Interesting share from the excellent One Man & His Mustang blog
The blog post has a really good detailed approach on how to replace the ammeter with a voltmeter all whilst keeping the stock appearance.
Since I have owned the car and knew I would have to re-wire it I knew that the stock ammeter was not going to be a working option. My American Autowire Upgrade loom strongly recommended not to use it as well. The main reason they don’t recommend it is that the single wire alternator I now have is 100amps and not the tiny 48amp as stock. The amount of amps going to the ammeter would probably melt something and destroy my car via a fire. This leaves the options very limited to say the least, I could blank of the hole which would look rubbish, put a clock in there, better but not ideal or find somebody who has done some work to make a bespoke gauge very expensive I expect. I have investigated if anybody has done this before which of course they have with various results. They can look out-of-place being new with old, or only seem to work with the stock loom, again not an option for my upgrade wire loom. Many hours and thoughts have gone into looking about in old car accessory shops, online and eBay, and I think I have found a good alternative to the stock ammeter. I purchased the gauge from eBay in the end and it was shipped over from the far east which only took a couple of weeks to get here. My thoughts were along the lines of, it’s not a lot of money to wreck the meter if I have too and its worth a go. I gauge I found a VDO gauge that was plain black and white and the style of letting matched the stock gauge look. There is a wire from the back that will light up the meter via single white LED to only show up the gauge range at night so it wont flood the rest of dash. The only down side I could see was this was a big gauge depth wise due to the casing and the fulcrum of the gauge was at the bottom not the top as the other gauges.
This modification was going to require me to drill the back of the dash case. I made the decision this would be worth it. If you don’t want to drill your dash case back then this not for you! Obviously not concours but you will not see the drill marks from behind the dash, yeah I will get the anoraks saying “ooh, that’s not a genuine part is it?” My car is not going to be stuck in a garage cleaned and put away again, my car will be driven and enjoyed, that gauge will help me identify if there is a problem.
Tip: Before I started this little project I did check the gauge to make sure it worked. I crocodile clipped The terminals and touched the terminals. Which sprang the dial into life.
You can read the full article here