DIY: Honda FIT Kill Switch

[Veen]

###### EDIT ######
Based on my experience and the advice from BaltotheWolf, I don't recommend using the Igniter Fuse method for the Honda FIT. About 15% of the time it causes "dieseling" which prevents the motor from turning off and probably causes damage to the engine over an extended time. I'll update this thread when I have found a new solution for the FIT.
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Just finished my kill switch for my FIT. I don't have a lot of miles on it so I can't say for sure it won't cause trouble, but it uses the ignition coil fuse, which I think is same as key off kill. Anyway, here's how I did it:

Disclaimer: Kill switches are dangerous, I am not an automotive expert, I may have royally f***ed something up with my car, proceed at your own risk.

Parts:
Momentary switch: any, can be low current
Toggle switch: any, can be low current
Relay: Should handle 15A, I used CP1SA-12V-X
Fuse Tap: Got it from Autozone, mini, low profile kind
Wire/solder/connectors: Use what you have

Tools:
Wire Stipper
Crimper
Soldering Iron
Zip Ties

Overview:
Reconfigure Fuse Tap
Wire Fuse Tap to Relay and switches
Locate and remove IG COIL fuse
Install modified fuse tap

Reconfigure Fuse Tap:
The fuse tap is meant to create another circuit in parallel with a given fuse, instead I want it to interrupt the circuit the fuse is protecting (and keep using the fuse for protection) when I cut it with the relay.


Open the fuse tap carefully with a razor blade, I had to remove the heat shrink off the wire.


Remove and flatten the small fuse blade that is meant for the original circuit. This is hard to do without wrecking it.


Solder a heavy gauge wire to flattened fuse blade and reassemble the fuse tap with the wire sticking out. I had to remove bits of the plastic housing with a razor to get it to close properly. I used super glue to hold it together again.



Wire Fuse Tap to Relay and Kill Switches:
Now I had the top fuse position on the fuse tap open to accept the ignition coil fuse and two wires that need to be closed for the ignition coil circuit to be closed. I wired them to the Normally Closed taps on my relay so that if anything happened to my kill switch wiring, it would default to closed. Only a catastrophic relay failure should cause this to disrupt normal function of the FIT.
I put a toggle switch and a momentary switch in series so that I can disable to the kill switch if someone else is driving the car or the kill switch button malfunctions and sticks on.
I installed the relay on the fuse bay door and put the toggle switch in one of the extra button slots near the VSA disable button.



Install Modified Fuse Tap:
I removed the IG COIL fuse and put it in the top slot of the modified fuse tap and installed the whole thing in the original fuse location.


The relay needs a ground connection on the coil side to activate, and I found one that holds the fuse panel in place.



That's it! The install is pretty simple, and should be easy to remove as well.
The toggle switch on the far right is the enable/disable.


And here's the momentary switch on the shift knob.


I'll update this thread after I put some miles on it and verify it works.

[Veen]

I've put about 25 miles on the car since the install. So far I have not had any engine problems except for when I forget that the button actually works and start playing with it

I had to get an inspection today and didn't get any trouble from the auto shop or get any feedback of something being horribly wrong. It's only been on for a few miles so that doesn't necessarily much.

It does seems like it takes a second longer for the engine to shut down when using the kill switch vs key off, I'll have to investigate that more. I do like that the ultragauge reports properly every time now with the engine killed. Before, when I would key off, the ultragauge would stop reporting trip and short trip MPG about 50% of the time.

[Fat Charlie]

Yeah, I can't wait until mine's done. My UG comes fully back up less than 5% of the time for EOC.

[marky899]

Hi,

Im from the UK. Im loving this forum

Im going to do this mod to my car but iv read that it may be best to do it from the fused that controls the injectors to cut them off.

Am i right in thinking that i will need an Normally Open switch? So when i press it, it makes contact and allow current to flow?

Also i like how you added the toggle switch to enable/disable the function, i think i will also be adding this. May put a cool fighter yet switch for the enable/disable, so it cant be accidentally pressed.

Thanks

[California98Civic]

Nice idea, OP. I like the write-up too. Thanks.

Originally Posted by Fat Charlie

Yeah, I can't wait until mine's done. My UG comes fully back up less than 5% of the time for EOC.

