Are you sure you listed the right engine size? Which model do you have, the LXI, LX, or JX? Do you have automatic heater controls or manual? Do you know if the radio uses a separate amplifier in the rear? Did all these things act up at the same time?
The only thing I can find that these have in common is the heater fan relay and the rear defogger switch share a ground connection. We'll have to pick one circuit to start with. The heater fan will be the easiest. Look for the fan relay in the inside fuse box on the left side of the dash. You'll need a test light. Digital voltmeter will work too, but the light is faster. Pull that relay out, then check for voltages on the terminals in the socket. Be careful to not stick the probe in so hard that it stretches the terminals.
One terminal should have 12 volts all the time. A second one should have 12 volts only when the ignition switch is turned on.
Move the test light's ground clip to the battery's positive post, then check the other two terminals. The light should be bright on one of them indicating a good ground. The last terminal depends on the type of fan speed control your system uses. If you have manual controls, the test light should change brightness depending on the speed you select.
That splits that circuit into four parts. Hopefully one of those tests will be wrong, then we'll know where to go next. I'll be back in two days, or sooner, to see how you're doing.
Sunday, December 6th, 2015 AT 12:19 AM