Nothing wrong w/ having the fan come on whenever the ignition is on, if you're in a pinch. Better than the engine overheating.

You say it eventually gets to ~45%, is that with the fan wired to run all the time? If so, the temp. gauge seems to be working, that might be an accurate reading.

I don't know about the LAF or any possible connection to the shift light.

You tested the thermostat, so that it opens and closes at the right temps., so that should rule out the thermostat being stuck open.
The fan not coming on by itself may in fact be the thermoswitch, but that wouldn't explain the temp. gauge not going above 1/2 no matter how long the engine idles, etc. You'd think it would have to be the gauge or it's sending unit, but maybe the engine just isn't getting that hot - is your distributor by chance tilted all the way towards the firewall in the engine bay? If so your timing is retarded, which may be the issue. Regardless though, if you have access to a timing light it might be a good idea to check it.