skulls2rock, here is what the service manual has to say about the heated mirrors:"The operation of the heated mirror system can be
confirmed in one of the following manners:
1. Turn the ignition switch to the On position. While monitoring the instrument panel voltmeter, momentarily depress and release the heated mirror switch. When the heated mirror system is turned On,
a distinct voltmeter needle deflection should be noted.
2. Turn the ignition switch to the On position. Momentarily depress and release the heated mirror switch to turn the heated mirror system On. The heated mirror operation can be checked by feeling
the outside rear view mirror glass. A distinct difference in temperature between the unheated and heated mirror glass can be detected within three to four minutes of system operation.
The above checks will confirm system operation. Illumination of the heated mirror system indicator lamp means that there is electrical current available at the heated mirror relay, but does not confirm that
the electrical current is reaching the outside mirror heating grids.
If the heated mirror system does not operate, the problem should be isolated in the following manner:
(1) Confirm that the ignition switch is in the On position.
(2) Check the fuses in the Power Distribution Center (PDC) and in the Junction Block (JB). The fuses must be tight in their receptacles and all electrical connections must be secure. When the above steps have been completed and both outside mirror heating grids are still inoperative, one or more of the following is faulty:
² Heated mirror switch, electronic control logic and timer circuitry, and heated mirror relay.
² Heated mirror wire harness circuits or connectors.
² Outside mirror heating grid (both mirror grids would have to be faulty).
If turning On the heated mirror system produces a severe voltmeter deflection or fuse failures, check for a shorted circuit between the output of the heated mirror relay and the outside mirror heating grids."
It does appear that when only one mirror is not heating up, the fault is either in the wiring to that side or the heating grid itself. Review the attached wiring diagram and use an ohm meter to see if your grid has continuity. Of course you also want to check the issues that Richdave pointed out. Hope this helps, good luck.