I need to put in a new AC in my 77 HiLo, but concerned about electrical issues.

Any advice?

If it had ac it should be plug and play. 15amp breaker is probably what it has and should be fine. IMO replace with the same BTU unit.
One good thing is newer "usually" means a more efficient unit.

Rick

shouldn't have any issues if replacing the a/c,maybe a little more work if added a/c.

__________________
Les & Patricia
2006 22ft towlite (replaces 97 21TL)
2006 Toyota tacoma pre-runner 4.0 L V-6 quad cab
w/ 98 chevy Powervision towing mirrors
2017 Chevy Silverado 1500 5.3 v8 (replaces Toyota)
2 Hobie mirage pedal drive kayaks

Might want to check the "starter set" under the hood on AC unit
I found a universal set at local RV dealer and replaced in myself with minor experience(I am 73) and it has worked like new last 2 years.