Crazychopstick

I've read several threads concerning fuel shutoff switches as theft deterrants and I have a question about the wiring:

Most people who do them wire the switch into the 12v lead, but would it not be simpler, if possible, to wire a switch to the fuel pump ground instead?

Would this have any adverse effects(disrupting other electronics sharing ground, blowing fuses, etc)?

midiwall

Either way will be fine... if the ground is easier to get a hold of, then go for it. You're trying to shutdown current flow through the pump, and in this circuit you can do it from either side.

In fact, you could even argue that it would be "better" to switch the ground... If someone suspected that you installed a cutoff, they may first think "oh, he clipped the positive side, so I'll just hot wire to the pump there". But low & behold, you had clipped the ground.

paddlenbike

iTrader: (1)

Be careful switching either the positive or the ground, the fuel pump wires carry a decent load. Either put a relay across it or better yet, put a switch across the ground of the factory relay. Anyone know where it is?

Crazychopstick

I would think it would be better and easier to use the ground.

I know the positive side would benefit form an inline relay to cut down voltage drop but would a relay on the ground side be neccessary?

04 Rocko Taco

I have thought a few times about putting a cut off on my fuel pump also, and always planned on using the ground...so what do we think YT'ers? Relay on the ground side a must?

midiwall

The use of a relay is not about minimizing the voltage drop, it's about having a switch in the circuit that can handle the load of a fuel pump.

Figure on the fuel pump drawing about 12-15amps, and remember that it's a continuous load. The common automotive relay is rated at 20amps, with the "heavy duty" ones being 30amps. There are a gajillion switches that you could buy, and you'd have to pay attention to the current rating.

So, if you pay attention to the switch that you're buying, you'll be fine. But, a decent 20amp switch will probably cost you more than a small 2amp switch and a 20amp relay. Plus, the smaller 2amp switch can be more easily hidden, then you can "remote" the relay closer to the fuel pump.


A "must"? No, but see above.

HaveBlue

I have a stash of Wal-Mart switches at home that are supposedly rated for 30 amps. They only cost me about $3 each. On the other hand, a relay from NAPA, Checker, etc costs $9+. I'm not an electrical guru, so am I missing something?

On a side note, I had one of those 30-amp switches switching the ground on my electric fan. The swtich itself would get VERY hot. At one point, I could smell that acrid electric smoke smell. I figured it was due to the current passing through that switch. I have since changed the switch over to the "switched lead" on the fan's relay. Given that, I would assume that if you are switching the ground, a relay would be a must. Otherwise, the fuel pump already has a relay with a switch. Why not put a switch inline on that?

Does anything I just typed make sense?

midiwall

Hmm... see below.


Correct, and umm, that switch wasn't rated for 30 amps.


Umm, no... the "switched" lead on the fan relay is the power to the relay's coil.
The load current (the fan, or fuel pump) flows from C -> A or C -> B depending on how you wire things up. The connections for V1 & V2 are where you apply current to energize the relay, this current will be very low. When you moved the switch to the fan's switched lead, you're now switching the current driving the coil on/off.


One thing to keep in mind about the "positive" or "ground" question is that current flows from negative to positive, it will flow through BOTH of those leads. And the current will be the same if measured on the ground wire or the positive wire.


And... you could certainly do that! The only downside is getting to the relay to switch the coil. I'm not sure where it is (on my truck), but I'm thinking it's buried somewhere.


Always!

HaveBlue

Isn't it just above the fuse box on the driver's side inside the cabin? From memory, I *think* one might be able to remove that panel to gain access to the wiring behind the relay. Given it's location, too, that might also be a good place for the switch to be hidden. Especially up behind the panel.

I wondered about that.

BruceTS

actually you could always add a switch in the fuse box cutting power to the EFI relay.....

CJM

Or just remove the EFI fuse itself.

seanz0rz

yes but people that park their car and remove componets from under the hood are crazy... my uncle does this with his POS trashed 90 corolla. he also puts the club on... hes afraid someone is going to steal it. like it would be the end of the world anyway...

anyway, i have an ignition cut out switch under the dash of my honda. its great.

i feel i really need one on the 4runner, looking to install one this summer.

CJM

I'm crazy to remove the efi fuse? Who cares, without it they aint going nowhere fast.

midiwall

I don't think it's crazy.... But I think it draws attention for someone that may be thinking about nabbing your truck. "Hmm, why does he do that every time???"

My feeling about cutoffs is the same as alarm systems. If someone wants YOUR rig, they're gonna take it. It's nothing for someone to get your truck with a flatbed. The only thing that cutoffs and alarms are good for is as a deterrent, which is something, but you still end up with a busted window/lock/steering column before they give up. I guess you still have the rig though...

YotaFun

If I know I will be keeping the Runner somewhere for a while...
And I am really parinoid...
I will turn the the wheel all the way in some direction, Put it in 4Low and the club on, this keeps it from getting towed
(have yet to install a cut off swtich)
I sometiems have to travel to parts of NYC that I really wouldn't like to...

4Crawler

iTrader: (3)

Why not cut the AFM control signal to the circuit opening relay with a switch:
http://www.4crawler.com/4x4/CheapTri...shtml#FuelPump



That way the engine would start normally, run a little but then die as the fuel pressure dropped. I imagine that would discourage most thieves.

art

I put a switch on the hot side of the fuel pump similar to this one,except mine is an on-off, on my truck 17 years ago. I installed it a few days after buying the truck. No problems. I think mine is a cole-hearse brand but it looks just like this one. http://www.wiringproducts.com/index....tml&lang=en-us

L33T35T 4Runner

as to which side, positive or negative, it really doesnt matter. I suggest using a relay, as if you ran the normal power wire to the switch, you would have to run that high amperage through the switch, and also you would have to lengthen the wire, and you might lose some voltage going to your pump, causing problems in the future.

I vote:
whichever side is easier, neg or pos
install with a relay

Crazychopstick

So as long as the switch is the correct amperage then a relay is NOT needed correct?

What kind of relay should I be looking for? Found at regular Autozones?

midiwall

Correct. The only other thing that I wold add is that if you;re JUST going to go wit a switch, then spend the money on a GOOD one. If the switch should fail, then you're stuck (well,. until you jump across it). Also, a cheap switch could "arc" under a close-to-capacity load. This is where a spark will occur within the switch, that'll shorten the life of the switch.


Yeup. The standard ones are 20amp, the heavy duty's are 30amp. If you have the capability, you should measure the current draw of the fuel pump to be sure, but a 20amp _should_ be okay. If you have any doubts, then buy the 30amp.