Replaced headlight switch on my S4 with a good one from a S5... small problem.
 

My parking and dash light portion of my old switch on my '87 GXL was burnt out, so the previous owner had connected one of the red/blk wires to the thicker red/grn wire and it actually worked.

Well, being one to do things properly, I cut that connection, then bought a switch off a gentleman in the for sale section and plugged it in (this switch was from a S5 coupe). The parking lights now work as they should, but the headlight retract action is reversed. When the switch is off, they are up, and when you click it to the full on position, they go down, but the headlights are on :sigh:.

I pulled both diagrams for the S5 and the S4 lighting circuit, but at first glance they appear almost identical, and I don't really see anything that would cause this.... I did try playing with the cleaning retract/extend switch, and that still didn't cause a correction.

Is there just something goofy in the system's logic and I should try some wierd install tips, or do I actually need a S4 switch?

wish i could help, but i have a whacky electrical problem too, after replacing my head light switch (with a used unit) my boost gauge would only light up when i turned on the rear defroster, if i turned on the head lights only, the boost gauge will not light up, only when i turn on the defroster then the boost gauge will light up.

I just pulled both apart, and at first glance, the PCB on the S5 switch does look different, but I haven't begun to test things out yet.

^ Your problem sounds like a bad switch as well, although it could be a short in teh harness maybe?

bad switch, and the boards are different, but the switches are interchangeable.

Ah, the master speaks. :D I pulled my de-bunked old switch apart, and the line for the parking light chunk is completely dead. I couldn't pull the complete switch out of there (but I can see the little copper things moving in there when I flip it around. I soaked that puppy in contact cleaner and I've been clicking it forward and back while watching my Star Trek TNG DVDs. :D

From what you've said though, can I just de-solder the newer switch's board off and swap the board from my S4 switch into the S5 switch "chassis"?

I just didn't try hard enough. I pulled it out of it's "bath" and pryed at it a bit more and it popped out. These switchs are a pain in the ass, you must really get some odd twisted enjoyment out of rebuilding them. I think my biggest problem has been my crappy Radio Shack solder sucker, it just doesn't get the job done.

Anyways, here's the culprit:

http://img125.exs.cx/img125/4743/img36237qp.jpg

Looks pretty nasty, but replacing it with the S5 switch assembly should be cake now that I know not to take the whole board out. :D

Sweet, good news. I didn't canabalize my S5 switch. I sanded the contacts on the S4 switch, wiped everything up with vasoline, lubed teh moving assemblies, and re-soldered everything.

I also ran some wires on some of the traces that didn't look too healthy. Put it in the car, and everything works great. :D

Expect a write-up in a bit.