After spending some time searching I thought adding cruise control to my 1993 Impreza ATX FWD would be easy. Pulled the dash switch, cruise control computer, steering wheel mounted control, the vacuum port, and the underhood cruise control module from a 1993 Impreza ATX AWD at the junkyard and installed them into my car which was prewired. After doing that work it doesn't even try to work at all. The cruise button doesn't light up and I tried messing with the controls while driving and they did nothing. I know on my Forester and Legacy there was a relay that would click when you'd press the cruise button but I don't hear it on this car. Did I miss a relay somewhere that I need to add?

 

I just realized I didn't add the brake switch but I don't think that would cause the system to not even power on at all...

If you didn't add the brake switch, I'd start there since that's something you know you need. It would not surprise me if the system did not work without the brake switch - that's a safety device. Hitting the brakes without turning of the cruise control sounds like bad mojo!!!!!

Right, I can imagine that being the reason it wouldn't set a speed, but the light on the dash switch or the power relay for the cruise didn't turn on or off either.

Gotcha, be nice to have an FSM schematic, did you get that? That would narrow down all the critical parts. Like you said, probably one small relay or something out there.

 

You hooked up the throttle cable and everything?

 

I know folks that have done this and said it's straight forward, so you're just missing something.

I wish I had an FSM for the car but I unfortunately do not have one. It was wierd as everything was plug and play, there's a fuse in the spot it needs to be, and I didn't find anything else out of line sans the brake switch. All the information I can find pertains to newer Impreza's unfortunately. I have the oddball 1993...

This is for the 1997 cruise add on, but may help

 

http://main.experiencetherave.com/subaru_manual_scans/FSM_Scans/1997_Impreza_Cruise_add-on.pdf

As seen on the diagram, the extra set of contacts in the brake pedal switch is normally closed. If it's open, it may well be that the system won't power up.

Thanks for the diagram! I'll try jumping the connector to test it until I can get to the junkyard again. If it works I'll swap the brake switch, if it doesn't... well... who knows what's up then.

Yes you need the correct brake switch and clutch switch if you wire it up that way, if you have a 5sp trans.

Just for fun I tried jumping that brake switch... and was rewarded with failure. I wonder if the cruise switch on the dash is bad. Is it supposed to click on and off or is it just a momentary switch?

 

If an older Legacy has the same plug type I'll try grabbing one of those (and the proper brake switch as well) and see if that fixes it.