What is this light? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CG · 07-06-2008, 09:41 PM

I bought this rebuilt gauge cluster from a board member ages ago and never used it. I put it in my k20 a few months back. Today for the first time I noticed this light flashes on for a second as I start the truck up...not very attentive am I? Im guessing he got this gauge off a larger size truck...Curious what a tandem lock is.

t&tkennels · 07-06-2008, 10:21 PM

On a tandem axle truck , only one axle pulls in normal mode like for highway use. But when us but when using off road like in a slick or muddy situation you can lock both axles in so they both pull. Its usaully found on dump trucks or road tractors & activate by air , on older trucks maybe they were electric or work by some kind of linkage.

**Boog** · 07-06-2008, 10:24 PM

It sounds like a power divider for a tandem axle truck. Locks in both axles to pull in slippery conditions.

mvfd70 · 07-06-2008, 10:24 PM

Usually on a larger truck with tandem axles (two rear axles) only the more forward of the rear axles has power to it. If you look at the Diff. housing on that axle it has an output shaft and then a short drive shaft going to the most rear axle. When the "Tandem Lock" is engaged, power is given to both rear axles making both of them drive axles. It aids in getting traction since 8 tires spin instead of 4.

stllookn · 07-06-2008, 10:27 PM

How cool is that? I love it!

ChevLoRay · 07-06-2008, 10:28 PM

So, it's a guage cluster from a big truck, probably at least a C-60.

I drove a '74 C-65 tri-axle dump that had locking twin screw differentials. When the going got rough, as t and t said, you could lock the diffs and all eight rear tires would pull together. It was only for straight pulling, with no differential action in turns. If you needed it, you were lucky to have it.

I broke the yoke on the front twin screw, while loaded with nearly 20 tons of hot mix asphalt....on a hill. Ever hear of "fail-safe brakes"? With air brakes, the LACK of air pressure is what makes them work. When you are rolling backwards, with a curve at the bottom of the hill and you have no engine and no air and no brakes......let's just say, "Life is good!"

The asphalt that I had in the bed that day? It's still in the ravine where I dumped it. That was in '75....July 2, to be exact.

CG · 07-07-2008, 12:08 AM

Thanks for the info guys. I can pretend Im driving a bigger rig. Wonder if Ill have to get my CDL now? =)

**special-K** · 07-07-2008, 05:59 AM

Maybe you won`t get stuck when the light comes on.

Longhorn Man · 07-07-2008, 10:44 PM

since no one mentioned it, that is the brake warning bulb, with the wrong lens due to the fuel guage being out of a c/40 or bigger.

**special-K** · 07-08-2008, 12:01 AM

Maybe you won`t stop when the light comes on.

CG · 07-08-2008, 12:58 AM

Could there be any particular problems running this large truck gauge panel on my truck? I had an original tach dash in it before I put this one in. Everything on it worked perfectly...it was just kind of old looking so I put this one in that I bought for a project I let go. The speedometer doesnt work correctly, the odometer barely works, the temp gauge pegged as soon as I started the truck first time after I installed it. The tach works, but sometimes reads way higher than it should be (Sometimes at 60mph it will almost be pegged, sometimes its normal). I haven't hooked up the oil or vac gauge yet. Do you think any of the weirdness is because of the style truck it came off of? Doesnt seem like it would make a difference to me.

The problem is I purchased it at least a couple of years ago and it had just been sitting in the top of my closet, so any kind of warranty the builder may have given would be way passed...and the other part of the problem is...I dont remember who I purchased it from...Crazy I know.

Longhorn Man · 07-08-2008, 06:15 AM

the only things you'll notice, is the wrong lens on the light, and the oilpressure guage is a n 80 ppound guage instead of a 60 pound guage... so you'll be at mid guage @ 40 PSI instead of 3.4-ish guage @ 40 PSI... the guage will look like the oil pressure is lower than it is.
Those are the only things you'll notice, and quite possibly, all that there is at all. (been a while since I messed with the big truck guages)

**special-K** · 07-08-2008, 07:04 AM

Maybe there`s a short in the printed circuit?I know the temp gauge pegs when it`s grounded out and with the warning like lighting makes me suspect something.

Longhorn Man · 07-08-2008, 04:00 PM

it's supposed to come on when the key is in the crank position.

07-06-2008, 09:41 PM	#1
CG BlahBlahBlah Join Date: Feb 2002 Location: Wa. Posts: 19,833	What is this light? I bought this rebuilt gauge cluster from a board member ages ago and never used it. I put it in my k20 a few months back. Today for the first time I noticed this light flashes on for a second as I start the truck up...not very attentive am I? Im guessing he got this gauge off a larger size truck...Curious what a tandem lock is. Attached Images

07-06-2008, 10:21 PM	#2
t&tkennels Registered User Join Date: Sep 2007 Location: creedmoor n.c. Posts: 188	Re: What is this light? On a tandem axle truck , only one axle pulls in normal mode like for highway use. But when us but when using off road like in a slick or muddy situation you can lock both axles in so they both pull. Its usaully found on dump trucks or road tractors & activate by air , on older trucks maybe they were electric or work by some kind of linkage.

