I have worked primarily on 240's but I would suspect that the wiring circuit and harness is similar to my 89 240. My first guess is that the cleaning of the starter wiring broke the blue yellow wire leading to the solenoid (terminal 50) within the harness. You can isolate the location of the break/short by tracing back from the solenoid to the ignition switch. First disconnect the solenoid lead (blue yellow wire) and attach a voltmeter to see if 12v is or isn't present when you turn the ignition to position III(just to make sure there isn't a short somewhere). Given your symptoms 12v should not be present. Next, look for a large gray rectangular plug as part of the wiring harness on the engine firewall just below the middle of the windshield (should be near the oil and transmission dipstick). This plug connects the portion of the engine harness that leads to the fuel injection and the starter solenoid. Immediately next to this larger plug should be a spare lead with a black plug that one could plug another lead into; it should have a blue wire coming into it (from terminal 50 of the ignition switch and a yellow blue wire that goes to the starter solenoid). This plug is a remote start access point; by running a lead from the + terminal of the battery you should be able to start the car. So you can either check the continuity from this plug with the lead that plugs into the solenoid (be sure to lead it unplugged at the solenoid) or apply 12v to (with the solenoid lead plugged in) it to see if the starter engages. If continuity is not present then the wire is broken within the harness. You should also check to see that this lead is indeed receiving 12v from the ignition switch by connect the voltmeter, turning the ignition switch to position III (12v should register only in the III position and not the II). If you find that these contions are present then you have found the problem. You can then run a wire from the remote start access plug to the starter solenoid terminal 50 as a fix without having to replace the whole wiring harness.

If however, continuity is present and 12v at the remote start access plug is not present you will have to trace back to the ignition switch. If you already located your automatic interupt switch, I would use the voltmeter at this point to see if 12v is coming out of the ignition switch. You can work back from this switch to another connector in the engine compartment (should be on the right had side of the driver compartment next the to heater fan) that has two blue wires (one from terminal 50 of the ignition switch and the other goes to the remote start access plug in the engine compartment) and a blue yellow that goes to terminal 30 of theJetronic unit). It is also distinguished by a black "loop" wire that plugs into the top of the connector. If you do not get 12v at this point when turning the ignition switch on to position III, I would then remove the ignition switch and test the terminals.

Hope this helps.