That seems correct, that side of ammeter should be labeled "-". Other pole "+" should have more than one wire as well. I didn't trace diagrams as you should find the correct one for your truck (which 54 I cant tell). Typical 2nd + wire is the horn fuse.

You can view/download/save a wiring diagram here:
http://chevy.oldcarmanualproject.com/electrical/wiring/index.htm

This might be for your truck:
http://chevy.oldcarmanualproject.com/electrical/wiring/pdf/54truck.pdf

Mikey

1951 Chevy 3600 rust bucket with GarWood dump bed conversion
http://www.flickr.com/photos/mikeybs51chevy