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Bad gauge cluster voltage regulator? Easy $2 fix.

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Sorry, didn't check back enough posts. If not compatible maybe the components can be jumbled around to tune it to the correct regulated voltage???

The voltage regulator IC used for that can be found in a variety of output voltages so it is pretty easy to change. 5v is used for the gauges on a 1965-66 Mustang instrument cluster. Linear voltage regulator L7805CV would work. For the early Mustangs I'd probably modify the simple circuit here to filter the input slightly using at a minimum a bridge rectifier and a couple of capacitors on the input. The Mustang aftermarket is extremely well supported and you can buy these all over the place although usually in the ~$40 range.

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aintnobiscuit did it work ok on your 521? any pictures?


No, unfortunately it didn't work. The gauges only read from about 25% -> 50% instead of from 0 -> 100% full but this truck has weird wiring problems I haven't had time to sort out. I moved to hawaii and didn't bring any cars... just came back so here I am. Can't wait to start working on the truck again.

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Datzenmike please remove if you think this should go to the classifieds. This is not a for sale post just a feeler post.


First I'm not taking orders, I just want to know if there is interest enough in these to justify me ordering parts and building them for sale.


I've built and sold the voltage regulators in the past, there is a picture earlier in the thread of my old one I built.


I'm thinking of building these again and doing some minor improvements to the design also. Mostly add a reverse voltage protection and a little bit of filtering (e.g., a diode and capacitor on the input). This would up the cost of materials (2-3 times) and the time to build each one. The improvement would be the increased ability to survive reverse voltage if hooked up wrong. Downside is more expense on materials, longer time to assemble, and slightly bigger final size.


Most likely shipped cost would probably be at least $20 due to increase in time and materials.


Last time it was a bit of a pain in the ass all things considered, and I only made a couple dollars per and had to drive to the post-office each time.


Shipping was the most expensive part and going to the post-office each time was not fun. I can't mail from my house, every time I tried they would just disappear into the mail system and I would have to send out a replacement, only for them to show up months later. Most of the regulators sold to people not on the forum.


So is this something people would want? Is it worth me buying the parts and building these for sale?



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On 4/16/2013 at 11:57 PM, aintnobiscuit said:



You're temp/fuel gauges don't work and you've already checked the output from your fuel/temp sensors to make sure they are not the culprit. You checked continuity of the wires from the sensor to the gauge and the output from the current voltage regulator to find out that it outputs the wrong voltage, none at all or it's fluctuating. Well guess what, I have a solution for you!


I recently found out that my gauge cluster didn't have a voltage regulator, which is why my fuel/temp gauges don't work. Well that's totally unacceptable for me because i want to run all the stock gauges in my 510. It would bum me out to have to run aftermarket gauges when I have perfectly good gauges already in the cluster.


Fast forward to a few posts and questions later I learned the following.


Some basic info needed to figure out the problem

  • The gauge cluster needs ~ 9v to power the fuel and temp gauges
  • The car is DC and runs off 12-15v (i'm only putting this for people who may not know)
  • Without a voltage regulator, the gauges do nothing

How the sensors work with the gauge cluster


The gauges always have power. As temperature or fuel level rises/lowers the resistance in the sensor changes. It allows more or less current to pass through it to the chassis ground. Both sensors work in the same way.


So the problem is we just have the wrong positive voltage going to the gauges... Well all the voltage regulator does is keep the voltage constant given any input power. OK... What are some options? I personally didn't want to buy a whole gauge cluster just for the voltage regulator. I have a background in basic electronics and arduino stuff, so I started searching mouser electronics, digikey and my local parts place marvac.


I found out something awesome.


There are a million really cheap tiny voltage regulators that do the same job as the big metal one on the back of the gauge cluster. Average cost? ~$0.43 to $2.00.


Well that's bad ass isn't it?


I picked up two just to be on the safe side and a PCB (printed circuit board) and set to working.




  • Voltage regulator
    • NTE1910 or
    • LM7809
  • Wire (preferable 3 colors)
  • PCB board (optional but makes it nicer)
  • Project box (optional but makes it nicer)


Explanation of pins on the voltage regulator




Here's a picture of the voltage regulator for reference.

  • Pin on the far left is the power input (in our case 12-15v)
  • The center pin is a "common ground". Just connect it to your chassis ground
  • The far right is the power output (9v)

There are some upgrades you could do to stabilize the signal by adding capacitors, but i honestly didn't think it was a big deal. this isn't the biggest deal in the world, it's a gauge.


Tools needed


  • Soldering iron
  • Solder
  • Multimeter (handy but not necessary i guess)
  • Third hand tool
  • Dikes to cut the wire
  • Wire strippers
  • Electrical tape
  • Black wire*
  • Red wire*
  • Another color of wire*
  • Project box (optional)

*Solid core wire would be best in my opinion for this project since it is not designed to be moved around a lot. Additionally, pick a wire gauge that will fit through the holes in the PCB.*


Setting up the voltage regulator on the PCB


If you're not good at soldering tiny wires, pick a PCB with larger spaces between each hole or spread the pins, being careful not to break them so you have a hole in between each pin. That should be plenty of room to solder comfortably.


  1. Place the voltage regulator on the PCB, bend it so it lays flat against the PCB and solder all three pins.
  2. Place the red wire in the hole in front of the power input pin (far left) and solder it.
  3. Place the black wire in the common ground pin (center) and solder it.
  4. Place the 3rd color wire in the voltage output pin (far right) and solder it.
  5. Connect the power and ground pins
  6. Test the output power pin with a multimeter to confirm ~9v.
  7. Hook up output power to your gauges.
  8. Have a beer.

That's it. Easy right?


Finishing touches / final thoughts


  • Placing this into a project box would be a good idea to keep wires from being broken/bent
  • If you cut down a PCB to a smaller size, sanding the edges will make it look nicer
    • Score both sides of the PCB with an exacto and you will be able to snap it like a cracker




Checked the battery for static test



Third hand tool is nice for soldering PCBs with tiny holes.



This is an idea of how small the VR is compared to the old school one.



Didn't want to fry my gauges so I checked the output before hooking anything up



Testing my gauge... SUCCESS!!!!



So tiny ? I'm so glad I can now finish putting together my gauge cluster. 



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I see you quoted, what's the question? 

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On 8/30/2018 at 8:35 AM, Mike454SSLS6 said:

None of the pictures are showing to be available. Is this the voltage regulator on the back of the speedometer? https://www.classiczcars.com/forums/topic/56560-240z-gauge-electrical-problem-again/ If so, there is a green wire and a green & red wire. Are they both regulated? Thanks in advance. 

So, not to beat a dead datsun, mike is right. The pics dont work. Im experiencing the same issues. Does anyone have any pics they could provideto help a feller out?

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I figured it out. Sorry, I should have taken some pics but just pull the speedometer out and that box is the regulator. Don't worry about the orange wire (or at least I didn't). Cut the two green wires and wire your voltage feed wire to the new regulator input, the other one to the 9volt output. There's a ground wire that was already there. The regulator will ground to that. Done, and works great. Thanks for the original write up. I spent a significant time tracing this wiring problem. 

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Hi everyone. I don't have these pictures anymore and the post is from a long time ago. I also don't have any datsuns anymore so I don't frequent ratsun, but when i get my next one i will again.


Here's a picture that should help people with all the questions re: where is the voltage regulator from a quick google search.


Hope this helps!



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