Some motors have a kill switch (man overboard switch) -- red button, typically, with a clip and lanyard. Your '85 MAY have a kill switch in the tiller handle, at the end. It's probably meant to be depressed to stop the motor (shorts the ignition). In the case of a button, the circuit is open unless you press the button, shorting the ignition. If it fails with the circuit closed, the motor will not fire.
If you have the push button, you might try spraying it with a little wd-40 and operating it just in case it's sticking -- try to free it up. If the button/switch is defective, it would have to be disassembled. One of the leads usually goes to the power pack, and another to a mounting bolt for one of the coils (ground point). There may be a single line connector at the rear of the powerhead for the wire leading to the power pack. Disconnecting the wire would defeat the kill switch, if it's a problem.
Someone who has your particular motor might jump in here with added info. and advice.
