Oh my, what a challenging question!
It's definitely possible and I can picture several different approaches. I'm not at all sure which will work best for you.
One option is to move TRH into a related table. Then multiple items of equipment can be linked to the same TRH record (or just 1). Just what you needed, another related table right? But such is the nature of relational database design...
Haha yes challenging alright and absolutely, really wanted another related table :)
Is the one above you described the simplest and easiest? Would I make a new table occurence of Service Histroy (child table) and join it to the Equipment_List (parent) table? How would I make the connections so the above is possible?
The other thing is I have table occurences of Service History (say SH1, SH2, and SH3) that are connected to Service History, so by taking TRH out of the main Service History table and putting it in a related one, will that effect SH1, SH2 and SH3?
I am a little worried this might be a little too much for me to handle.
I think it's probably the most straight forward way to handle this. Your TRH table can have an auto-entered serial number field to uniquely identify it and then you can link any given equipment record to it by assigning the __pkTRHID value to it's _fkTRHID field. This implements a "many to one" relationship.
so by taking TRH out of the main Service History table and putting it in a related one, will that effect SH1, SH2 and SH3?
It could, depending on the needs of your system, you may end up with multiple occurrences of the TRH table so that you can link it in to each of these service history occurrences. (But note that you can link this to the equipment record rather than the SRH record.)