Tandem Lock Light - The 1947 - Present Chevrolet & GMC Truck Message Board Network

'69C-10 · 03-29-2018, 02:17 PM

So my '71 C10 has a heavy truck cluster in it with the Tandem Lock Light. Yesterday that light came on and has remained on since. Out of curiosity any ideas as to what would be causing that light to come on?

**leddzepp** · 03-29-2018, 02:19 PM

Stomp on your brake pedal really hard. The light will go out.

**jocko** · 03-29-2018, 10:58 PM

Scott I thought that was how to re-center the shuttle valve (to extinguish the brake light that had tripped) once the leak that caused the pressure differential between front and rear systems had been repaired? I thought the tandem lock light had no purpose when a medium duty cluster was installed in a light duty truck?

'69C-10 · 03-29-2018, 11:02 PM

As far as I know there is no purpose for that light in a light duty truck. Just curious as to what would activate it all of the sudden. I'll dig a bit tomorrow.

**leddzepp** · 03-29-2018, 11:05 PM

He has a heavy cluster in a c10...it IS the brake light that is coming on

. The tandem lock is in the same spot in a heavy cluster that the brake light is in the 1/2 ton cluster.

C10 - C90 Bill · 03-29-2018, 11:09 PM

Check to see if all of a sudden your truck now has an extra axle on the back end of it.

Seriously though, I never knew our smaller trucks used the same lenses that the big trucks have, unless it was just some kind of fluke. But what may really has happened is that someone might have install a dash cluster from a big truck. I would love to see a picture of that.

Edit: leddzepp, looks like we were both responding at the same time.

'69C-10 · 03-29-2018, 11:13 PM

Quote:

Originally Posted by leddzepp

The tandem lock is in the same spot in a heavy cluster that the brake light is in the 1/2 ton cluster.

Ahhhhh, touché.

'69C-10 · 03-29-2018, 11:16 PM

Quote:

Originally Posted by C10 - C90 Bill

Seriously though, I never knew our smaller trucks used the same lenses that the big trucks have, unless it was just some kind of fluke. But what may really has happened is that someone might have install a dash cluster from a big truck. I would love to see a picture of that.

The cluster is out of a medium duty truck as it has the tandem lock light and an overspeed light. Without these illuminated it looks just like any other light duty cluster. I didn't realize it was a medium duty cluster until I pulled it and was replacing bulbs.

I don't have a good picture of it now, but can post one in the AM.

'69C-10 · 03-30-2018, 09:33 AM

Of course after being on for 3 days straight, the light is out this am. If you look close at the 7-8 o'clock range of the fuel gauge you can faintly see where the light is located.

C10 - C90 Bill · 03-30-2018, 10:11 AM

Thanks for the picture. I'll have to check on my Cluster. I took one out of a 2-Ton for the Vacuum Gauge.

I like the Tach by the way.

davepl · 03-30-2018, 11:09 AM

I'm searching for an Air Pressure gauge (not vacuum, but air system pressure) if anyone sees or has one in these clusters!

C10 - C90 Bill · 03-30-2018, 11:54 AM

That's what I was looking for myself, an Air Pressure Gauge in some local junk yards, but decided to grab the Vacuum Gauge while I was at it.

'69C-10 · 03-30-2018, 06:05 PM

Quote:

Originally Posted by C10 - C90 Bill

Thanks for the picture. I'll have to check on my Cluster. I took one out of a 2-Ton for the Vacuum Gauge.

I like the Tach by the way.

No problem and thanks!

03-29-2018, 02:17 PM	#1
'69C-10 Registered User Join Date: Nov 2012 Location: Freeport, IL Posts: 73	Tandem Lock Light So my '71 C10 has a heavy truck cluster in it with the Tandem Lock Light. Yesterday that light came on and has remained on since. Out of curiosity any ideas as to what would be causing that light to come on? __________________ '67 C-10 SWB '18 Sierra Denali '18 Volvo XC90

03-29-2018, 02:19 PM	#2
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 19,981	Re: Tandem Lock Light Stomp on your brake pedal really hard. The light will go out. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man

03-29-2018, 10:58 PM	#3
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,934	Re: Tandem Lock Light Scott I thought that was how to re-center the shuttle valve (to extinguish the brake light that had tripped) once the leak that caused the pressure differential between front and rear systems had been repaired? I thought the tandem lock light had no purpose when a medium duty cluster was installed in a light duty truck?

03-29-2018, 11:02 PM	#4
'69C-10 Registered User Join Date: Nov 2012 Location: Freeport, IL Posts: 73	Re: Tandem Lock Light As far as I know there is no purpose for that light in a light duty truck. Just curious as to what would activate it all of the sudden. I'll dig a bit tomorrow. __________________ '67 C-10 SWB '18 Sierra Denali '18 Volvo XC90

03-29-2018, 11:05 PM	#5
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 19,981	Re: Tandem Lock Light He has a heavy cluster in a c10...it IS the brake light that is coming on . The tandem lock is in the same spot in a heavy cluster that the brake light is in the 1/2 ton cluster. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man

03-29-2018, 11:09 PM	#6
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,064	Re: Tandem Lock Light Check to see if all of a sudden your truck now has an extra axle on the back end of it. Seriously though, I never knew our smaller trucks used the same lenses that the big trucks have, unless it was just some kind of fluke. But what may really has happened is that someone might have install a dash cluster from a big truck. I would love to see a picture of that. Edit: leddzepp, looks like we were both responding at the same time. __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

03-30-2018, 09:33 AM	#9
'69C-10 Registered User Join Date: Nov 2012 Location: Freeport, IL Posts: 73	Re: Tandem Lock Light Of course after being on for 3 days straight, the light is out this am. If you look close at the 7-8 o'clock range of the fuel gauge you can faintly see where the light is located. __________________ '67 C-10 SWB '18 Sierra Denali '18 Volvo XC90

03-30-2018, 10:11 AM	#10
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,064	Re: Tandem Lock Light Thanks for the picture. I'll have to check on my Cluster. I took one out of a 2-Ton for the Vacuum Gauge. I like the Tach by the way. __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

03-30-2018, 11:09 AM	#11
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Tandem Lock Light I'm searching for an Air Pressure gauge (not vacuum, but air system pressure) if anyone sees or has one in these clusters! __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

03-30-2018, 11:54 AM	#12
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,064	Re: Tandem Lock Light That's what I was looking for myself, an Air Pressure Gauge in some local junk yards, but decided to grab the Vacuum Gauge while I was at it. __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan Last edited by C10 - C90 Bill; 03-30-2018 at 02:02 PM.



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