Fix for ECU 1&2, among other things, 12V controller
 

Greetings, During my search for lightweight alternatives and upgrading old technology I discovered how CPUs 1 & 2 in the FD control things like the turn signals, hazard lights, and 15 min rear defog timer. So I searched for how to replace those with modern tech while minimizing the need for weird relays and flasher modules. Behold the Programmable Logic Controller (PLC). It is essentially a small computer with transistors and relays that can be programmed as the user sees fit. The one I purchased is the TECO SG2-20HR-12D, This runs on 12V, has 12 inputs and 8 outputs, and is expandable with smaller modules if needed. The outputs can handle up to 8 Amps each.

The software is free and a cable is needed to connect a PC to the PLC or else you will need to program by hand using 4 arrow buttons which can be tedious, or you can by a more minimal version of the PLC as well as the controller module which has a better display and more buttons for programming and logging.

So here are some of the things it can do
Standard IF/THEN commands - IF a signal comes to input X, open the relay for output Y as long as X receives signal (normal relay)
Timers - If a momentary signal comes to X, open output Y for so many minutes/seconds/milliseconds (defog timer) getting the momentary signal again resets the timer; if a signal comes to X, open output Y for so much time, then close it and repeat (flasher), if a signal comes to X, flash outputs Y and Z (hazards).

The outputs can run PWM as well, there are counters, timers, and all kinds of stuff using logic functions like OR, AND, NOR, NAND. I'm sure someone with more electrical knowledge could figure out how to have a temp or pressure sensor drive a relay as well with it.
I believe it could even be used to run a push button start for the car, essentially limited by Amperage and your own creativity

This particular PLC has built in memory and doesn't require a constant 12V to retain its memory, so it will turn on when you turn the car on and be ready to go and operate everything you need it to. It is smaller than the Joint Box as is but with expansion modules it will be bigger.

The software is pretty easy to use, it can be programmed with HEX or ladder logic, I found ladder logic fairly simple to get a grasp of and figured out the timer for defog, flasher for both turn signals, and hazard flasher using 4 inputs and 3 outputs, and now am wondering what else I could use it for, windshield wipers but that's already fine in the combination switch.

SG2 PLC

This PLC I believe is around $89 at factorymation.com, not bad considering what it does and how pricey and scarce CPU2 can be, as well as dealing with leaky capacitors and stuff

nice find.... so you actually have this working in your car now?

It's been bench tested so far with a spare 12v battery and wired up bulbs and the defogger relay. Being that it has to be under 8A per internal relay it cant drive major systems directly save for LEDs.

You can also pick exactly how long you want the flashers to flash, normally its .5s on .5s off, but you could do faster or slower and even alternate your hazards if you wanted to.