Ammeter to Voltmeter - New American Autowire Harness

[csfields]

OK, So I got my new American auto wire harness in, super great kit. I'm down to the gauges and obviously it states to run a voltmeter vs the stock ammeter. I am running stock gauge set with printed circuit board. I picked up a sunpro volt gauge, that I read with some slight mod, it will fit. My questions, has any one done this and how does it intergrade with the printed circuit board etc. Any help would be appreciated.

[JJH Jimmy]

I used a stock volt meter from a square body. I just pulled off the needle and drilled out the rivets that hold the square body face plate on and installed the volt meter in the same spot as the ammeter and used some small screws to hold it to the ammeter face plate. I then glued the ammeter needle onto the voltmeter.

As for wiring, I just cut the printed circuit and wired it to the temp. gauge.

[Husker]

Cool mod what year 73 and up?
Ron

[JJH Jimmy]

I got my volt meter out of an 85. I think 73's still had and ammeter but not sure when the switch was made.

[62 short step]

Originally Posted by JJH Jimmy

I got my volt meter out of an 85. I think 73's still had and ammeter but not sure when the switch was made.

I just did this to mine. Does yours peg all the way to the charged side when on?

[leftybass209]

Originally Posted by JJH Jimmy

I used a stock volt meter from a square body. I just pulled off the needle and drilled out the rivets that hold the square body face plate on and installed the volt meter in the same spot as the ammeter and used some small screws to hold it to the ammeter face plate. I then glued the ammeter needle onto the voltmeter.

As for wiring, I just cut the printed circuit and wired it to the temp. gauge.

Very clean! I like it. I followed the gringoloco version using a disassembled sunpro voltmeter with the stock face but I like the way your mounting looks much better!

[ray_mcavoy]

Originally Posted by JJH Jimmy

I got my volt meter out of an 85. I think 73's still had and ammeter but not sure when the switch was made.

Yes, GM continued to use ammeters in the 73-75 trucks. They changed over to voltmeters in 1976.

Originally Posted by 62 short step

I just did this to mine. Does yours peg all the way to the charged side when on?

Did you keep the resistor that was originally attached to the back of the voltmeter? And which of the 3 terminals did you connect to on the back of the voltmeter?

Here is the back of a typical 76+ truck voltmeter ... the resistor is the white rectangular ceramic piece with the blue paint in the center.



A is the +12V input. This terminal is not connected to anything inside the meter, but it is connected to one side of the resistor.

B is ground.

C is a connection point between the other side of the resistor and the meter's internal windings. This puts the resistor in series with the meter's windings.

The voltmeter requires the resistor for proper calibration. If you were to connect the +12V input to C instead of A, that would feed power directly to the meter's internal windings (bypassing the resistor) and will cause the voltmeter to peg to the right side of the scale.

[PowerdbyChevy79]

This is some good info...

[leftybass209]

Here is the back of a typical 76+ truck voltmeter ... the resistor is the white rectangular ceramic piece with the blue paint in the center.



A is the +12V input. This terminal is not connected to anything inside the meter, but it is connected to one side of the resistor.

B is ground.

C is a connection point between the other side of the resistor and the meter's internal windings. This puts the resistor in series with the meter's windings.

The voltmeter requires the resistor for proper calibration. If you were to connect the +12V input to C instead of A, that would feed power directly to the meter's internal windings (bypassing the resistor) and will cause the voltmeter to peg to the right side of the scale.[/QUOTE]

I just wanted to add some information to this. This conversion does work, I just finished it and ran my truck 10 minutes ago. It functions great, but needs to be wired as this states. It does need the resistor and will peg to the charged side if it isn't connected. The needle can easily be correctly aligned to as it reads correctly (also verified with a mulitmeter) but I'm sure that is relative to the condition of the gauge used.

[No8Easy2]

i pulled one of out a 87 truck, fits right in the cluster with no issues, wired up just as lefty said

[IMG][/IMG]

[davepl]

I like the idea. And I get the point. But don't we all just care whether the alternator is working or not, and that it's not overloaded and having to pull from the battery?

On a volt meter you'd see low voltage, on an ammeter you'd see discharge. When all is working you see 14.5 volts on a volt meter and neutral or charge on an ammeter.

Certainly a voltmeter tells you more, but either answers those two questions, so why is a volt meter better? What can you deduce from one that you can't from an ammeter, other than the overall charge of the battery when not running?

Thanks,
Dave

PS: Genuinely asking, not some passive-aggressive way of saying volt meters suck. Some of my best friends are volt meters.

[leftybass209]

I get your point Dave and it my experience a great working Battery gauge reads just to the right of center, and a system with issues (mine had) read center or just to the left. It wasn't discernable to me until it died on me. With a volt gauge and my other experiences (newer vehicles) when on the freeway let's say, if the alternator stops charging you will see the voltage gauge drop and "may" (I use may loosely because I don't Hawkeye my gauges) be able to pull over and out of danger. That's just my experience and reasoning.

[Andy4639]

It's the volt meter gives a better reading to the user only. As stated the amp meter leaves a lot of questions of to how well the battery is being charged. A amp meter will show the needle just past 1/2 way which is fine if the voltage regulator is working good and giving the battery full charge. May or may not be though?
With a volt meter it's just a glance at the gauge and you know!

[mtdave2]

I just got the same AA harness and discovered that the amp meter is not supported. ugh. another mod to my original truck? so, I get to choose to change the gauge wire the amp meter myself.

