It sounds like you're looking at the ignition switch for the wrong thing. If the key is loose, that's in the lock cylinder. The switch is separate from that and can develop overheated contacts. In some years that switch was on the side of the steering column, under the dash. Start by looking at the connector body and the switch terminals for signs of blackened terminals or melted plastic. I can describe how to repair that but a new switch will be needed.
The switch contacts can also be pitted and arced with no external visible signs of overheating. Besides that switch, there can be a corroded connection, a stretched terminal in a connector, or a broken wire in the tilt wheel column. The fact you observed the radio will work when the heater isn't on points to the switch though. The high current the fan draws will overheat those contacts much faster and lead to an intermittent connection.
My preferred way to diagnose this type of intermittent problem is to fashion a number of test points where you can connect a voltmeter or test light to watch while you're driving. In this case I would go right to the ignition switch if the wires are accessible. If you have the service manual, you can use the wiring diagram to determine which wire goes to the accessory circuit. If you don't have the diagram, you can figure it out by seeing which wire has 12 volts when you turn the switch to the "run" position. There can be two or three of those but there's a good chance an '83 model will have just one. Attach a small clip lead, or poke a piece of wire into that terminal, then connect your test light to it. You'll see the test light light up, or the voltmeter will read around 12 volts when you have the ignition switch on. Now it's just a matter getting the fan and radio to quit. If the test light goes out too, the break in the circuit is before where it's connected. That would likely be in the ignition switch. If the test light stays on when the circuit quits, that proves the cause is after that point, typically at some other connector.
If the problem is after the switch, a good suspect is the fuse box. GM experimented with using aluminum wire around that time. They were attached to the fuse box terminals with brass rivets. Two different metals and an acid causes "galvanic action", similar to what takes place in a battery, but in this case it's corrosion. Road salt is an acid. If that gets on your shoes it will migrate through the carpet up to the fuse box where it leads to corroded and loose connections. Water alone will do that too. Aluminum oxidizes very quickly too, but that oxidation protects more oxidation from going deeper. When you scrape away the oxidation, you'll get very shiny metal that will also oxidize within a few seconds. Once that starts, and the powder flakes away, the wire under the rivet head becomes loose, then normal vibration rubs more of that oxidation away which allows still more to occur. If you let that go on long enough, you'll have just a pile of powder on the floor and no wire.
The way you can diagnose that type of bad connection is to find you still have 12 volts at the ignition switch when the circuit quits, but there won't be any voltage on either side of the radio fuse or the heater fan fuse.
Thursday, October 10th, 2013 AT 2:05 AM