[hessank]

I am thinking of installing a 'Kill Switch'. The two most common options are cutting power TO the Starter or the Fuel Pump.
One additional option is a 3-way switch on either of those two pieces of equipment with power to the Horn in the Off position. So, someone tries to start the car and gets a blaring horn. Hopefully, they move to the next car.

I am not trying to add a failure point. Afterall, I would know where the switch is and restitution would be just a matter of connecting 2 wires. Car thefts/car jacking are both on the rise. I just want to keep my car safe.

I don't want one of those electronic remote battery disconnect switches because I don't want any electronics.; that would be adding a failure point. Besides, my battery/leakage does not need a granny/babysitting monitor. I just a plain manual toggle switch, hidden of course

What are your thoughts?

[worf]

there are a lot of diabolical ways to mess up a 928 with one wire… lol.

manual transmission?

switch instead of relay bridge for auto-lockout relay. Make it impossible to find by wiring it from the back of the panel.

if auto, wire another switch into the auto-lockout relay circuit.

switch on EZK, LH, or FP relay switch-side.

I wouldn’t recommend messing with ignition switch wiring. better to “mess” with the low current switch-side of relay.

And if you do something like that make a wiring diagram and keep it with the service records or never sell it. (‘cause when you wire up stuff like that you go on the hit list for the technician that has to reverse engineer what you did for the next owner…)

[hessank]

there are a lot of diabolical ways to mess up a 928 with one wire… lol.

manual transmission?

I wouldn’t recommend messing with ignition switch wiring. better to “mess” with the low current switch-side of relay.

Thank you.
Yes, manual trans
Good point about FP (switch side of relay). Noted

[N_Jay]

An easy one is switch to ground on the hot side of the ignition.
No matter how the thief gets power to the ignition circuit the fuse gets blown
Same could be done on the fuel pump circuit.

[worf]

An easy one is switch to ground on the hot side of the ignition.
No matter how the thief gets power to the ignition circuit the fuse gets blown
Same could be done on the fuel pump circuit.

‘prolly want to very carefully scrutinize the wiring diagram before attempting a mod like that. Porsche didn’t put fuses in a 928 for every possible way someone might deliberately or accidentally short battery power to ground. It’s more likely to release the ‘factory-installed smoke’ in a harness IMO than to blow the fuse you think it will blow.

“Turning off” the fuel pump or either of the engine control units by interrupting ground at a relay socket will be sufficient.

If a thief is smart enough to look at the fuse panel diagrams for the MY 928 in question (they’re are many variations) and bridge the FP, LH, EZK/EZF and starter-lockout relays… then they’re going to take the car no matter what you do :)

You could also wire a remote switch into one of the crank position sender signal wires at the EZK plug and then hide it somewhere. No CPS, no start.

That’s actually a nicely reversible mod since you can easily depin the ECU connector and then don’t even have to cut wires. And it could be completely stealthed.

Hmmm… that switch’s wires would need to be shielded with the shield junctioned to the rest of the harness shielding…

… so.. yeah, naw, switching the CPS signal not the way to go.

[N_Jay]

An easy one is switch to ground on the hot side of the ignition.
No matter how the thief gets power to the ignition circuit the fuse gets blown
Same could be done on the fuel pump circuit.

‘prolly want to very carefully scrutinize the wiring diagram before attempting a mod like that. Porsche didn’t put fuses in a 928 for every possible way someone might deliberately or accidentally short battery power to ground. It’s more likely to release the ‘factory-installed smoke’ in a harness IMO than to blow the fuse you think it will blow.

“Turning off” the fuel pump or either of the engine control units by interrupting ground at a relay socket will be sufficient.

If a thief is smart enough to look at the fuse panel diagrams for the MY 928 in question (they’re are many variations) and bridge the FP, LH, EZK/EZF and starter-lockout relays… then they’re going to take the car no matter what you do :)

You could also wire a remote switch into one of the crank position sender signal wires at the EZK plug and then hide it somewhere. No CPS, no start.

That’s actually a nicely reversible mod since you can easily depin the ECU connector and then don’t even have to cut wires. And it could be completely stealthed.

Hmmm… that switch’s wires would need to be shielded with the shield junctioned to the rest of the harness shielding…

… so.. yeah, naw, switching the CPS signal not the way to go.

Get out a wiring diagram and check first, but the blown fuse is easy, and unexpected by a thief.

It is also a second line of defense should her find the switch.

[worf]

Get out a wiring diagram and check first, but the blown fuse is easy, and unexpected by a thief.

It is also a second line of defense should her find the switch.

I agree that it’s a second line of defense. And, *in theory* it’s a good idea other than deliberately shorting power to ground is usually a bad idea even in a fused circuit. But, since it was your idea, I think it incumbent on you - not me - to dig through the unique-to-1989 928 wiring diagram and figure out - and warranty - the notion that it won’t smoke the dash harness on its way to the fuse panel.

