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Fuel pump cutoff switch
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Wildthings
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PostPosted: Wed Dec 20, 2017 9:40 pm    Post subject: Re: Fuel pump cutoff switch Reply with quote

Running the ground wire off of Pin # 86 on the fuel injection relay to a kill switch would kill the FI relay and indirectly the FP relay.

Current track #17 as per this wiring schematic:

https://www.thesamba.com/vw/archives/manuals/1985_...agrams.pdf
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narendra.vw
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PostPosted: Thu Dec 21, 2017 6:15 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

Thoughts I like to share,

Any van having a remote electrical central locking unit this should work.

Every unit has a Siren which goes off to let the Owner know(or the surrounding) someone is trying to get inside.
once Siren goes off means it has got power from the battery.
Using this power, connect it to a relay & send it to the additional locking actuator provided.
the actuator rod which moves in & out should be connected to a spring loaded pull & push switch(brake switch) which in turn power the 'fuel pump'.
In normal usage by using proper remote siren does not go off means no power. The spring loaded switch sits back in 'ON' position & power to pump is continuously supplied.

Am I missing something here. Smile
Actuator
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davevickery
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PostPosted: Thu Dec 21, 2017 12:51 pm    Post subject: Re: Fuel pump cutoff switch Reply with quote

I just have a simple kill switch, but a remote control one could be better hidden.
https://www.ebay.com/itm/MSD-12v-on-off-normally-c...51a9a59d5a There are a few different versions of these on ebay.

If you have a stock engine the FP relay is under the engine lid. On a subi it is under the seat. So just cut the power wire going to the relay and hook up this remote controlled switch.. Add a lock to the engine lid or rear seat and they won't even be able to get in there to try to bipass it.
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candyman
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PostPosted: Mon Jan 15, 2018 4:27 pm    Post subject: Re: Fuel pump cutoff switch Reply with quote

So due to this thread i am rewiring my kill switch. Following Marks advice in this thread, I want to clarify that I am doing this right. He claims to add a switch to the FP relay ground not the ground on pump itself. Mine is on the pump ground itself with likely an underpowered switch.
On my 87 it looks like the ground wire for the FP relay is the big red wire leaving the FP relay box and terminating on a lug in the wire box on the lefthand firewall. As far as I can tell that wire is the ground as both relays are tied together coming off terminal 30 from each relay. If this is correct that is wire that I want to add my switch to? Incidentally, that is same wire that should be fused to save a meltdown in the event of the PS switch shorting.
Just want to clarify that I have this right. And thanks to this thread I had no idea that my current set up could have left me dead in the middle of the road if my switch were to fail. Which is likely since it is not 8 amp rated
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pomfritz
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PostPosted: Tue Jan 16, 2018 12:26 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

In your drawing is this relay shown one that you added by the fuel pump?

fxr wrote:

Below is the circuit of what I did. It just needs one wire running from the relay to the switch - wherever you might put that. Here's a link to the switch I used, almost invisible when installed on a black background:

https://www.frys.com/product/1945881

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dobryan
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PostPosted: Tue Jan 16, 2018 5:40 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

candyman wrote:

On my 87 it looks like the ground wire for the FP relay is the big red wire leaving the FP relay box and terminating on a lug in the wire box on the lefthand firewall.


To me that does not sound like any ground wire that VW used. Big red seems like a positive source, and that lug inside the 'wire box' on the firewall is full time 12V+.

Be careful.....
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danfromsyr
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PostPosted: Tue Jan 16, 2018 7:05 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

you are most definitely NOT right.
that red wire and the post are tied directly to the back of the Alternator and the large lug on the starter.



candyman wrote:
So due to this thread i am rewiring my kill switch. Following Marks advice in this thread, I want to clarify that I am doing this right. He claims to add a switch to the FP relay ground not the ground on pump itself. Mine is on the pump ground itself with likely an underpowered switch.
On my 87 it looks like the ground wire for the FP relay is the big red wire leaving the FP relay box and terminating on a lug in the wire box on the lefthand firewall. As far as I can tell that wire is the ground as both relays are tied together coming off terminal 30 from each relay. If this is correct that is wire that I want to add my switch to? Incidentally, that is same wire that should be fused to save a meltdown in the event of the PS switch shorting.
Just want to clarify that I have this right. And thanks to this thread I had no idea that my current set up could have left me dead in the middle of the road if my switch were to fail. Which is likely since it is not 8 amp rated

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MarkWard
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PostPosted: Tue Jan 16, 2018 7:16 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

It's not 100% but as a rule VW used brown wire for grounds. I am on my phone, but I recall posting what wire should be interrupted earlier.
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candyman
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PostPosted: Tue Jan 16, 2018 8:29 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

Ah yes, got it now
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candyman
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PostPosted: Tue Jan 16, 2018 4:59 pm    Post subject: Re: Fuel pump cutoff switch Reply with quote