[csfields]

I did the conversion using a volt meter from Advanced Auto Parts or Autozone. Anyway you can break it down and use the guts of it on your stock ammeter gauge to keep the look genuine. Just need to remember the gauge layout in the event you have voltage issues. This is how I did mine. There is a thread on how to do it on here somewhere.

[88Stanger]

Thanks for posting this. I just purchased a square body volt meter to do this conversion.

[XwalkerX]

ha.

I did this over the weekend.

pulled the oem needle off the ammeter and put it on the voltmeter so it would match...

[deereboy8r]

Originally Posted by ray_mcavoy

Yes, GM continued to use ammeters in the 73-75 trucks. They changed over to voltmeters in 1976.



Did you keep the resistor that was originally attached to the back of the voltmeter? And which of the 3 terminals did you connect to on the back of the voltmeter?

Here is the back of a typical 76+ truck voltmeter ... the resistor is the white rectangular ceramic piece with the blue paint in the center.



A is the +12V input. This terminal is not connected to anything inside the meter, but it is connected to one side of the resistor.

B is ground.

C is a connection point between the other side of the resistor and the meter's internal windings. This puts the resistor in series with the meter's windings.

The voltmeter requires the resistor for proper calibration. If you were to connect the +12V input to C instead of A, that would feed power directly to the meter's internal windings (bypassing the resistor) and will cause the voltmeter to peg to the right side of the scale.

ray_mcavoy - My 1979 K5 blazer the volt meter stopped working on me and Ive been trying to get to the bottom of it and I do believe that the gauge is bad but wanted to make sure. On the back of the meter I have the connection for A and B but C there is no clip and I wanted to know if that was needed. I did check the A and B leads with my DMM and the clips read 14 volts while running. Any help on this I would greatly appreciate.

[Myoldtruck]

I just did the gauges over the winter. I used the autometer autogauge 2 1/16" I took the glass off of the new gauges, used model paint and painted over the autometer white lettering on the gauge, and repainted the needles orange. Kept the stock look. I added a vacume gauge in the blank 4th opening, and a clock in the center. I voltage gauge is only reading the voltage and you dont have a load going thru the guage like you do with a amp gauge.

[jocko]

Member TBone1964 offers these conversions in a choice of gauge faces, even a stock plain ammeter face or a stock ammeter face with voltage values added. http://67-72chevytrucks.com/vboard/s...d.php?t=653967

[paul blair]

I am thinking of installing a volt meter in the unused spot next to oil pressure gauge and leaving amp meter where it is! Anyone done this or know how to and what volt meter to use? No problem wiring-just locating the gauge and if it can be done on a 69 k/10.

[engineer_gregh]

Just another option, it also charges my phone.

https://www.amazon.com/gp/product/B0...d=AFHAE9RJVUMB

[paul blair]

Thanks greg! Quick and easy!

[ray_mcavoy]

Originally Posted by deereboy8r

ray_mcavoy - My 1979 K5 blazer the volt meter stopped working on me and Ive been trying to get to the bottom of it and I do believe that the gauge is bad but wanted to make sure. On the back of the meter I have the connection for A and B but C there is no clip and I wanted to know if that was needed. I did check the A and B leads with my DMM and the clips read 14 volts while running. Any help on this I would greatly appreciate.

Welcome deereboy8r,

That is normal for the 1976 & newer clusters (that originally used this style of voltmeter) to only have clips for the connections marked A & B on my photo. The C terminal only used as an internal connection point between the resistor (rectangular white ceramic block) and the coil inside the gauge.

The fact that you are reading 14V with your DMM connected to the clips in the cluster pretty much narrows the problem down to either the resistor or the voltmeter itself. For additional testing, you can switch your DMM to measure resistance and check the following:

(1) Measure the resistance between terminals A and C on the back of the gauge. You should get a reading somewhere around 127Ω if the resistor is okay. An open circuit reading could be due to a bad connection ... try gently re-tightening the nuts to see if that re-establishes the connection. If not, the resistor is probably bad and will need to be replaced.

(2) Measure the resistance between terminals B and C on the back of the gauge. You should get a reading somewhere around 122Ω if the coil inside the gauge is okay. An open circuit reading would indicate a bad coil and the only fix for that is to replace the voltmeter assembly.

[deereboy8r]

Originally Posted by ray_mcavoy

Welcome deereboy8r,

That is normal for the 1976 & newer clusters (that originally used this style of voltmeter) to only have clips for the connections marked A & B on my photo. The C terminal only used as an internal connection point between the resistor (rectangular white ceramic block) and the coil inside the gauge.

The fact that you are reading 14V with your DMM connected to the clips in the cluster pretty much narrows the problem down to either the resistor or the voltmeter itself. For additional testing, you can switch your DMM to measure resistance and check the following:

(1) Measure the resistance between terminals A and C on the back of the gauge. You should get a reading somewhere around 127Ω if the resistor is okay. An open circuit reading could be due to a bad connection ... try gently re-tightening the nuts to see if that re-establishes the connection. If not, the resistor is probably bad and will need to be replaced.

(2) Measure the resistance between terminals B and C on the back of the gauge. You should get a reading somewhere around 122Ω if the coil inside the gauge is okay. An open circuit reading would indicate a bad coil and the only fix for that is to replace the voltmeter assembly.

ray_mcavoy - That is exactly what I needed to know I did test for resistance before but only could get the 124Ω when I tested B and C but I just doubled check and sure enough open loop between A and C. I really appreciate the help and info!