"No Cut" method for bypassing factory alarm

[1986911]

Last week I posted a question about arming and disarming the factory alarm in conjunction with an aftermarket system. I came to the realization that there are 2 resistors inside the key switch. One resistor is for on and one for off below are the measurements. I did not want to go this route

I decided to use the factory alarm plug in my install. It was actually pretty straight forward. The hardest part was getting the ventilation system out. On my 86 targa first you unplug the factory alarm harness then you need to connect some male spade plugs. The 2 #61 terminals to each other then connect the #87a to #15. Thats it!


I have the extra wires (red and blue instead of another yellow) because I wired my starter kill there. The 87a wire needs to see 12 volts in order for the engine to run. The #15 wire is hot when the ignition is open and does not shut off during engine cranking. Below is the wiring for the relay

On the relay you wire 86 and 87a to the #15 pin on the harness then 30 to the
87a pin on the harness. 85 goes to the negative output from the alarm or a manual toggle switch that goes to ground. I feel this is the best setup because if I have a complete alarm failure the car will still run. The only point which the relay actually interrupts current is when someone opens the ignition when the system is armed.
I hope this helps someone that hates cutting factory wires as much as I do.

[DRACO A5OG]

Nice Job 86!

Do you have the pic of the relay attached?

Also which output did you use from the After Market Alarm?

[Charlie V]

Agree with jumping #61 with #61.

Jumping #15 with 87A does not work on an SC. My alternator would not charge the battery with this jumper in place. Once removed, everything was fine.

[JMH82SC]

1986911, it's a small world as I'm in Tampa area with a White 82SC and also have a 74 MGB
Jon