Not starting issue, also interior lights for radio, door handle, horn, have stopped working?

Most times the hard starting is due to the rotor tip seals letting oil in while the engine sets, then you try to start it and it fouls the plugs. By turning off the fuel it can help some because you can somewhat clear the buildup out by cranking it and distributing the oil as well.
Electrical wise, I hate to say it but even in a garage you could have critters, but the more common thing is simply time and corrosion in the old-style connectors. About the only solution that works on classics is to start at one end, go to a connector, open it up, inspect it and spray in some DeOxit. It removes the thin layers of oxides and when you reconnect it stays in place to help prevent further corrosion. When it comes to switches and such it also works in those. It's a lot of work but I have seen some amazing results doing it on my vintage cars. The only good thing is that being an 87 it isn't as bad of a harness as a modern car.
The reason it is worse in the heat is simple. In the colder/damper weather the conductors will shrink in a miniscule amount and improve the connection just enough that it works.
I would start there. Also, clean and redo all the grounds where they bolt to the chassis. It's a shock sometimes just how poor the connections get over time.