Not hijacking this thread, but thought I would update for anyone following along at home. My van is an 87 so the wire diagram mark referred to earlier in this thread is for an 85. On my 87 the ground wire for the fuel pump relay is the brown/red wire coming off the relay. I think it was terminal 85, but not exact as its not in front of me at the moment. This ground wire terminates along the drivers side firewall with other ground wires.
As far as amps are concerned, i measured the amps at the fuel pump ground and the relay ground. the fuel pump ground wire measured 2.8 amps while the fuel pump relay ground measures .30 amps. This was measured while van was idling. My rocker switch is only rated to 2 amps so I am glad this thread came up and saved me from a switch failure down the road. Thanks Mard Ward for the advice on relocating the switch to the relay ground as opposed to the fuel pump ground itself.
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fxr
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PostPosted: Tue Jan 16, 2018 6:05 pm    Post subject: Re: Fuel pump cutoff switch Reply with quote

pomfritz wrote:
In your drawing is this relay shown one that you added by the fuel pump?

fxr wrote:

Image may have been reduced in size. Click image to view fullscreen.


Yes, that relay is added directly beside the fuel pump.
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Sodo
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PostPosted: Thu Apr 23, 2020 12:12 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

candyman wrote:
the fuel pump ground wire measured 2.8 amps
.... This was measured while van was idling.
My rocker switch is only rated to 2 amps
.....
so I am glad this thread came up and saved me from a switch failure down the road.


Well what you did is now more proper.....but you did not avert catastrophy.
A 2A switch is rated to make/break a full 2Amps perhaps thousands, or tens of thousands of times.
It could probably switch 2.8Amps for a very long time, tens of years.

It can handle much more than 2 amps just carrying current if NOT make/breaking the live connection (sparking).

To wear out this killswitch.....you'd have to switch it off under load while the ignition is on (engine running).
And you'd have to switch it ON under load (while cranking the starter motor).
This, THOUSANDS of times.

That's not how a security kill-switch is used.

In normal usage it's turned on/off when the ignition key is OFF (dead).
It never 'sparks' across the terminals.
It's a 'static' usage, wherein the current carrying capacity FAR exceeds the rated make/break capacity.
Consequently; a 2A switch would last appx "FOREVER".
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elkzilla
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PostPosted: Mon May 02, 2022 12:34 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

Thanks to info from this thread I'm very happy with where I interrupted ground on my westy fuel pump relay...works great. I cut the ground wire on 86 on the right relay, but due to zero slack I had to solder the two black extension wires.

Edit: I intend to re-do this with better / tougher wire. Thanks.

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Last edited by elkzilla on Mon May 02, 2022 4:05 pm; edited 1 time in total
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DuncanS
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PostPosted: Mon May 02, 2022 5:12 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

Please, please, guys, do NOT use lamp cord. The insulation is nowhere near as good as marine wire and the untinned copper strands just love to become oxidized, turn black and carry no load. Lamp cord is designed to be used indoors, not in an exposed-to-road-crud environments. Yes, this:
https://www.amazon.com/Ancor-Marine-Grade-Primary-...2837272344 is more expensive, but it won't strand you in East Overshoe scratching your head. Isn't that worth a couple of extra bucks? And don't forget, T3s like to be treated well. If they feel they have been disrespected, they have ways of telling us so; usually with something we don't want to hear.

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Ahwahnee
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PostPosted: Mon May 02, 2022 7:23 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

X2 on no lamp cord.

Additionally, if interrupting a ground I just use a single wire run to the switch and then the other side of the switch gets a short lead to any nearby ground spot.

The relay should be fine but interrupting at the pump is a much shorter run -- though possibly not as secure if a thief is willing to crawl under the van (seems unlikely).
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crazyvwvanman
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PostPosted: Mon May 02, 2022 7:30 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

In this case a single wire is NOT suitable because it isn't a true ground that is being interrupted by the switch.
What is being interupted is the fuel pump relay enable signal from the ECU.

I have some concerns with this overall approach as making a wrong move could damage the ECU though that isn't too likely.

Mark

Ahwahnee wrote:
X2 on no lamp cord.

Additionally, if interrupting a ground I just use a single wire run to the switch and then the other side of the switch gets a short lead to any nearby ground spot.

The relay should be fine but interrupting at the pump is a much shorter run -- though possibly not as secure if a thief is willing to crawl under the van (seems unlikely).
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DuncanS
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PostPosted: Mon May 02, 2022 9:23 am    Post subject: Re: Fuel pump cutoff switch Reply with quote

Considering Mark's concerns about sending a bad voltage to the ECU, maybe we should rethink using the fuel pump as a theft deterrent.

I have an invisible switch on the dash with grounds the tach wire. When deployed, the car will grind and grind, but not start, which is the same effect you get with taking the fuel pump out of the game. For me, this is far better than having no noise at all when the ignition is bypassed. The thief, may think, "Just another crappy VW, and I'll try a different one."

My main concern about the fuel pump is having a switch which will remove 100% of electrical power everywhere. Remember, even with the key off, the alternator, starter and AC have serious juice back there all the time. For this reason I did this:
Image may have been reduced in size. Click image to view fullscreen.
on the ground.

And as extra theft security, but weak, there is this mode.
Image may have been reduced in size. Click image to view fullscreen.


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