As my hyperkilometring evolves, I've found I use my kill switch more and more. When using it while rolling, I've usually restarted by letting out the clutch, but it's very hard to do this smoothly, since of course I can't match engine RPM to gearbox RPM when the engine isn't running yet. I think if you do this smoothly, it's hard on the clutch, and if you do it roughly, it's hard on the engine, transmission, and mounts. Thus, I've changed to restarting using the key.
The problem is, this is kind of awkward when in motion, so I came up with the idea of installing a "revive switch". It basically duplicates the process that turning the key to START does, but with just a button next to the kill switch. Here's the schematic of what I've done, added to a stretched diagram from the service manual:
There are two identical SPDT relays, with their coils wired in parallel, and powered by the RUN-only wire from the ignition switch. A pushbutton to ground is used to energize the relays. [Aside: The diodes are part of the relays. My kill switch relay didn't have one, and always produced a loud pop in the sound system when the button was released. Adding a diode completely eliminated that, so I ordered relays with diodes already installed this time.]
When the really is
not energized, the RUN-only wire (orange) goes through the normally-closed contacts of the first relay, and from there on to the RUN-only section of the fuse box. Likewise, the RUN/ACC wire (brown) goes through the normally-closed contacts of the second relay, and then on to the fuse box. Both of these wires were previously connected directly to the fuse box.
When the "revive" button is pushed and the relay
is energized, the power from the RUN-only wire is redirected to the starter circuit instead, and the RUN-only part of the fuse box no longer gets power (as it shouldn't during starting). Likewise, the RUN/ACC part also no longer gets power (as it also shouldn't).
As far as the rest of the car's electrical system sees things, exactly the same thing has just happened as if I'd turned the key from RUN to START.
Here's how it looks under the dash. I fashioned a small mounting plate for the relays out of 1/8" aircraft plywood, and bolted it to a metal rail close to the wiring harness:
Here you can see the two buttons. The yellow one was formerly my kill switch, but is now the revive switch. The more aptly coloured red one is the kill switch now:
I did run into one snag... The schematic I had, from what appears to be a scanned version of the service manual, had the brown and pink wires from the the ignition switch swapped. So pressing the button disconnected stuff that was supposed to remain powered during START (like the BCM), and did not disconnect stuff that should have been (like the audio system). The engine cranked, but wouldn't start.
At first I thought I'd run afoul of the PassKey II security system, but after much Googling and pondering the symptoms, I came to the conclusion that this wasn't the case. I went back and monitored the voltage on each wire out of the switch in each switch position and discovered the error in the wiring diagram. After some more Googling, I found another diagram on SaturnFans.com (in black and white, but with the colours labelled), that had them indicated correctly. After rewiring, everything worked. Unfortunately I now have an unnecessary splice in the pink wire.