Its a fuel pacer or fuel miser, dont remember which, it makes the turnsignal lights on the fender light up when you give it to much throttle when cruising down the road. It works off engine vacuum. Low vacuum (like foot to the floor going up a steep grade) lights up.
Would my 74 Spacer (318,4spd) have a Miser set-up as well,...I have heard that the left t/sig light on the fender would flash or light up when It was time to shift (when the government thought I should shift) ...