I'm putting a new radio in my '77.  It requires 2 sources of power, one constant 12 volts for the clock and one "accessories" which is on when the ignition in on.  The three-wire plug into the original radio has a black (ground), yellow (accessories), and a gray, which is not indicating any voltage.  Should that be the constant 12 volts?  If so, any help on why it is not hot.  If I have to get constant 12 volts from some other splice, please guide me to the proper wire (color) and where it is located.  Thanks!

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The gray wire is for the light inside the radio at night. Turn on your lights and check the wire for voltage after that. The cigar lighter/clock would have a constant 12 volts.

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The Gray should be for lights for the old radio. turn your headlight sw on and you should see 12 v then.

Hi Dan,  The color of the constant 12v wire to the cig lighter is Orange. If you choose to run a new wire from the battery positive terminal, I suggest that you use an inline fuse (10 amp)close to the battery connection. This fuse will protect the wire from meltdown should it short to ground.

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Joe T

I'll second Joe's comment - inline fuse close to battery is definitely a good thing.  A 12 ga wire directly connected between an almost infinite current source (e.g. a car battery) and ground will get very hot very quickly.  I have some small jumper wires for electronics (used them to bench test my clock) that have the insulation burned off and they were only inadvertently connected for a second or less!  

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I simply tapped into the cig/lighter (orange) wire.  This way, no need to run a wire under the carpet and no need for in-line fuse.

I found that the positive post on the clock is right there on the back of the instrument cluster.  I merely tapped into the 12v supply with a round connector and about 12 inches of wire with a lag connector to the wiring harness for the new radio.

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