Installing a fuel pump cutoff switch

[mooty]

I was looking to add a little security to my ranger by installing a fuel pump cut-off switch. I have very easy access to inertia switch leads and I am told green/yellow comes from the computer controlled FP relay. I'm just curious if this is a safe place to install a toggle switch?

 

[Die.Fledermaus]

I think it is a good idea, better than the "starter interrupt" that many car alarms implement.

 

[RonD]

I was looking to add a little security to my ranger by installing a fuel pump cut-off switch. I have very easy access to inertia switch leads and I am told green/yellow comes from the computer controlled FP relay. I'm just curious if this is a safe place to install a toggle switch?

NO, it isn't.
You do not want to run 30amp wires to a toggle switch, you are just asking for trouble.

But since you already have the FP relay why not use it.

The FP replay is controlled by the computer using a Ground.
When key is turned on the FP relay gets 12volts but has no Ground so doesn't close to send power to fuel pump.
Computer controls it's Ground.

If you were to intercept this Ground wire on the FP relay and run 2 GROUND wires into the cab, you would be safe from shorts and computer Ground control would only work when toggle switch was closed, so when switch is "off" FP relay never closes and fuel pump never gets power.

You can of course do the samething inside the cab at the inertia switch with another 30amp 12volt relay, same as FP relay.
The Pink/black stripe wire would be the one to use, that is the 12v OUT to fuel pump.
And same as computer control, you would use the toggle switch to control the GROUND that closes this relay, so no shorts.


In either setup you will probably get a CEL(check engine light) because computer monitors fuel pump power, when computer Grounds FP relay it expects to see 12volts on the fuel pumps power wire, when it doesn't see that it will notify driver of the problem.
CEL will go off when power is restored, toggle "on".
The "probably" above is important because it depends on where the computers wire to monitor voltage is spliced into the system.

 

[mooty]

NO, it isn't.
You do not want to run 30amp wires to a toggle switch, you are just asking for trouble.

But since you already have the FP relay why not use it.

The FP replay is controlled by the computer using a Ground.
When key is turned on the FP relay gets 12volts but has no Ground so doesn't close to send power to fuel pump.
Computer controls it's Ground.

If you were to intercept this Ground wire on the FP relay and run 2 GROUND wires into the cab, you would be safe from shorts and computer Ground control would only work when toggle switch was closed, so when switch is "off" FP relay never closes and fuel pump never gets power.

You can of course do the samething inside the cab at the inertia switch with another 30amp 12volt relay, same as FP relay.
The Pink/black stripe wire would be the one to use, that is the 12v OUT to fuel pump.
And same as computer control, you would use the toggle switch to control the GROUND that closes this relay, so no shorts.


In either setup you will probably get a CEL(check engine light) because computer monitors fuel pump power, when computer Grounds FP relay it expects to see 12volts on the fuel pumps power wire, when it doesn't see that it will notify driver of the problem.
CEL will go off when power is restored, toggle "on".
The "probably" above is important because it depends on where the computers wire to monitor voltage is spliced into the system.

I took your advice and found the fuel pump relay ground lead coming out of the power distribution box and to the PCM. Conveniently, this is one of the outer most wires in the section where the wire bundle feeds the box. The FP relay sits right above the bundle and the wire is blue with orange striping.

I fed my new leads over the brake drum and through what I believe to be a steering column grommet/boot. I've read a lot of people use this section to feed wires through the fire wall. I added some heat shielding on the part of the wire closest to the engine. From there I setup an ashtray switch and am good to go.

I do kinda wish I had a less obvious spot but this will do for now.



I tested it and it wouldn't turn over while the check engine light came on, just as you stated.