1969 Charger--Convert Ammeter to Voltmeter

[Chatt69chgr]

Has anyone hired Redline Gauge Works to make this conversion?  What did Redline do and what did they charge?  I'm asking here since I can't get Redline to answer the phone. 
There would appear to be two ways to do this.  One is to buy a small voltmeter (like a Bosch 8215) and do the appropriate mechanical engineering to fit it into the existing rallye dash hole.  They second would be to just use the existing ammeter.  Disconnect the wiring to it and install a resistor in series with the ammeter. Glue a new scale onto the existing ammeter faceplate.  I'm not sure what size resistor would be required. Maybe use a variable resistor like a 500K or 1 Meg Ohm potentiometer in series tied to a 13.6V source and vary the resistance until the gauge needle is at the midpoint.  Remove potentiometer and insert fixed resistor.  Then vary the voltage source and note the gauge needle positions for say even voltage increments from 8-14 volts?  Would need to make a paper gauge face to glue to the existing gauge. Just a thought.
So has anyone chased this rabbit? 

[b5blue]

I think Dino did that? 

[John_Kunkel]

https://www.youtube.com/watch?v=JtXOS_jOHfQ

[Chatt69chgr]

The URL referenced by John Kunkel was just purchasing a 2" voltmeter and mechanically installing it in a rallye dash slot where the ammeter resides. 

I will probably try what I suggested but need to buy a good regulated power supply.  The one I had went south years ago.
 One would need to remove the existing shunt on the ammeter and install at least a 1 Megohm pot in series with the ammeter movement.  I used to have a lot of electronic parts laying around but not sure what I have left anymore.  If, and when, I ever get around to playing with this idea I'll post the results.

[marshallfry01]

Redline did the conversion on my gauge cluster. Looks fantastic. You'd swear it originally came with a voltmeter gauge. I can't remember the price... I had them do a lot of other things as well. I tried doing the conversion myself but electrical is not my area of expertise and I didn't want to screw it up. You sound like you know a lot more about electrical than I do though.

[Kern Dog]

I tried to do a workaround and get the guy at Redline to just send me a new face for my gauge. They only wanted to do the whole conversion.
I was trying to save a few bucks and Shannon saw through that....
I can't blame him. He has a business to run. I was just trying to do it cheaper.

[John_Kunkel]

One would need to remove the existing shunt on the ammeter and install at least a 1 Megohm pot in series with the ammeter movement.

Maybe I'm not following your plan. You do realize that the ammeter is more than just a meter? The current that operates most of the car's electrical components flows through it...so putting a resistor in SERIES would lower the voltage going to those components and render them inoperable or damage them.

[Chatt69chgr]

I would not run the car's electrical system through the ammeter anymore. In other words, I would bypass it and would do this in the engine compartment to keep from having all current going through the bulkhead connector.  Then remove the shunt on the back of the existing ammeter gauge.  Now it is just a d'Arsonval meter movement. A source of 12 volts under the dash that exists when the key is ON would then be wired to the ammeter with a resistor in series with it.  This should work.  Just need to select the proper size resistor.