maybe I'm looking in the wrong place.

 

@lawsoncl thanks for pointing out the constantly-on relay that I didn’t think of. With the relay going and the car off, theres about a 160mA load on the battery. I’ll have to remember to flip the switch every night, which I should be doing anyway.

I was curious how much the under hood light would draw so I left if connected, disconnected the negative terminal, and hooked up the multimeter but I couldn’t get the bulb to light. Why would this be? Maybe I had the multimeter set to too low of a value?

 

Actually the cheap Harbor Freight house brand ones aren't too bad. Some will do 20-amp, which I consider the minimum for auto work. I still have a handful of the HF cheapies in the box that only do 5-amp current that I picked up for $1.49 each. I actually bought a whole case and have been giving them away whenever someone wants to borrow a meter. I also tossed one in each car, and have given those away on occasion as well.

 

@lawsoncl why wouldn't the underhood bulb light up with the multimeter wired in series with the negative battery terminal?

 

It should unless the bulb or switch in it are bad.

 

@lawsoncl the underhood bulb works. If I wanted to see how much current it was pulling (in a situation where it never shut off), I would disconnect the negative battery terminal, put the multimeter in series, and the bulb should illuminate with the current running through the multimeter, right? What would be the appropriate setting to have the multimeter set to? I’m wondering if I had the meter set to mA and the bulb pulls too much for that setting.

 

@lawsoncl could I use the + terminal on the starter relay so that there isn’t a constant draw? I don’t know if that terminal has constant power when the car is on or only if while starting but based on the amount of wires I see attached to it I would assume it could be a good spot.

 

Use you meter and see what terminal is live only with the key-on. I would have just connected it to the existing wire at the relay. You could also connect to something under the dash that has power when the key is on. Tap into one of the fuses, for example.