Turn Signal Light Slow Flashing

While driving my 1972 Dodge Dart Swinger home Friday night, I noticed the left turn flashing slow in blinking. When I arrived home did some testing, with headlights off left and right turn flashers work as normal. When headlights on right works as normal but left is slow. When air conditioning is on the left will only flash once, maybe twice then not at all. Bad Instrument Cluster Voltage Requlator?