Energized Utilities

Hi, New to the forum

I have a detached sub-panel in garage supplied by a single pole 15 amp 3 wire (one hot, one neutral, and ground)branch circuit from main in the house. Metal conduit ran underground about 30 feet from main to sub with a sewer later running along the same route, and old water piping that was disconnected from garage. In the four fuse old school sub panel rated at 60 amps the neutral and ground are bonded together. There is no grounding electrode at sub panel and I believe that I am experiencing energized utilities. Receptacles in garage test positive for ground but in house they test negative as to having no ground. Furnace and hot water tank randomly kick on and lights dim when washer, dryer or microwave is used. Any help would be appreciated

The neutrals and grounds should be separated in the sub-panel. If you are having the many issues in the home like you are stating you need to bring in an electrician to verify what is going on and repair as needed.
The age of the home may dictate a two wire system in the home but the garage may have been installed later on when 3 wire was introduced and required.