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71-74 Amp meter to volt meter conversion

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DMack View Drop Down
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    Posted: Mar/02/2020 at 6:26pm
Hey all,

I did a swap from an amp meter to a volt meter on my 71-74 AMX cluster.  Thought I'd share how I did it, just in case someone else is thinking of doing it.  First of all, I am not a "purist" that thinks everything needs to be an AMC part if its on my AMC.  I just want stuff that works and "looks" right.

I did this swap because I heard all the horror stories of the old amp meters getting so hot they melt the dash or even start a fire.  First quote I got to change it from an amp meter to a volt meter was $280.00.  So being the stingy son of female doggy that I am, I figured I could blow at least a $100.00 trying it myself.

I did the research and landed on a 52 mm "Smiths" voltage gauge.  The needle is hung from the top of the gauge, just like the factory amp gauge and the size is pretty darn close. Model is #ABV2220-00B
I bought it online from a British parts dealer by the name of Caerbont Automotive Instruments.  They make reproduction gauges for Jaguars & Triumphs.  After the conversion from British pounds to dollars it cost me $61.58 for the gauge delivered.  Only took 4 days to get to me.

Below is what it looks like. 



After I got It, I took it all apart until I got it taken down to this point (below)



Next, I carefully cut the actual edge off of the gauge face with a Dremel tool.  Next take the factory amp meter out and remove the orange indicator needle.  I cut the needle off right where it bends (when its in the amp meter) and stuck it on the new gauge with a light brush of contact cement.



The posts on the back are about a 1/4" wider than the posts on the amp meter, and the new meter posts need to sit up about a 1/4" higher as well.  Also you need to trim out just a bit of material from where the back of the meter makes contact with the gauge.  A little "bit by bit" trimming and the gauge will slide into place.  also there is a triangular shaped piece that I removed, hidden behind the printed circuit board.  



Next was the face of the gauge, I took a picture of the oil pressure gauge and took it to a local sign company that does small vinyl graphics.  I had them invert the (curved) scale and asked them to put a longer hash mark at the "13" position.  Then asked them to put in the "11", "13" and "15" on the scale... $27.50 to do the proof and print me 2 decals.

This is the result.


The new gauge has a stop post on the left side at the 11 volt mark.  So I bought a leather punch at Home Depot and popped a hole into the decal before I slid it into place.

Here's what it looked like before I put the gauge all back together. You can see where I trimmed the triangular shape in the bezel.



And here is the result when it went all back together.



In the picture it looks like its "lighter" than the other gauges. but actually its just how the light was hitting it for this pic.  Here's a closer pic.  you can see my punched hole is off by just a hair.


So when it was all said and done I had right at $100.00 into it including the new leather punch.  I think it turned out pretty nice, and doesn't generate any heat.  I happened to have a cluster that had the extra 12 volt stem on it for a low fuel alarm, So I used that as the ignition supply line for the new volt gauge and then just tapped into the printed circuit ground for the other side of the gauge.

Best part...It works perfectly... You might also notice that I replaced the "machined" face for a hex pattern wrap available from 3M.  Stuff is super easy to put on and very forgiving.  I've put it on the dash, shifter cover and both door panel areas where the original machined panels were located.

If you like the look, let me know and i'll be happy to send you the link for the wrap.  

Thanks everyone for all the great tips!!

Dave





Edited by DMack - Mar/04/2020 at 11:53am
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garweb3 View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote garweb3 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2020 at 6:34pm
Great job. Looks like it came from the factory that way.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2020 at 7:15pm
Nice work
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2020 at 7:23pm
Looks great Dave! But it's hard to look at sideways. Confused Wink I ordered 2 gauges yesterday, one for Kevin and one for me. Thanks for sharing this with everyone. Cool

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Post Options Post Options   Thanks (1) Thanks(1)   Quote AMXFSTBK390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2020 at 7:38pm
Nice idea. You do good work. Hope my neck recovers. LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FritzF3 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/02/2020 at 7:52pm
Dave,
What about the 'amp' lettering?

Edit. 
My bad. It says 'alt'.


Edited by FritzF3 - Mar/02/2020 at 7:54pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2020 at 9:44am
Originally posted by DMack DMack wrote:

I did this swap because I heard all the horror stories of the old amp meters getting so hot they melt the dash or even start a fire.
As a point of clarification, meter movements use very little power, so they are not getting hot. It's the connections to the meter that are getting hot. Resistance causes heat in an electric circuit because it is dissipating energy. Lots of current with a little resistance equals heat. In the case of these "alternator" gauges (and not just on AMCs), all the vehicle's current is routed through the two terminals on the gauge, but all of the current does not run through the meter movement. The movement uses a shunt to divide down a calibrated amount of current to run the needle.

The theory is sound, but the implementation is problematic in a semi-controlled environment. Under the dash is sheltered from rain, but it's dusty and the temperature can fluctuate wildly. Dirt in a connection creates resistance, and any connection in a vehicle electric system will get dirty. The higher the current in that particular circuit, the better the odds it will cause a problem. With these ammeters, it's the connections that get hot. Unless the meter movement itself goes dead, there is no need to replace it, just clean the connections to it and all should be good again.

DMack has done a wonderful job on the conversion from ammeter to voltmeter. I am NOT criticizing him for doing it, just pointing out that it was likely unnecessary because all he did was substitute one meter movement for another. Granted, he did eliminate two high current connections in the wiring harness which improves reliability.

For purists, there is no need to panic. Keep the terminals clean, inspect the cable jacket for cracks (they do dry out over time) and your factory gauge should be fine.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2020 at 12:00pm
Originally posted by FritzF3 FritzF3 wrote:

Dave,
What about the 'amp' lettering?

Edit. 
My bad. It says 'alt'.



For mine, I made a template to go over a standard face, I can show my image once I find it. Mine used a fuel or temp gauge, with resistor to be used as a volt meter. Just trimmed the needle and mounted in the amp meter location.



Edited by 304-dude - Mar/03/2020 at 12:07pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote DMack Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2020 at 1:10pm
Thanks everyone for the input.  

Tried to rotate the pics, but couldn't seem to get to a position the Forum liked and would accept.  I'll have to play with that a bit.

I stopped this morning and asked my printer if he'd make me three more decals.  $25.00 is their minimum run. I've received several requests for the decal.  I'll let you know as soon as I've got them and I'd be glad to mail them out (How about $9.00 including postage?...not looking to make anything just glad to help the AMX cause) if this is the way you'd like to go.  Just PM me with your address.  I'll check and see if the printer will give me a break on making a "sheet" of them if I get enough interest. 

Just a side note, If I did this again...I might try mounting the decal on a really thin piece of steel or aluminum and then glue that onto the face of the gauge face itself.  Just to keep it nice and flat.

Thanks again and I'm glad you guys approve.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMack Quote  Post ReplyReply Direct Link To This Post Posted: Mar/03/2020 at 4:46pm
Originally posted by 304-dude 304-dude wrote:

Originally posted by FritzF3 FritzF3 wrote:

Dave,
What about the 'amp' lettering?

Edit. 
My bad. It says 'alt'.



For mine, I made a template to go over a standard face, I can show my image once I find it. Mine used a fuel or temp gauge, with resistor to be used as a volt meter. Just trimmed the needle and mounted in the amp meter location.


Thanks 304 Dude... I actually did your suggested solid state mod on the Instrument panel voltage regulator.  Works like a charm.  many thanks...
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