fuel pump kill using wiper switch

Since I no longer have a rear wiper, I'd like to use the switch as a manual fuel pump kill switch. I happened to believe that things in plain sight tend to hide better than "hidden" switches which are many times quite simple to find.

The switch is very similar to this one:



So I pulled the conrol panel, and the wiper switch has 6 wires grouped as follows:

A) 2 ground
B) 2 +12v (constant)
C) 1 +12v (when in On position)
D) 1 would not measure

Could I simply run the (+) lead going to the fuel pump into both B inputs on the switch, connect both grounds, then run the swiched output C to the fuel pump?

Also, the wires on the wiper harness seem about the same gauge as the fuel pump wires, but I don't know if the switch itself is capable. Do I need a relay? Thanks.

I would not interrupt the fuel pump supply wires. This is just my opinion, but what happens if the switch fails as you are driving?

That being said, you should use a relay to handle the load since you do not know how much power the pump requires. You would use the C connection to turn the relay on, similar to:

Pin 85 Ground
Pin 86 C wire from switch
Pin 87 One side of cut Fuel pump wire
Pin 30 Other side of cut Fuel pump wire.

This will energize the relay when the switch is on, connecting the fuel pump wire and disconnect it when the switch is off.

Good Luck

Do these kinds of switches have a high failure rate? I didn't think there was very much to them. I'm confident enough in my soldering ability and plan to fuse the power lead for added protection, so I'm hoping the chances are pretty slim a problem would occur. If the switch does fail, I could just pull the panel and reconnect the fuel pump normally.

what is the purpose of this mod? I'm not quite seeing what having a fuel pump kill switch does

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Its to stop someone from taking his car. over here fuel pump kill is the norm. companies like cobra give you the fuel pump wire on thier diagrams.

the failure rate of a relay is pretty low. especially a good one.

if it fails while driving its the same a running out of fuel when driving.

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Why oh Why didn't i take the blue pill
Darren Power

Powermyster wrote:

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if it fails while driving its the same a running out of fuel when driving.

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Yes, that is what I was saying. If you do a starter kill, it keeps someone from taking the vehicle as well but the vehicle just will not start, not die while driving. Just my opinion.

The starter kill tends to be too obvious though, so it's not as secure as something like a fuel or ignition cutoff. If it doesn't crank, it's pretty obvious, but if it doesn't start, it's much harder to track down and bypass.
Depends on the level of security needed, and how the driver is going to react in a situation if the car suddenly dies on the road. If it's for a customer who's strictly gas-it-n-go type of motorist, starter kill is definitely better.

If you decide on a fuel cut, use the wiper switch only to control a relay, not to power the pump itself; and set it up so the relay latches on, so the wiper switch isn't needed after you start the car. That way you won't lose power to the pump until you shut the car off, even if you accidentally knock the wiper switch off while driving.
Use a good quality relay and proper connection procedures, and it should be okay.

starter kill dons't stop people push starting a manual trans.. which 99% of cars are on my side of the pond.

that is why i prefere fuel kill

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Why oh Why didn't i take the blue pill
Darren Power

Do a starter kill AND a fuel cut, and you can find the crook passed out down the road from exhaustion-

Yes for the stated reasons I think a starter kill is quite simple to identify and defeat, almost not worth the effort.

I'm thinking about using this switch in conjunction with a shorted cigarette adaptor, so the adaptor must also be inserted in addition to the switch being set in order for the fuel pump to operate. I would probably only yank out the adaptor in higher risk situations, and just use the switch for day to day use.

i wouldn't go with the adapter. you could have a friend or child pull it out on you while driving not knowing what they are doing.. the stalk switch chould be ok presuming its not too easy to knock off by accident.



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Why oh Why didn't i take the blue pill
Darren Power

Wire up the relay in latching configuration and it won't be affected by any accidental unplugging while driving.
The wiper switch/cig plug etc. only has to work once when starting; after the relay is energized, they won't have any other effect.

All you need is a diode to keep the coil energized, and it'll remain on until the car is switched off from the ignition.


Also, make sure your switched trigger signal turns off when you shut down the car, or else the relay will drain your battery down while parked..

Can I also use the fuel pump power line for the wiper switch?

nice one dual.. thats the best way to go alright.

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Why oh Why didn't i take the blue pill
Darren Power

Ahh, I think I follow, it looks like you have the relay continuously re-activating the trigger using the output, that's pretty slick. Thanks for the detailed info!

Important thing is to get a quality relay for this; because you definitely don't want any failures while driving..

This is something I just thought of, which I'm not sure might be better or worse for reliability, but you could put a resistor in line with the D1 feedback diode, to drop the amount of current used in maintaining the relay in the closed position.

That would make it easier on the relay by reducing the power going through the coil for the long periods you're driving; relays generally need less power to hold it closed after the initial closure. You'd have to check the specs on your relay to see how much you could reduce it, based on the hold voltage and coil resistance.

I'd also suggest putting in a backup mechanical switch in a buried/hidden location which you can switch in just in case you do experience a failure- if it happens on the road, it'd be a lot easier flicking a switch than trying an on the road splice/bypass...