OK, 1976 is a completely stand alone year, and no other harness will even come close to working on it.
The main difference is how they reconfigured the charging system and gauge cluster.
Trust me on this..you DON'T want to fix it!
Very trouble prone year for electronics.
If it was my car, or was doing this for a customer, I would retro fit a 1975 harness and gauge cluster.
Your under hood wiring can be made to work with the 75 harness.
I actually have one of those listed on here now, but that has nothing to do with recommending that.
If you were starting from scratch, I would probably go with a full set of harnesses from a 70-73 car.
Much simpler and easy to work with.
BTW, 75 is the only year that will be compatible with the rest of your cars wiring because of the change in connector plug style that happened in that year