Anyone know what these are for? (switch and lights in dash bezel)
 

http://www.mydixiesys.com/72_GMC_LWB/P1010028.JPG
http://www.mydixiesys.com/72_GMC_LWB/P1010029.JPG

Does anyone have any idea what the toggle switch and red and green lights in the dash "might" be for? 1972 GMC 402BB with a 700R4 transmission. Looking at other dash bezels I'm pretty sure these aren't a stock item since they're nowhere to be found on replacement bezels.

When I crank the truck the red light comes on and stays on typically for quite a while, after a while the red light will go off and the green light will come on, pretty much only when I touch the gas (and I mean even lightly touch) and then again, a minute later I might touch the gas and neither light comes on.

I flipped the switch and nothing discernible happened, haven't flipped it going down the road for this unfounded fear that it'll "do something bad" (ahaha god what a chicken).

No telling without tracing the wiring. Have you tried that?

It's not stock, so it could be whatever project a long past PO was into. My guess is fuel tank select. Red light= portside tank, green light =starboard fuel cell. Hell, who knows? With out looking under the truck for extra fuel plumbing, it could be anything. If it's still lighting up, then it's connected to power, but if it's not doing anything, maybe you should delete it before it causes some other shorts. Did the guy who sold you the truck say anything about it?

Theory # 2
 

Then again, it may have something to do with your TH700R4. A tranny we don't see much in our '67/'72 world. The toggle may be the Overdrive select and the red or green LEDs may be OD status indicators. For example: Red = OD off, Green = OD engaged. Or vice versa?

My vote is theory #2. When you install an overdrive trans with a lockup converter in a vehicle with no computer, you have to install some way to operate it.

Could it be that they are connected to the choke/Temp settings, so that at first start up the red light is on as you stated and once it is warmed up to a set temp then the red light goes out and the green light comes on letting you it is warmed up and ready to drive? By reading your post that is the first thought I got.
Not sure though.

I was going with The Choke for $100.00 Bob!

The switch could be anything!
:eek:

When all else fails, trace the wires...

I'm guessing it controls the lock up converter power. I seem to recall reading something about a retrofit of a 700R4 with a setup like this that permitted the driver to control the lockup so it was not automatic.

I also wonder about an electric fan control. Does the truck have an electric fan? If so it might be an override switch and the lights might indicate if the fan is running or not.

I was wondering after reading about the 700r4 if maybe the switch wasn't simply an overdrive on/off selector, like on my wife's 03 minivan you can push a button on the gear switch and it turns off overdrive.

The lights I'm figuring have something to do with warming up since it's always red when cranked and turns green later on, but it doesn't seem to turn green until much later on long after when the motor is already reading around 160 on the temp gauge and everything seems like it should be toasty warm.

I'm going to take it in to a mechanic within a few days for a complete "physical" since I'm obviously no mechanic I want someone who is to go over it with a magnifying glass and fine tooth comb and give me a good idea of the full status of the mechanicals. The brakes have me a little concerned they don't seem to lock down as hard as I'd expect a power brake from so early to do. Show and go don't mean squat if you ain't got stop :D I'll ask the old owners just haven't gotten around to calling him. Was just wondering if this might be some kinda "semi popular" thing people did to these trucks.

OK the toggle switch is overdrive on/off, if I flip it up it doesn't go past the third gear and doesn't go into overdrive, if I shift it down it uses all the gears. I switched it up while driving today and after a second or so it'd shift out of 4th even if I were coasting so that's for sure what it is.

The lights I'm still not positive about.

Getting better gas mileage this tank, I've kept my foot outta it... Got about 7 or 8 on the first half tank I ran through it, took 12 gallons to fill it up and I'd put maybe 85 - 90 miles on it, already 70 miles into this tank and barely at 3/4 tank.