Another option that you may want to look at if you are set on installing an ammeter is to get an ammeter that uses an external shunt rather than an internal one so that the guage can be remote mounted and wired in with light wiring.
Here is a description of how they function
http://www.rc-electronics-usa.com/current-shunt.htmlAs an example of what is available here is a link to the Stewart Warner site that lists 3 ammeters in the same series of gauges, 2 require external shunts while the other has an internal shunt - if you look through their product catalogue you will likely find other examples.
http://www.sw-performance.com/products/HDAmmeterHere is a link that shows a picture of a 100 Amp shunt, they only offer 1 other part # that is good for either 150 or 300 Amps - maybe 12 or 24 volt application??.
http://www.sw-performance.com/index.php?page=details&p=407616I went to their site because I knew that they offered the 2 styles of Ammeter and just wanted an example of the technology that you could see. I am sure that other instrumentation suppliers offer similar options if this is what you want to do.