by saying "It works fine & dandy except for the lights" are you saying all of the controls and AC MAX button worked perfect? the reason I ask is because I tried that swap a few years back with NO success... I used a known good unit from a friends truck and when installed it did a light show and nothing worked, my friend thought I had burned up the unit but it worked fine when he put it back in his truck...
Yep, everything works like the old one did, even the "new" max A/C button. What year is your truck? We used to have an '88 and I tried the same swap with a different module and that didn't work. It did at first but then the vent position indicators started flashing and it stopped responding. Interesting to note that most of the wires for that '88 going into that module were white & thicker, like vacuum lines. Before I unplugged the wiring harness that's what I thought they were, like some hybrid unit. On this '89, none of the wires for the truck's harness are white, but none of them matched the wires for the '93 module so initially I didn't expect this swap to work either. Could be why the illumination lights don't work either, as I find it hard to believe all three bulbs are burned out. I won't know until I get the thing apart again & bench test it with that donor harness, man am I glad I take those.
Anyway, I think the trick to the swap is to do the ole Nintendo trick- as in clean the contacts really well with alcohol and also clean the pins of the harness the best you can. I then put dielectric schmoo in the harness before plugging it in to test. Then I flipped the key on, let the unit power up, moved the temp all the way to hot (as it was with the old one) then turned it to defrost and low blow speed. Heard electrical servo motors move. When they stopped, I cycled to floor. Then cycled the temp setting to max cold. Noticed display changed faster than old unit but no longer did the "hold 3 seconds and it'll automatically go full tilt heat/cold". From here I tried every other position too, no flaws or problems. My old '88 would have started flashing a light show by then. So I figured it was good, pondered about the illumination lights but mistakenly assumed that since everything else worked that those would too so put it all back together..
Also, while it may not matter I previously turned the old unit to "Off" and it was at the max heat setting before I removed it (with key off as well).
I am not sure why the swap worked in this '89 but not in our '88. Perhaps the module senses servo feedback or position of them and the older ones aren't compatible.. I did have to swap the blend door servo motor by the gas pedal on the '89 and it came from a newer truck too. Our '88 only had 66k miles on it and it sat for at least a good decade so perhaps things were too stiff for updated module's liking. Not sure..
Hmm, those look too wide.. The ones in it are narrower. Worst case scenario if all three bulbs are indeed burned out I'll try and swap the ones from my old unit over to this one. I'll bench test it first since I have a spare harness to test it with.