I don't know much about the dash in your '91 - but just to throw out some more suggestions - when I was doing the wiring on my '81 on the dash, I found out that the silly inst. cluster uses some diodes that control a sensor light along with the charge light in one voltage direction, and just the charge light in the other voltage direction (diode control). But for some crazy reason when the check light from my 3RZ ecu would ground out the circuit, both the sensor light (that I am using as my check engine lamp [MIL]) and the charge light would come on. It took me a while and I eventually gave up and jabbed my sodering iron straight through it and killed it. Now the circuits are completely seperated and my lights work great.
All I could surmise is that the sensor light is connected to the "poor mans ecu" '81 carburated emissions control ecu, and if the sensor light comes on then so does the charge, but of course if you are just having a charging prob them just that light would come on, but when I had it wired up, for some reason
BOTH VOLTAGE DIRECTIONS were causing both lights to come on some how.
it was like a voltage leak in the dash or something??
Good luck-
