Altitude compensation solenoid, alters injection timing by changing pressure on one side of the big advance piston in the bottom of the pump case depending on whether it is energized or not. Idea is to advance timing to compensate for less dense air charge and corresponding reduction in cylinder pressure at higher altitudes. This was one of the features that was introduced midway through 1984 model year; 200 and 700 series up through MY84 did not have it, the "1984.5" versions of both 200 and 700 were the first to get it, and 1985-onward all had it.
When powered with +12V, injection timing is normal. When disconnected from voltage source, timing is advanced by a few degrees. Solenoid operation is controlled by a barometric pressure sensing switch, mounted on the drivers side strut tower next to the GP relay, shaped like a little silver tuna can with two blue wires w/female spade terminals connected to it, which is designed to be closed (solenoid powered) at low altitudes and open at altitudes above ~3300'. When the engine is running, you can hear an audible difference in injection timing when the wire terminal is removed and reattached to the solenoid or the switch.
Should have +12V at that wire (and hear a click from the solenoid when wire is disconnected/connected) at most altitudes if system is working correctly, but in Reno, you might be above the barometric switch's threshold. It's a nice feature to have, but the troublesome issue with it is that its operation is based on the idea that your static timing will be set at the book value of .85mm, and a more advanced setting than that could result in excessive overall advance when the compensation system switches to high-altitude mode. Because I do run a more advanced base timing setting, like most owners here do, I disable this system by installing a jumper between the connectors at the switch on the strut tower, ensuring +12V to the solenoid at all times. In any case where this is true, or exact static timing setting is not known, I'd recommend this route, to avoid possibility of undesired excessive advance and resulting detrimental effects...
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