73-87 Chevy _ GMC Trucks > Instrumentation

1985 C10 volt gauge question

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recoil:
Hello everyone.  I hope the group doesn't mind but I would love to get a second opinion before I buy a new volt gauge.

My volt gauge doesn't work.  I removed it and measured the cluster "middle top" and "right" clips with a multi-meter (as I'm facing the cluster).  I see 12v across them with ignition on only.  There is no clip on the left side (missing?) 

I connected a 9v battery to those same two contacts on the back of the gauge and nothing happens.  If I connect the 9v battery the the middle top post and the left post (as I'm looking at the back of the gauge), it goes to 18v (from a 9v battery?).

I'm thinking my gauge is broken. 

Just wanted a second opinion before throwing money at the problem.

Thanks!
Steve
Hampton, Virginia
LS 85 C10

bd:
Excerpt from Functional Tests of Factory GM Electric Gauges...

"For Truck Years:  1976 - 1987 (91)

The instrument cluster volt gauge is a direct sensing gauge electrically connected between 12-volt ignition and cab ground.  There is no external sender for the volt gauge.  Verify 12-volt ignition power, ground, and gauge connections to the flexible printed circuit using a handheld voltmeter and test light to determine the viability of the gauge and its circuitry.  Correct accordingly."


--- Quote from: recoil on September 19, 2022, 09:50:41 AM ---I'm thinking my gauge is broken. 

--- End quote ---

If you've verified power and ground to the voltmeter, then this ^^^^^.

recoil:
Are all three clips needed on the back?  I have 12v (up to 14 when the engine is on) across the two that are present.  But when I plug in my new gauge, it goes from <8 to about 9 (it moves but doesn't go to 14 when the engine is on).  The old gauge didn't move one bit so this is a step in the right direction but way off.

Thanks!
Steve

bd:
Only two gauge pins are used.  The spring clips in the image above appear spread open a bit too far.  The gauge may have poor connections.  You may need to bend the clips slightly to increase contact pressure with the gauge pins and the PCB.

With the cluster removed from the dash, push the clips out the back of the cluster housing.  Using a soft pencil eraser, gently burnish the copper foil under the clips until shiny.  Be very careful to avoid dislodging the foil from the plastic backing; it's an easy mistake to make.  Use a pair of needle nose pliers to slightly bend the flat ears of the clips that contact the PCB to increase contact pressure.  In addition, bend the rolled contacts that protrude through the cluster housing to close the gaps and increase contact pressure against the gauge pins.  Then reassemble and check the gauge function.

recoil:
I appreciate you taking the time to write me. 

Any chance I should connect the gauge to the battery directly to ensure it works before ripping out the gauge cluster?  I'm a noob so I just want to make sure I won't blow myself up if I test the gauge right against the battery itself.

:)

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