A battery charger or a spare car battery will work.
Follow the light traces for the dash lights and see how they connect. apply 12v dc to the traces that connect the lights and they will light. Just don't hook the polarity up backwards, it won't hurt anything, but when you install the cluster into the dash none of the lights will light!:angry7:
These are also good for swapping out sidemarker lights, and other miniature lights! Great and easy mod to let your charging system catch it's breath!
