I've been having this problem for a couple years, but I live in CT so it doesn't happen that frequently.

When it's hot out, 90+ degrees, I have to use the shift override button to put my car into gear and the turn signals won't work.
Recently, I learned that if I go over a significant bump (thanks to the contruction on I95) everything starts working again.
Also, after I've driven for a little bit, shut off the car and restart it, it most of the time will be resolved.

Any ideas?

I just got back from CT this afternoon and the thermometer here said 99F in the shade with the dew point at 71. Ouch!
I know what you mean about the expansion bumps on I95. We rented a Merc Gran Marquis POS, and there are no bumps on I95! Can't feel the front wheels through the steering wheel either!
You problem sounds exactly like an ignition switch failure. You need to remove the plastic cover around the steering wheel, unscrew the 2 screws and pull off the ignition switch, and put on a new one. FCPGroton has a good selection, just drive over and get one. Too bad you have to pay sales tax, but no shipping is required.
BTW, gas at LaGuardia airport was $3.32, in Greenwich it was $3.53, and in Waterford is was $3.29. And when I got back to the TwinCities it was ONLY $2.91 for regular.

Klaus
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(V♂LV♂s 1995 854T, 1998 V70R)

I hear you about the gas, I drove down to PA this weekend and paid $2.77 for reg outside of Allentown, I paid $3.35 teh day before here in fairfield, ct

I would look for a loose connection behind the kick panel under steering column on driver's side. Do your brake lights always work? The switch on the brake pedal and some steering column wiring might run together. If someone worked under there before maybe they did not reseat a connector well. I had such after replacing an a/c evaporator - many unrelated symptoms appeared together and I had not pushed in one of the big connectors fully when reinstalling.

The hot weather connection is that marginal electrical connections may act up in heat because electrical resistance increases with temperature.

Another possibility many have reported as causing seemingly unrelated symptoms to occur together is a failing ignition switch.