Installing a theft relay.

Doug Larsson · Jan 26, 2017

I purchased one awhile ago and redid my ignition harness connection and thought I would do this also. I'm looking for a second set of eyes to make sure I'm looking at this correctly.
Ignition black wire to black relay wire .
Yellow ignition wire to orange relay wire.
Blue relay wire to ground.
Red relay wire to negative side of switch.

747mopar · Jan 27, 2017

Take the time to understand the relay and what it does and you won't need a diagram. Looking at this picture 85 and 86 will be your signal to engage the relay (12V - and +), it doesn't matter if you use positive or negative to do the switching but generally it's the positive. In cases where your concealing the switch in tight spaces it's handy to use the negative because all you need is 1 wire with the other side of the switch grounded.

Terminal 30, 87A and 87 are just a switch inside the relay. Using 30 as the incoming power you just select whether you want a normally open or closed contact. The drawing illustrates the relay in it's natural state (de energized).

Now to make it work you simply connect your theft switch to 85 or 86 (1 grounded and 1 getting the signal from your switch) and interrupt your starter wire or coil wire with 30 and 87.

The nice thing about this is you can literally use just about any existing circuit as a theft switch or install your own. You could use your windshield washer switch by simply running a wire from your washer feed to one side of the relay..... car won't start unless your pushing the washer button while turning the key. In most cases people just hide a switch.

68gtxman · Jan 27, 2017

747mopar said:
Take the time to understand the relay and what it does and you won't need a diagram. Looking at this picture 85 and 86 will be your signal to engage the relay (12V - and +), it doesn't matter if you use positive or negative to do the switching but generally it's the positive. In cases where your concealing the switch in tight spaces it's handy to use the negative because all you need is 1 wire with the other side of the switch grounded.

Terminal 30, 87A and 87 are just a switch inside the relay. Using 30 as the incoming power you just select whether you want a normally open or closed contact. The drawing illustrates the relay in it's natural state (de energized).

Now to make it work you simply connect your theft switch to 85 or 86 (1 grounded and 1 getting the signal from your switch) and interrupt your starter wire or coil wire with 30 and 87.

The nice thing about this is you can literally use just about any existing circuit as a theft switch or install your own. You could use your windshield washer switch by simply running a wire from your washer feed to one side of the relay..... car won't start unless your pushing the washer button while turning the key. In most cases people just hide a switch.

View attachment 390937

I agree, and you nailed my switch of choice too - the washer spray button. I picked it because I will never use it, it is hidden in plain sight, and I can still start the car with one hand. Only one mechanic has ever figured it out so far.

PurpleBeeper · Jan 27, 2017

Another way to do basically the same thing is to splice in an on/off switch into the blue ignition wire. You can crank it, it will "try" to start, but won't run.

Doug Larsson · Jan 27, 2017

PurpleBeeper said:
Another way to do basically the same thing is to splice in an on/off switch into the blue ignition wire. You can crank it, it will "try" to start, but won't run.

That seems a lot easier way than to install a relay I have and on/off switch i just purchased. It's safe to do it correct ?

68gtxman · Jan 27, 2017

PurpleBeeper said:
Another way to do basically the same thing is to splice in an on/off switch into the blue ignition wire. You can crank it, it will "try" to start, but won't run.

Except that circuit may carry more current than the switch is rated for and could cause a meltd switch or non-start condition.

Doug Larsson · Jan 27, 2017

68gtxman said:
Except that circuit may carry more current than the switch is rated for and could cause a meltd switch or non-start condition.

That's very true it's a 15amp switch but I'll probably go with the relay I purchased most likely.

A383Wing · Jan 28, 2017

another way with just a toggle switch is to connect one side to the negative side of coil and the other side of toggle switch to ground....hide the switch and it will never start when switched on, can't even hot wire it

Dennis H · Jan 28, 2017

Up your insurance, and park as smart as possible. Use a car cover. No way to prevent theft. Tow trucks trump all.

Doug Larsson · Jan 29, 2017

Dennis H said:
Up your insurance, and park as smart as possible. Use a car cover. No way to prevent theft. Tow trucks trump all.

Thank you for your advice but I'm looking for electrical advice not real world go find another forum for that.

Lionized · Jan 29, 2017

I've been considering using my cigar lighter.

Nacho-RT74 · Jan 29, 2017

Once I though to isolate the ECU from chassis ground, switching it on/off from interior ( or even remotelly wireless ). Pretty much easy to do it, just inserting plastic fasteners into the cowl panel or wherever you have your ECU mounted, and eyelet terminal attached to back of the mounting point on ECU. Small hole on back of the ECU up to cab.

You can try ANY KIND OF HOT WIRING, but nobody will notice the ECU is isolated from ground.

With Rev-N-Nator maybe easier without need to isolate, since they get the ground wired from back anyway

PurpleBeeper · Jan 30, 2017

68gtxman said:
Except that circuit may carry more current than the switch is rated for and could cause a meltd switch or non-start condition.

Good point... better be a high-amp switch

Bb70charger500 · Jan 30, 2017

A 45 works good for anti theft I rarely leave my car in attended if I do my club members are usually very close by .
I like the washer cut out idea I may us that myself

Hemirunner · Jan 30, 2017

GPS transponder is another option as well. Works well for the 'hook and run' or if your entire truck/trailer/car ensemble gets taken.

747mopar · Jan 30, 2017

Dennis H said:
Up your insurance, and park as smart as possible. Use a car cover. No way to prevent theft. Tow trucks trump all.

True but most thieves are too lazy to go to that extent lol. I think throwing the typical thief a curveball is enough to stop the theft from happening.

R/T · Jan 30, 2017

To prevent carjacking in the event that a shootout is not possible, i wired my electric fuel pump tru an extra foot dimmer, therefore as the thug is pulling me out me out i tap on the xtra hi/lo dimmer de-energizing the pump , all thats left to do after the thug drives off is to walk in the general direction and you will find your ride abandoned in the middle of the road with the door left open, just hop in , click on and drive off!

71GTX440 · Jan 31, 2017

PurpleBeeper said:
Another way to do basically the same thing is to splice in an on/off switch into the blue ignition wire. You can crank it, it will "try" to start, but won't run.

Are you referring to the dark blue wire coming from ignition switch, running through the bulk head connector on pin 23 and continuing on to the wire junction at the ignition resistor?

SlinktRR · Feb 1, 2017

Ive used the neutral safety switch to disable the ignition, no ground no start. But I'm always worried about a theft tow more than a drive away.

Doug Larsson · Feb 4, 2017

My relay say's on the back it's a 30/40 amp I think my switch is a 15 or 20 amp do I need to get a higher amperage switch ?

Installing a theft relay.

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