The place to start is by removing the starter relay, then we'll take some voltage readings in the socket, with a test light. You can use a digital voltmeter too, but a test light is more accurate for these tests.
The wiring diagram shows there's at least seven terminals in the socket. Two of them, terminals 3 and 4, are for the cruise control, and it's not clear if there should be voltage on them. Start by testing for voltage on every terminal with the ignition switch turned off. I expect you'll find 0 volts on each one. Next, turn the ignition switch to the "run" position, then check every terminal again. You should find 12 volts on one terminal. If you do not, check for a blown 10-amp fuse, # 18, in the fuse box behind the dash, to the left of the steering column.
If you do find that 12 volts, have a helper turn the ignition switch to the "crank" position, then test every terminal again. You should still have 12 volts on that first terminal, and now on a second one. If the second one is missing, check the 40-amp fuse link "E" in the under-hood fuse box on the right inner fender.
If both of those voltages are there, turn the ignition switch off, then move the test light's ground clip to the battery's positive post. We'll be testing for ground circuits next. Disregard the two terminals where you found 12 volts. Probe the rest of them. The test light should light up on two of the remaining terminals. Test those two again after you shift to "reverse" or "drive". You should see the test light turn off for one of those terminals. That shows the neutral safety switch is working.
Let me know what you find on those four terminals. Hopefully one of them will be wrong.
Monday, April 24th, 2017 AT 9:50 PM