[soule64]

I ran into similar problems rewiring my '76. One thing you have to remember is that the wiper system uses a series of grounds to switch the motor on/off/fast. The only hot wires that run thru the switch is for the backlight and washer clutch. Also, switches for 76-77 are different internally than 78+ and are NOT compatible (you can only function off, park and fast OR slow). I found a new OEM switch on Ebay (advirtised as one 75-76, but actually for 78+) for $12 and installed it because the original one on the truck had the backlight housing broken. I could not get both the fast/slow to work no matter what combination of wires I used. I thought the motor might be bad, so I replaced it for one for 1976, but acted the same. I finally bought another new motor, this time for a '78, and it works perfect. Switches for 75-76 are not compatible with 78+ motors and vice-versa. The only wire that I have that comes in close contact with the with the guage cluster is the hot wire for the switch's backlight (gray) that taps the instrumant backlights (also gray). I spent three days with one of our mechanical engineers trying to figure it out - I have a picture of the white board we used develop a schematic, but I can't seem to find it on this computer. If I find it, I'll post it.. The switch does not ground thru the mounting screws (on mine, anyway).