last week my fuse broke by accident and i replaced it with a 5 amp fuse ,like it said on the fuse..
hope this helps
PS: this is the BLACK wire that you mean isn't it (drivers side)
1972 Chevy Pickup longbed 502ci Th400
"IF IT AIN'T BROKE DON'T TRY TO FIX IT"
(I'm sorry if the spelling isn't correct,i'm trying the best I can )