I got a 30 amp panel meter with shunt from

Centennial Electronics, Inc
2324 E Bijou st
Colorado spings, Co 80909

800 320 4666
719 633 4666
www.centennialelectronics.com

The # is AIM 6030A. The shunt for this meter would bypass enough current to protect your ampmeter. I think it cost me about $20.
Install the shunt in parallel with the posts on your ammeterand it should work fine.

I have a spare if you cannot get one from Centennial.

1954 Chevy Half-Ton
In the Stovebolt Gallery
More pix on Shutterfly
More pix on Photobucket

1958 Chevy 1/2-Ton Stepside
In the Stovebolt Gallery
More pix on Photobucket

<> + <> + <> + <> + <>
"Time's fun when you're having flies." ~~ OLD FROG