Here is how to wire the charging system into the ammeter.

http://chevy.tocmp.com/1942_47shop/4247csm1208.htm

And here is an overall wiring diagram. It's not for a '49, but it's pretty close and will give you a general idea of how to go about doing it right.

http://chevy.tocmp.com/1942_47shop/4247csm1232.htm

and here's a better version:

http://chevy.tocmp.com/chevywiring/diagrams/1946truckwiring.pdf

~#~#~#~#~
1946 Chevrolet 3600 - "Old Number Seven"

Cavalry's Here. Cavalry's a frightened guy with a rock, but it's here.