Anyone know what these are for? (switch and lights in dash bezel) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Gary · 02-17-2004, 07:46 AM

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).

krue · 02-17-2004, 07:56 AM

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

**'68OrangeSunshine** · 02-17-2004, 08:19 AM

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?

**'68OrangeSunshine** · 02-17-2004, 08:26 AM

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?

MrGoodpliers · 02-17-2004, 10:20 AM

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.

TsgtE662 · 02-17-2004, 11:05 AM

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.

67chevemall · 02-17-2004, 11:38 AM

I was going with The Choke for $100.00 Bob!

The switch could be anything!

twobrats71 · 02-17-2004, 12:32 PM

When all else fails, trace the wires...

oldsub86 · 02-17-2004, 01:40 PM

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.

Gary · 02-17-2004, 03:23 PM

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

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.

Gary · 02-18-2004, 05:47 AM

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.

02-17-2004, 07:46 AM	#1
Gary Senior Member Join Date: Jan 2004 Location: Harvest, AL Posts: 545	Anyone know what these are for? (switch and lights in dash bezel) 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). __________________ Gary Harris 85 Silverado - 87 Grand National 2007 Ardmore Car Show

02-17-2004, 08:26 AM	#4
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,284	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?

02-17-2004, 10:20 AM	#5
MrGoodpliers Registered User Join Date: May 2002 Location: Gainesville, Georgia Posts: 704	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. __________________ We made Oklahoma a little after 3, Randy & his brother Bob & my old GMC...

02-17-2004, 11:05 AM	#6
TsgtE662 2A674 Tank Rat Join Date: Jul 2003 Location: Maryland Heights, Mo. Posts: 626	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. __________________ '92 GMC Sierra, Sportside, 2wd, 350, Black '92 Chevy Silverado Extended Cab 4 x 4, Blue USAFR = 2A674 = Aircraft Fuel Systems Maintenance i.e. Tank Rat

02-17-2004, 11:38 AM	#7
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	I was going with The Choke for $100.00 Bob! The switch could be anything! __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

02-17-2004, 07:56 AM	#2
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,450	No telling without tracing the wiring. Have you tried that? __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

02-17-2004, 08:19 AM	#3
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,284	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?

02-17-2004, 12:32 PM	#8
twobrats71 Registered User Join Date: Dec 2003 Location: Rusk, Texas Posts: 37	When all else fails, trace the wires... __________________ Bryan http://community.webshots.com/user/twobrats71 1971 C-10 Short/Wide (see pics in link) Lexus Absolutely Red Air Ride American Racing Torque Thrust II's (17x8 front/17x11 rear) Chevy 350, Street & Performance Ram Jet 700R4 Transmission, 3.73 gears 4 wheel disc brakes 2 1/2" exhaust with dual Flowmasters Vintage Air Gaylord Cover Wife's Ride: 2002 Pewter Camaro SS (see pics at link)

02-17-2004, 01:40 PM	#9
oldsub86 Registered User Join Date: Dec 2002 Location: Canada Posts: 695	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. __________________ 1968 Chevy - 292 with a powerglide

02-17-2004, 03:23 PM	#10
Gary Senior Member Join Date: Jan 2004 Location: Harvest, AL Posts: 545	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 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. __________________ Gary Harris 85 Silverado - 87 Grand National 2007 Ardmore Car Show

02-18-2004, 05:47 AM	#11
Gary Senior Member Join Date: Jan 2004 Location: Harvest, AL Posts: 545	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. __________________ Gary Harris 85 Silverado - 87 Grand National 2007 Ardmore Car Show



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