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coolioni

Fuel gauge and temp gauge not working

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Do you guys think it is worth trying to get it fixed, or just go with aftermarket gauges ?

The fuel tank is fairly new, so it must something with the wiring or something in the dash.

As far as the temp gauge I think it is in the dash too.

What can I try to get them to work ?

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coolioni you should put your vehicle in your signature so everyone knows what you have. I looked it up and assume we are talking about the '83 720?

 

The chance of both gauges and or senders going bad together is, well extremely rare. There is one thing that they both have in common and that's a voltage regulator built into the gauge cluster. I have the round 720 gauge cluster and yours is likely square. I'm not even sure where it is in the cluster. The 620 has a removable module. I don't think the 720 does, at least without taking the gauges apart. It's possible (maybe) that just unplugging the gauge connectors in the back and then connecting them will clean the connection and get them going, but...

Edited by datzenmike

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I have taken the dash out and replaced all the black background with white backgrounds. When I did this I had to unplug the cables , and at the time I replaced all the lights and also cleaned up everything.

Even after doing this only one more light lit up.

There are a couple of lights still not working.

I bought these cool blue LED lights that light up your dash real well at night so you can see everything.

I did think any of the connectors are bad, it may just be something in the dash itself.

The odometer ,speedometer, and rpm gauges still work, but the temp and gas gauge does not.

The oil pressure and voltage meters in the ceter console work just fine still.

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x2 what Mike said:

 

The chance of both gauges and or senders going bad together is, well extremely rare. There is one thing that they both have in common and that's a voltage regulator built into the gauge cluster.

 

620's and earlier Datsuns had a removable module like I posted in another thread:

 

http://forum.ratsun.net/showthread.php?t=6923

 

I once found a how-to on replacing the solid-state voltage regulator for a Z, which might be similar if not identical for a 720. Googling now....

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my temp hasn't worked since i bought my 510, but thats because the thermostat housing where it plugs into is destroyed. the fuel works when it wants to, i would imagine its a ground. strangest thing is the autometer tach and fuel gauge work when they want to at the same time. when the tach works - so does the fuel.

 

i'm starting to wonder if its the fuse box, which is tempermental at best.

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I was thinking of bringing to this one local guy that is a pro at wiring with just about all cars made.

Maybe he can figure it out.

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My 521 had no temp or fuel too. I cleaned every conection and even took apart the voltage regulator on the back of the gague pod. The regulator looked fine. But I replaced it anyway, and sure enough it fixed the problem just like that!

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My 521 had no temp or fuel too. I cleaned every conection and even took apart the voltage regulator on the back of the gague pod. The regulator looked fine. But I replaced it anyway, and sure enough it fixed the problem just like that!

 

Always check the simple shit first. You don't have to be an electrical genius, and you'll be surprised how often it resolves the issue.

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Yep, check the fuse box. They share a fuse. Maybe the wiring connection in the fusebox is bad.

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yup it was the fuse box. pain in the ASS to unscrew it after the heads were rusted and stripped. but once freed, things came back to life! now i dont have to worry about driving too much too far wondering if im on fumes or not!!!

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I recently removed my dash to replace the pad on my 620 and now my fuel gauge and temp gauge isn’t working. Where on the gauge cluster is this module you guys are talking about is it the same as the regulator in the gauge. I tried to clink on a link in this discussion but says it no longer exists.

Edited by superbee620

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The 521 truck has a small external plug in volt regulator on the back of the gauge cluster, the 620 does NOT. It's internal and the gauge has to come apart to get at it. It appears to be in the temperature gauge and works both gauges

 

Qn51VX4.jpg

 

Seems unlikely this would stop working just because the dash was removed to work on it. It's much more likely that the dash wasn't plugged in properly.

 

Are any of the other lights not working? If turn signal lights work then not the power for the volt regulator. Seems very unlikely only the lead to the temperature and gas tank senders are not making contact but they share a common ground.

 

Try to unplug the large round 12 pin connector in the back and plug in again, are there any other plugs that need connecting? Maybe a ground?

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Ok I got the engine in . All my lights are working and all fuses checked with test light are working. But still no fuel gauge or temp gauge. I checked all my connections they are plugged in correctly. Cleaned my ground from head to battery and ground from body to alternator bracket. You mentioned these gauges run off the same ground. Which ground would that be ? Any other areas to check before I pull the gauge and replace it with a spare.

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The gauges work off the same voltage regulator that provides about 8 v. If they ran off the battery they would see anywhere from 11 to 12 when not running to 12-13 when idling to 14.5 when revved up and driving which would throw the gauges way off. With a steady 8v the gauges are overall more exact.

 

The flow is from

 

Battery 12v ....> regulator 8v....> both gauges......> temp and gas senders....> ground.

 

The senders are a variable path to ground producing a meter reading. For example the gas tank sender is 10 ohms or less for a full gauge reading and 80 ohms or more for an empty reading. The temp sender would be similar.

 

 

 

Qn51VX4.jpg

 

If both not working then expect the regulator. It's primitive but works. On the TEMP gauge there is a bi-metallic strip with contacts and a fine white wire wound around it. Power is applied, the wire heats up, the strip warps from the heat and the contact opens, the strip cools and bends back making contact and begins again. The brass contacts can become corroded/tarnished. Fold a strip of fine sandpaper so that it's rough on both sides. Gently pull the contacts apart and slide the sandpaper between them. Let close on the sandpaper and pull sideways out from between to polish the contacts. Two or three times should do.

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On ‎11‎/‎11‎/‎2019 at 10:58 AM, datzenmike said:

The gauges work off the same voltage regulator that provides about 8 v. If they ran off the battery they would see anywhere from 11 to 12 when not running to 12-13 when idling to 14.5 when revved up and driving which would throw the gauges way off. With a steady 8v the gauges are overall more exact.

 

The flow is from

 

Battery 12v ....> regulator 8v....> both gauges......> temp and gas senders....> ground.

 

The senders are a variable path to ground producing a meter reading. For example the gas tank sender is 10 ohms or less for a full gauge reading and 80 ohms or more for an empty reading. The temp sender would be similar.

 

 

 

Qn51VX4.jpg

 

If both not working then expect the regulator. It's primitive but works. On the TEMP gauge there is a bi-metallic strip with contacts and a fine white wire wound around it. Power is applied, the wire heats up, the strip warps from the heat and the contact opens, the strip cools and bends back making contact and begins again. The brass contacts can become corroded/tarnished. Fold a strip of fine sandpaper so that it's rough on both sides. Gently pull the contacts apart and slide the sandpaper between them. Let close on the sandpaper and pull sideways out from between to polish the contacts. Two or three times should do.

 

When servicing old teletype machines you would follow up this procedure with a few quick wipes of a piece of magazine cover to polish the contacts and prolong service life  "Life magazine" was the cover most preferred.

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Just wanted to update my problem with temp and fuel gauge not working.

I pulled instrument panel out dissembled speedo unit .removed and checked temperature gauge . Where the contact/ points come together the arm was bent off to one side and wasn’t making a solid contact. 

Maybe could have bent arm back and sanded or filed contact for good connection but I had a spare speedo unit and just replaced temp gauge. Both fuel and temperature gauges are working correctly now.

Thank you datzenmike and mikeRL411 for the professional advice. 

😎👍

Edited by superbee620
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