Today I sat down and figured out how to wire the stock control stalk to my aftermarket cruise control (a Rostra GlobalCruise electric cruise control).
From my research it seems that most (if not all) aftermarket cruises nowadays use the same two control stalk wiring setups; one that is open-circuit (or "normally open") and one that is closed-circuit ("normally closed"). Both types are supported by the Rostra unit, and I think this will be the case for most other aftermarket cruises as well.
wolf_walker wired his stock controls up as closed-circuit controls, which have a complex and ugly setup and required him to use a relay and a diode to get it working. If it's possible, wiring the stock controls up as open-circuit ones instead is a simple 5 minute job requiring no extra parts
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The stock controls in the 123 has a 5 pin connector. Here's what each is for, and the color of the wire associated with it:
1: Gray wire, always +12 except when controls are in "off" position
2: Red/yellow wire, +12 power
3: Yellow/green wire, +12 when controls are in "decel" position, neutral otherwise
4: Green/red wire, +12 when controls are in "accel" position, neutral otherwise
5: Blue/red wire, +12 when controls are in "resume" position, neutral otherwise
The open-circuit aftermarket cruise control setup wants this (wire colors should be standard but no guarantees!):
Brown wire: always +12 except when controls are in "off" position
Red wire: +12 power
Yellow wire: +12 when controls are in "resume/accel" position, neutral otherwise
Green wire: +12 when controls are in "set/coast" position, neutral otherwise
Wiring for power is obvious (red/yellow wire on stock controls to red wire on aftermarket cruise).
Wiring for the off switch is also obvious (gray wire on stock controls to brown wire on aftermarket cruise).
After that, wiring is somewhat a matter of personal preference. The stock controls have 3 switches besides "off": accel/set, decel/set, and resume. None of these coincides perfectly with the 2 the aftermarket cruise wants: resume/accel and set/coast. Take your pick of two the remaining three positions and connect the appropriate wires, or jumper two of the stock wires together so that two of the positions perform the same function. My personal preference:
On the stock controls, "accel/set" is now "resume/accel" because it makes sense to me to push up to accelerate, and tapping up once for resume will be easy to remember. (Green/red wire on stock controls to yellow wire on aftermarket cruise).
On the stock controls, both "resume" and "decel/set" are now "set/coast". This way decel/set still functions as would be expected, but I can also turn on/set the cruise control by pulling towards myself rather than pushing down (pushing "decel" to set the cruise control seems counterintuitive to me). (Both Blue/red and yellow/green wires on stock controls to green wire on aftermarket cruise).
Good luck to everyone else trying this mod! It's totally worth it - a functional, smoothly-operating cruise control *with a 3 year warranty* for much less than the cost of buying a new cruise amp that will probably crap out a year later...