89 LX 2.3L - Turn Signal and Backup Light intermittently works

It could be a variety of things. Turn signal switch/multifunction switch, ignition switch, a wiring problem in the column. The first thing I would be looking for is a broken or loose wire since your problem is occurring with steering wheel input. You will need to remove the plastics and expose the steering column, then turn on the turn signals. Try to tug/wiggle the wires and see if you can get the signals to quit working. If you do, then you will need to track down a broken or loose wire. JRichter has been a good source on these forums and probably has posted or can provide a wiring diagram that would help you out.

The ignition switches in these cars are really problematic and can cause some weird and seemingly unrelated electrical issues. Since you are mentioning reverse lights, it is something to consider. I do not know what, if any, wiring is shared between the turn signals and reverse lights.