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I am look to install a simple anti-theft toggle switch that is inline with one of the DME relay wires that goes to the fuse box.
The following is a DME relay pin diagram
dme-relay-diagram-1.gif (7.91 KiB) Viewed 1890 times
Brief research has told me that I should be installing it on either line 85b or 85 - but I have not found a conclusive answer.
Does anyone know which one I should wire it to?
I also intend to use this switch to give the car a few cranks and build oil pressure after long intervals of sitting to avoid dry starts.
My first thought would be to cut power to the fuel pump. Those wires are easy to access (or its fuse) and that would accomplish your goal I'd think. I would not try to interrupt ground to the DME. If the dedicated grounds are cut, the current might still find alternate routes to the chassis ground through DME components and engine sensors that are not capable of carrying the current (i.e., you might fry something).
Tom wrote: Sun Sep 11, 2022 9:12 am
My first thought would be to cut power to the fuel pump. Those wires are easy to access (or its fuse) and that would accomplish your goal I'd think. I would not try to interrupt ground to the DME. If the dedicated grounds are cut, the current might still find alternate routes to the chassis ground through DME components and engine sensors that are not capable of carrying the current (i.e., you might fry something).
That does seem like a possible concern. After more consideration, I may follow your advice and maybe splice into the fuel pump fuse. It looks to be a 15 amp fuse (34 on late car fuse boxes). In that case I will have to be sure to use a quality switch, perhaps aircraft style with the flap.
Another area where a kill switch could be wired in is at the orange Airbag Controller located above and forward of the glovebox if your car is airbag equipped. The controller sends a signal to the DME relay and if that signal is interrupted the car won't start. You could splice in a switch to either the Black/White wire which provides power to the Controller, or the Black/Red wire which supplies power back to the DME relay. The wire colors are those on the car harness side of the 7-Pin connector. The switch could also be spliced in on the controller side of the connector as there may be more wire to work with, but I don't recall the wire colors.
When I disabled the airbags in my S2 to install a 968 CS steering wheel I used a version of this to disable the airbag warning light. I cut off the connector from a junk controller and jumped the wires on the controller harness that corresponded to the Black/White and Black/Red, thus assuring the DME relay always gets power. In retrospect I could have wired in a kill-switch at that time.
Posting some updates.
I took everyone's consideration and decided just to open the fuse box up first and scratch my head afterwards.
In the end, I ended up going with the solution outlined in this video:
The video was for an S2, but my late 86 NA had the same wire (yellow/black).
The following is the yellow/black wire, I had cut to check how many pixies go through it. I guess it was obvious by the gauge of the wire, but not much current. Seems like a good candidate for a kill switch?
PXL_20220914_204545223.jpg (1.49 MiB) Viewed 1722 times
PXL_20220914_212353824.jpg (510.11 KiB) Viewed 1722 times
With the fuse box installed, the wires are easily accessed through the driver footwell
PXL_20220914_212457822.jpg (1.52 MiB) Viewed 1722 times
Temporarily hooked up a switch, but will be thinking an a creative spot to hide it in the future.
PXL_20220914_215505050.jpg (621.78 KiB) Viewed 1722 times
This solution worked well. Tbh I still don't know exactly what the purpose of the yellow/black wire is. With the toggle switch in the off position the car will crank but not start. Flip it on, and the car cranks and starts right up as usual.
Great update, thanks. For what it's worth, that's the exact wire that was cut on my car when Circuit City installed an alarm back in the late '80s. Took me forever to figure out how they wired it in when it stopped working. I didn't have the nerve to pull up the fuse box though, so had to solder the wires back together laying on my back with the seat removed. Good times...