Depending on how you set it up, you might want to check the setting for the UG itself. For a longtime, my UG cut out for several seconds much of the time when I cut the injectors. Then I learned here about a settings change to how often it attempts a restart or something (search the forum). Fixed it.

Originally Posted by marky899

... Im going to do this mod to my car but iv read that it may be best to do it from the fused that controls the injectors to cut them off.

Am i right in thinking that i will need an Normally Open switch? So when i press it, it makes contact and allow current to flow? ...

I don't know what you are driving, but on my old Civic, I cut into the ground wire for the fuel injector relay. Cuts the injectors off immediately. My toggle is normally closed, switching to off is to open the circuit. I have used it for maybe four or five years without trouble (though I have worn out one switch and broken wires).

[marky899]

Originally Posted by California98Civic

I don't know what you are driving, but on my old Civic, I cut into the ground wire for the fuel injector relay. Cuts the injectors off immediately. My toggle is normally closed, switching to off is to open the circuit. I have used it for maybe four or five years without trouble (though I have worn out one switch and broken wires).

Hi, thanks for the reply.

Im driving a Renault Clio 1.2 16v. Cheap little car

Well iv just bought a few items off ebay.

5 pin 30A rely
in-line fuse holder
normally open switch
16 gauge wire

So you idea about cutting into the injector relay earth, im guessing i wont been needing the relay i bought.
Would you recommend still using the in-line fuse and the normally open switch?
Im a noob when it comes to car electrics and electronic components.

thanks

[Veen]

Originally Posted by California98Civic

Depending on how you set it up, you might want to check the setting for the UG itself. For a longtime, my UG cut out for several seconds much of the time when I cut the injectors. Then I learned here about a settings change to how often it attempts a restart or something (search the forum). Fixed it.

Yes, the power off settings on the UG will help this. I had the smart problem on my FIT.

Originally Posted by California98Civic

I don't know what you are driving, but on my old Civic, I cut into the ground wire for the fuel injector relay. Cuts the injectors off immediately. My toggle is normally closed, switching to off is to open the circuit. I have used it for maybe four or five years without trouble (though I have worn out one switch and broken wires).

I don't know how much current flows through the injector ground, if it's low enough, a normally closed momentary switch would be okay. I always think of what will happen if my mod fails while I'm driving. If my mod will "brick" my car without serious work to remove the mod, I'm not interested. In my case, I wired the power side of the relay normally closed, so applying current to the control side of the relay will break(open) the circuit and kill the ignitors.

This way, if the my switch fails, I won't be able to use the button to kill the engine. No big deal, I get home safely and fix it. The relay is specifically designed to switch high current loads 1,000's of times so it is less likely to fail. But if it does, I can remove my modified fuse tap, and install the fuse on its original location and be on my way again. I don't even have to get out of the car. I wouldn't want to be trying to splice or solder wires together in my engine bay on the side if the interstate in rush hour. Design for failure.




I have been thinking about changing my kill method. I'm not getting super reliable kills. Probably about 15% of the time, the RPMs hover at 200 or so and the car starts back up even though I'm in neutral with the clutch in. I'll probably start looking in to the injector circuit, or taking in to the key circuit.

[Baltothewolf]

Veen, I would recommend not continuing to kill your car with that method. Your vehicle is doing what is called 'dieseling' in essence, your car is spraying fuel and detonating it without spark. Very unhealthy. Go the injector method, it's tried and true.

[California98Civic]

You should not need and won't want the fuse holder if you go the route I did. I recommend you consider what Veen and Balto said above too. Most importantly, be prepared to experiment and the experience failure. Don't cut into wires without a schematic for the wiring system and consider how a given wire might serve several systems. For example, when I cut my switch, it also cuts the fuel pump. No problem, since I am cutting the engine. But if you have an alarm or a car-immobilizer security system, it could get dicey. Plan carefully. Get a wiring diagram. Always try a reversible version of the mod before a permanent one.

[marky899]

Iv just had a thought.

Would it not be a good idea to just connect into the actual key switch wiring so when the Normally open witch is closed, it replicated turning the key to off mod and when released, it replicated turning it back on.

Iv said before, i know very little about car electrics so yes this method is probably stupid somehow. haha.

The method i do want to follow is the one that involved the fuse for the injectors. believe it was from a thread by bbjsw10.
Cannot add link due to not having enough posts.


Any downsides to this?