Red transmission light is flashing, only has first and reverse

The transmission lower drivers left side red transmission light is flashing. It has only first and reverse. I drove down the road and manually shifted from first, second, third and fourth gears. It would not shift out of first gear. The transmission was low when I bought it in good to plus condition for $750.00 a local vehicle since new in Atlanta. This vehicle has very little sign of being molested or wrecked. I did notice the left of transmission over the left exhaust pipe to a large broken 6-8 wire harness bundle clamp allowing the 6 to 8 or so wiring bundle fall down closer to the exhaust pipe and the plastic wire bundle wrapping has separated over the exhaust pipe, but I did not see any burnt wires so far without testing the conductivity on both sides of the wires in that bundle which heads on up to the left finder well electronics components. OME fuses relays and terminals ends have no sign of bad and melted connections. Engine compartment hoses wiring and mechanical linkage looks good. I do not think this trooper has ever been off the road much. The transmission service history is unknown and the oil looks and smells okay, but I am sure it needs servicing. Can a code be read for faults? The consensus is it needs an electronic shift solenoid and there could be several. Any ideas for me to look for and test any and replace suspect components? Thanks for your time and help suggestions. The dealers may answer the phone with no help, tow it in for a few days. Yeah okay, I am a competent mechanic for more than fifty years. Tom, Atlanta