Battery voltage gauge no worky

[cleansquare]

Does this gauge run off the alternator? Or? Mine is not working with a new battery and truck running. How shoukd I go about troubleshooting it?

[ray_mcavoy]

No, it doesn't just run off the alternator. It reads the system voltage whenever the ignition is switched on. In other words, it'll show battery voltage with the key on / engine off and it'll show the alternator charging voltage with the engine running.

A common problem is the contacts on the printed circuit for the cluster plug. Even though the voltmeter shares the same power & ground circuits as the other gauges, it has it's own set of contacts & printed circuit traces. So a bad connection there will only affect the voltmeter and not the other gauges.

Check to see if the printed circuit traces have lifted off the plastic in the connector area and carefully glue them back down if necessary. Also check the contacts in the plug itself to make sure they're not bent or distorted. And use a test light or voltmeter to verify the power & ground connections (pink w/black stripe & black wires) to the cluster plug are okay.

If that all checks out okay, remove the front of the cluster, unscrew the voltmeter, and pull it out. There should be 2 metal clips in the cluster that made contact with the studs on the back of the voltmeter. Use a test light or multimeter to see if you have power between those two clips with the key on. If you don't have power there (and the cluster plug checked out okay), carefully squeeze the clips and pull them out. Clean any rust/corrosion off the clips & printed circuit contacts and snap the clips back in.

If you do have power at those two clips, check the resistor on the back of the voltmeter itself. Make sure the nuts holding it in place are secure (but not so tight as to crack the ceramic substrate). You can also measure the resistor with a mulitmeter ... If I remember correctly, they're close to 130Ω.

[cleansquare]

Originally Posted by ray_mcavoy

No, it doesn't just run off the alternator. It reads the system voltage whenever the ignition is switched on. In other words, it'll show battery voltage with the key on / engine off and it'll show the alternator charging voltage with the engine running.

A common problem is the contacts on the printed circuit for the cluster plug. Even though the voltmeter shares the same power & ground circuits as the other gauges, it has it's own set of contacts & printed circuit traces. So a bad connection there will only affect the voltmeter and not the other gauges.

Check to see if the printed circuit traces have lifted off the plastic in the connector area and carefully glue them back down if necessary. Also check the contacts in the plug itself to make sure they're not bent or distorted. And use a test light or voltmeter to verify the power & ground connections (pink w/black stripe & black wires) to the cluster plug are okay.

If that all checks out okay, remove the front of the cluster, unscrew the voltmeter, and pull it out. There should be 2 metal clips in the cluster that made contact with the studs on the back of the voltmeter. Use a test light or multimeter to see if you have power between those two clips with the key on. If you don't have power there (and the cluster plug checked out okay), carefully squeeze the clips and pull them out. Clean any rust/corrosion off the clips & printed circuit contacts and snap the clips back in.

If you do have power at those two clips, check the resistor on the back of the voltmeter itself. Make sure the nuts holding it in place are secure (but not so tight as to crack the ceramic substrate). You can also measure the resistor with a mulitmeter ... If I remember correctly, they're close to 130Ω.

Thanks for the info!

[cleansquare]

I have not tried testing the circuits for power, but I was cleaning the back of the cluster and saw that all the other gauges have 3 studs making contact with the board but the voltage gauge only has two. Did a clip fall out? Or does it even require 3 contacts?

[ray_mcavoy]

That's perfectly normal.

The voltmeter only has power & ground connections so it only needs 2 clips. The other gauges need 3 because they have power, ground, and a connection to a sending unit.

The voltmeter does have 3 studs on the back but only 2 of them are connected to the meter movement's internal coil. The 3rd stud is just used as a junction point and to attach the resistor.

I believe that 3rd hole in the cluster housing & printed circuit (where it looks like a 3rd clip would go) is sort of a leftover from the old 73-75 ammeter clusters. The ammeters had the 2 terminals side by side and didn't use that upper/middle location.

[cleansquare]

Got voltage at gauge...

[ray_mcavoy]

Okay, now check the ground terminal at the gauge. You can do that by connecting the clip lead of your test light to the upper/center clip at the back of the gauge and leaving the probe on the clip where you have it now.

If that checks out okay, the step would be to take the gauge out and measure the resistance between the posts.



Measuring between the posts I labeled "A" and "C" you should get somewhere close to 130Ω if the resistor is okay. If you get an open circuit reading, the resistor is bad or not making a good connection with the posts. Check to make sure the two nuts are secure but don't overtighten them.

Measuring between the posts I labeled "B" and "C" you should get somewhere close to 120Ω if the coil inside the voltmeter is okay. If you get an open circuit reading, the voltmeter is bad and needs to be replaced.

[cleansquare]

Thank u for the quick help. Between a and c I get nothing. Between b and c I get 124 ohms

[cleansquare]

Oh and I clipped the ground on the terminal ane the other one lit up hot still

[ray_mcavoy]

Originally Posted by cleansquare

Thank u for the quick help. Between a and c I get nothing. Between b and c I get 124 ohms

You're welcome. At this point, it sounds like the resistor on the back of your voltmeter is either bad or simply not making a good connection.

To rule out a bad connection, remove the 2 nuts and measure the resistor directly with your multimeter. If you still don't get any reading (open circuit), you'll have to replace the resistor. A few options for that include:

(1) Salvage a good used resistor off another 1976 - 1987(91) voltmeter. Or just use the whole voltmeter assembly if it has the faceplate style that matches the rest of your cluster. Note: the resistors on the other gauges are different.

(2) Napa offers some replacement resistors for GM gauges as part number NOE 7011498. But they don't give any details on the resistance so I'm not sure if they'd be suitable for your voltmeter or not.

(3) Buy a resistor from an electronic parts supplier. I measured the resistor on that voltmeter in the photo I posted ... it's 127.3Ω. The closest standard value resistor would be 130Ω and I don't think the slight difference would be noticeable. To install it, crimp on some ring terminals (like the Napa resistors) and use some nylon washers (or the old open-circuited ceramic resistor) as insulators between the the metal housing and the terminals. You want the resistor leads to make contact with the studs/nuts but not the metal housing on the back of the voltmeter.

[hatzie]

Crimp terminals are intended for stranded wire and don't hold well on solid wire without added encouragement. You may want to crimp and solder the rings to the axial leads on the resistors.