The test light is used to locate each wire needed from the wiring harness of the car (i.e. - which wire is hot with the key , which wire is hot for the dimmer , etc.) . You can use the diagram in the How-To's (that show the rear of the clock) to tell where each wire hooks to the clock .
A test light is pretty cheap & available most anywhere . It looks like a pointy screwdriver with a wire hanging out the handle (and a clip at the end of the wire) . You ground the wire (clip) and poke at the connectors you're thinking about tapping into & when the handle lights up when you want it to (like when the lights are turned on) , you've found your wire
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~~~~~~~~~~~~~~~Allen
