'73 240z, pulled out the tach to fiddle with it because it only worked when it wanted to, fixing it up went marvelously because all it needed was some sanding down of the copper contacts to remove oxidation. NOW, putting it back together I've got four holes in the back of the tach for two backlights and two turn signal lights, and lo and behold I've got two backlights and two turn signal lights in the dash harness to shove back in those holes.... AND ONE MORE! Now I've gotten out my mirror-on-a-stick, shoved my head in any holes I can fit it in, searched forums, the factory service manual, and a crusty old Haynes manual and I'm not getting anywhere on this. It has it's own ground wire unlike all the bulbs that ground to the tachometer's housing and have a single power wire, and uses a different kind of lightbulb (push in, instead of bayonet type). It turns on with all the standard dash backlights when I flip on the headlights or parking lights.

tach backlights and turn signals (one off-camera) on left and right, mystery light in bottom center. It has a light colored plastic hole-mount type socket, and a pair of black wires coming out of it to a connector with a black wire and a red wire with a blue stripe which go into the dash harness next to the turn signal/backlight/rheostat wires. There is a bullet splice in the black wire between the harness and the large plastic two-wire plug

regular dash lights use lefthand bulb, mystery light uses righthand bulb

Does it come on with the door switch or the light switch? I have one under the dash in my 73, called the ROOM L. on the wiring diagram, 2 wires, red/ blue and black, comes on with the door switches. I have not found where it mounts.

Comes on with the headlight switch. Can't comment on the door switch because nothing comes on with my door switch (working my way down the electrical gremlins in order of importance, dome light is kinda low compared to, say, windshield wipers) New development poking around, it seems to fit quite nicely in this odd little metal can with two... wire-like-objects? coming out of it that seem to go to the hazard switch and the cigarette lighter. Possibly some kinda light-piping to illuminate those two? The bulb mount clips into it nicely but neither the hazard switch or cigarette lighter SEEM to illuminate. Am I totally off base here?

(this picture is looking straight in the hole where the tach goes)

Edited December 16, 201113 yr by Captain_Zeros

YEP. It's a fiber optic thingy.

http://www.viczcar.com/forum/index.php/topic,8393.msg82116.html#msg82116

Cool, when I finally find a good three wire tach to replace my original, I will have to look into that bulb.

I just replaced my lights this past spring - mine is a 72 and did not see anything that looked like that in my dash

After some searching, apparently it's a '73 only thing. I hooked it all up and YEP fiber optics to light the hazard switch and cigarette lighter (a little dim to see in daylight though) Who knew my 70s car had fiber optics in it.