Interrupting ground on the switch-side of a relay is very safe and very contained.

[hessank]

I just want to use the KISS Principe here (Simple, Safe, not Stupid). I also don't want to create an error situation for myself and having to find a blown fuse in wiring. That's why a hidden Toggle Switch is attractive.

Remember, these car thieves are breaking into cars for a quick getaway (in older cars it'll be a screwdriver in the Ignition etc). They also want to ship them to Africa as whole as possible, that's where the big $$$ is.

As a matter of fact, my cousin works in Zimbabwe and goes to Ghana as well. There are high end and older sorts cars there STILL with Canadian and US plates. The 'NEW' owners don't even bother to change the plates and the Gov/Police there don't give a F#@*

Thanks for all the comments

[hessank]

I was in a Jeep a while ago (that's when I got the idea to put something in my car) and it required 2 hands to start it.
You had to press a momentary button button (hidden) and then turn the key. I thought that was brilliant.

Most of us have an unused button; the High Intensity Washer switch

[worf]

Most of us have an unused button; the High Intensity Washer switch

Hmm… yes, that’ll work nicely.

[hessank]

Thanks, I thought so.
So, playing along, is it the Yellow ignition wire I put across this switch?
Would it handle the juice momentarily?

[worf]

So, playing along, is it the Yellow ignition wire I put across this switch?
Would it handle the juice momentarily?

How big (thick) is the yellow wire? How thick are the wires going to the HI washer switch?

But, since you are talking about the ignition wiring, that means you are proceeding down N_Jay’s path and that means I’m out of this discussion. Good luck.

[hessank]

Not so fast Worf. I was just asking a question and thank you for all your ideas
I am 90% decided on the path towards a Toggle switch and the fuel pump.
3/$10 3-Way Toggle Switch arriving tomorrow from Amazon

Which is the most accessible option?
Wire to the fuel pump relay or from relay to the pump?

please and thank you

image.png

[worf]

The wires you've highlighted are on the *switched* side of the relays not on the *switchING* side of the relays.

Your 'yellow' and 'green' wires carry big current (look at the fuse ratings) and will fry any small switch and any small wire. That's why those current paths have a relay and BIG wires on the switched-side. A relay uses a low-current circuit to activate a high-current circuit specifically to avoid passing high (heat-generating) currents through hand-operated switch gear. This avoids a great many 'sins.'

Relay terminal and bus guide:
87: 12v, switched, high-current output.
30: 12v high-current input
86: 12v switching signal for relay to 'turn-on' high-current output
85: switching ground path for the 86 switching current.

31: Ground Bus
30: Battery 12v constant bus.
15: ignition-on 12v bus

If you look at the diagram the simplest path is EZK XXII 85 to 31 (ground). This is the path that I might use for a 'kill switch.'

Alternatively, LH XXV 85 to the EZK(*) would result in cleaner wiring since you can depin that wire at the EZK connector and thus not actually cut any wiring to get your 'switch' into the circuit. (You can depin the relay sockets, but it's a bitch.)

In either case, what *I* would next locate is a small low-current (1 or 2 AMP) 'latching' relay. I don't know exactly what they are called... you want a relay where the switching side is activated with a momentary switch but will stay 'switched' as long as current is flowing through the 'switched' side. They exist, but, like I said, I don't remember what they are specifically called. In any case, this would allow you to crank the engine to start while holding the 'switch'(**) down, will keep the relay 'active' while the engine is running, but will then 'open' the circuit again when you stop the engine.

You could also use a simple 'toggle' switch, but then you'd need to remember to turn it 'off' whenever you want theft prevention active.

(*) The EZK switches the LH relay on when it sees a signal from the CPS.

(**) I'd recommend just getting a momentary switch and 'hiding' it somewhere rather than using the washer switch. The washer switch is too easy to 'feel' for.

[N_Jay]

Hidden GPS trackers are nice for tow-awsy thefts.
Smart theives will cut the battery cable, so add a small gell cell to get a couple of days of tracking.

[hessank]

Thanks Worf.
Wow, not as simple (to do it correctly and safely) as I thought. Hence, my plea for help.
Thank you. I know what to do now.

[hessank]

Thanks Worf.
Wow, not as simple (to do it correctly and safely) as I thought. Hence, my plea for help.
Thank you. I know what to do now.

Thanks Jay.
Not too easy (maybe impossible) to get under my car without a jack to cut the main cable.
My Koenig-Specials is low to the ground

[worf]

Wow, not as simple (to do it correctly and safely) as I thought. Hence, my plea for help.
Thank you. I know what to do now.

As wiring mods go, it is pretty simple.

I’ll see if I can figure out what the right relay type is called over the next week as it would be nifty to have a couple on hand here.