07-06-2008, 10:24 PM	#3
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,118	Re: What is this light? It sounds like a power divider for a tandem axle truck. Locks in both axles to pull in slippery conditions. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

07-06-2008, 10:24 PM	#4
mvfd70 Registered User Join Date: Jan 2007 Location: Opdyke, IL Posts: 775	Re: What is this light? Usually on a larger truck with tandem axles (two rear axles) only the more forward of the rear axles has power to it. If you look at the Diff. housing on that axle it has an output shaft and then a short drive shaft going to the most rear axle. When the "Tandem Lock" is engaged, power is given to both rear axles making both of them drive axles. It aids in getting traction since 8 tires spin instead of 4. __________________ 1978 Chevrolet Silverado 3/4 ton 400 small block. 2000 F-250 Powerstroke 2002 GMC Yukon Denali XL

07-06-2008, 10:27 PM	#5
stllookn Saving 1 truck at a time! Join Date: Aug 2001 Location: Kent, WA Posts: 6,465	Re: What is this light? How cool is that? I love it! __________________ '68 C20 Longhorn 50th Anniversary 400/TH400 '68 C20 Longhorn 50th Anniversary 468/TH400w/buckets '72 C20 Halfhorn (Longhorn w/o cab and front clip) '69 Flxible Cruiser (look up ugly in the dictionary)

07-06-2008, 10:28 PM	#6
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: What is this light? So, it's a guage cluster from a big truck, probably at least a C-60. I drove a '74 C-65 tri-axle dump that had locking twin screw differentials. When the going got rough, as t and t said, you could lock the diffs and all eight rear tires would pull together. It was only for straight pulling, with no differential action in turns. If you needed it, you were lucky to have it. I broke the yoke on the front twin screw, while loaded with nearly 20 tons of hot mix asphalt....on a hill. Ever hear of "fail-safe brakes"? With air brakes, the LACK of air pressure is what makes them work. When you are rolling backwards, with a curve at the bottom of the hill and you have no engine and no air and no brakes......let's just say, "Life is good!" The asphalt that I had in the bed that day? It's still in the ravine where I dumped it. That was in '75....July 2, to be exact. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. Last edited by ChevLoRay; 07-06-2008 at 10:30 PM.

07-07-2008, 12:08 AM	#7
CG BlahBlahBlah Join Date: Feb 2002 Location: Wa. Posts: 19,833	Re: What is this light? Thanks for the info guys. I can pretend Im driving a bigger rig. Wonder if Ill have to get my CDL now? =)

07-07-2008, 05:59 AM	#8
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,861	Re: What is this light? Maybe you won`t get stuck when the light comes on. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

07-07-2008, 10:44 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: What is this light? since no one mentioned it, that is the brake warning bulb, with the wrong lens due to the fuel guage being out of a c/40 or bigger.

07-08-2008, 12:01 AM	#10
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,861	Re: What is this light? Maybe you won`t stop when the light comes on. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

07-08-2008, 12:58 AM	#11
CG BlahBlahBlah Join Date: Feb 2002 Location: Wa. Posts: 19,833	Re: What is this light? Could there be any particular problems running this large truck gauge panel on my truck? I had an original tach dash in it before I put this one in. Everything on it worked perfectly...it was just kind of old looking so I put this one in that I bought for a project I let go. The speedometer doesnt work correctly, the odometer barely works, the temp gauge pegged as soon as I started the truck first time after I installed it. The tach works, but sometimes reads way higher than it should be (Sometimes at 60mph it will almost be pegged, sometimes its normal). I haven't hooked up the oil or vac gauge yet. Do you think any of the weirdness is because of the style truck it came off of? Doesnt seem like it would make a difference to me. The problem is I purchased it at least a couple of years ago and it had just been sitting in the top of my closet, so any kind of warranty the builder may have given would be way passed...and the other part of the problem is...I dont remember who I purchased it from...Crazy I know.

07-08-2008, 06:15 AM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: What is this light? the only things you'll notice, is the wrong lens on the light, and the oilpressure guage is a n 80 ppound guage instead of a 60 pound guage... so you'll be at mid guage @ 40 PSI instead of 3.4-ish guage @ 40 PSI... the guage will look like the oil pressure is lower than it is. Those are the only things you'll notice, and quite possibly, all that there is at all. (been a while since I messed with the big truck guages)

07-08-2008, 07:04 AM	#13
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,861	Re: What is this light? Maybe there`s a short in the printed circuit?I know the temp gauge pegs when it`s grounded out and with the warning like lighting makes me suspect something. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

07-08-2008, 04:00 PM	#14
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: What is this light? it's supposed to come on when the key is in the crank position.



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