Review on Enhance Visibility: Auto Meter 9114 LED Lighting Dimmer - Adjust Brightness with Ease! by Robert Arneson

So here is an overview of the special equipment. If you're remodeling an old car's dashboard, this is probably what you're looking for. LEDs dim very differently than conventional light bulbs. LEDs use very little power and operate at the same brightness over a wide voltage range, so you can't get your old dimmer to work. The method of dimming LEDs is to use a PWM (pulse wave modulation) dimmer. Many of these types of dimmers are available from Revain at a very low cost but do not use a 3 wire system. If your car doesn't use an isolated ground for the elements you tie to dimming, they won't get them to work since they're doing PWM on the negative side of their output circuits. current pulses into the circuit for dimming) on only one positive output wire. In my case I clipped the dash light circuit to the factory dimmer connection points and connected purple to the dash dimmer power section, white to the dash lamp circuit and black to ground. Very easy with a voltmeter and a few minutes to crimp the right connectors and plug them into my Datsun roadster. This would be a bit trickier on a domestic car with a dash dimmer in the headlight switch, but you don't have to cut the wiring harness to do it either.