First off you won't melt your ammeter unless you put an insane current load on it. It will only output the current your system calls for. I'm running 60 amp 6v alternator on my 38 and have had no issues in two years. If you run the return wiring through the ammeter as suggested by J-Dude you should have no issues.
I routed a heavy wire from the alternator on my 38 straight to the battery because I'm experiencing excess resistance when going back through the normal wiring and I'm too lazy to crawl my fat a$$ under the dash to figure it out. I too show a slight discharge on the ammeter but it's to be expected when you augment the wiring in that manor. Electricity will take the path of least resistance from the alternator to the battery which is the heavy wire not running through the ammeter. Any current requirement on what would normally be (had you not bypassed it) the alternator side of your ammeter will pull that current through the ammeter the wrong way, thus showing a discharge when it's not actually discharging. Clear as mud??
