SPDT Fuel Pump/Horn Kill Switch
 

Whats up everybody?

So ive been doing a bunch of research here on the forum and searching on the internet, how i can wire up a SPDT switch to cut the fuel pump, and sound the horn when activated. The general consensus on how to do this is to have the SDPT Switch, with one side connected to the power wire from the COR to the Fuel pump, the middle port connected to the Other side of the COR wire, and then the Opposite side would be connected to the horn.

"Originally Posted by abecedarian https://www.yotatech.com/forums/imag...s/viewpost.gif
SPDT toggle, rated 15 amps, interrupting the fuel pump this way:
- cut the wire to the fuel pump and connect the fuel pump side to one end of the switch and the other end (should be coming from the Circuit Opening Relay) to the center terminal of the switch... and connect the horn to the other end of the switch.

If the switch is set for the fuel pump to work, the truck starts. If the switch is set the other way, the horn goes off when the thief tries to crank it over or tries bump starting it and the AFM turns the COR on."

BUT I have a couple questions on this. I have an aftermarket horn, with a relay setup. Should i attach the horn wire to the same signal wire that activates my relay for my aftermarket horn? or just attach it to the wire that sends the power to the horn?

AND should i just use a relay for this as well? some people online were saying you should use a relay for a kill switch setup like this, and not just a SPDT swtich.

I have an attached picture of what i think should be the setup without a relay.. Im working on the relay diagram as i am a bit confused with using the Relay and a SPDT switch at the same time

Thanks. Oh BTW I have an 85 4runner with a 22re and EFI. So i have the electrical fuel pump

Thanks.

It is your project doing it either way will work .

Energizing the coil on relays will always take less current then powering the load direct through a switch

Carry extra parts with you .

Having easy access to the switch really defeats the whole idea of the kill switch

It never fails these kill switches seem to fail at the worst possible time and place .

Would it be better to use a relay or would a basic SPDT switch work fine? And of course this kill switch would be very very hard to find for any wannabe thieves.

Ah yes an extra switch would be a smart idea if this one fails at some point. Would that be a good reason to put in a relay for this whole project?

Great idea that I had always wanted to do but is lower on list of priorities.

To the signal wire (the "OR" option) that energizes the relay. This will require less current draw on the COR contact.
Re: the probability of switch contact failing, I would use a double-pole double-throw switch. Just connect the contacts in parallel. the chances of any 2 contacts failing at the same time is slim.

However, the schematic of your aftermarket relay looks wrong:
You have a horn switch going to pin 85 to provide ground (stock horn switches ground to horn), AND you have the after market "horn button" that goes to pin 86.
Do you mean you have to push two buttons in order to sound your horn?
https://cimg9.ibsrv.net/gimg/www.yot...04ccb48ff7.jpg

OR your horn switch circuit has been bypassed. If the latter, schematic should show pin 85 as going directly to ground, not to horn switch.

Ah okay good idea on the DPDT switch. Do you know if another relay would be useful in this scenario? Or would it just be over kill?

haha ah this isn't my actual horn diagram, i just pulled one offline for reference. I just needed to know if I should wire it to the power wire to the horn, or to the switch side of the horn relay.

With a DPDT switch you would essentially be running two of each wire? Pretty much like two SPDT switches, just mashed into one?

Unless we know exactly how your system is wired, OR you have a fire extinguisher handy (LOL!) we would not know for sure.

Exactly. The switch will be critical to operation of the engine so I really like to use DPDT.

I think your both a little confused.

You just connect both contacts on the switch to the one wire.

You can of course run double wires but it is not needed

Your hoping to prevent a switch failure with two contacts the chance of failure is greatly reduced as compared to one .

I am glad I live where the keys are in the ignition most of the time.

... a picture paints a thousand words...

https://lh3.googleusercontent.com/7_...=w1214-h528-no



Yep... half hour from time truck goes missing and my truck could be south of the border.

Ahhh okay yes no need for two wires but just have two connectors, in the event of one side of contacts failing. Thanks so much for the picture! This will help me out a lot while wiring!

Do you guys think a 15 amp toggle would be sufficient to handle the load of the fuel pump power? From my research it seems like this should be enough.

Now the question is where to place it.. Hmmmm... DM me any sneaky ideas!

Okay Guys so i pretty much have this all setup, but i cant get the horn to go off when i turn the key! Heres a diagram of my aftermarket horn setup. The only difference is that i think my Ground cable was bad so the PO ran a ground cable from the harness to the horn. Ive tried connecting the horn side of my kill switch to Pin 86 but it still wont turn on when i turn the key.

Im wondering if the switch is just not grounding it? Because the rest of the system works, turning on and off the fuel pump.

My feeling is that its not making a complete circuit for the horn to blast off.


https://cimg1.ibsrv.net/gimg/www.yot...1375fe2854.jpgmy horn relay

Sending 12V to pin 86 of your after-market horn relay will not work because the stock horn circuit relies on switched ground. Horn button on steering wheel grounds pin 85 while there is steady 12V on pin 86 of relay.
IF your stock horn wiring is unmolested and you're using after-market setup above, you should connect the "horn side of your kill-switch" to positive side of the after-market horn. Need to ensure that the horn will not overload your COR.

TO BE SAFE, because of the switched ground nature of the horn, while the "horn side of the kill switch" provides 12V in Kill mode, I think it would be better to insert your kill-switch between main relay and the C.O.R.

Here's how horn circuit works : https://www.yotatech.com/forums/f116.../#post52381275