Someone asked me how to connect their aftermarket gauge so it has variable illumination like the radio, combination meter, and a few other things. They said the stock head unit has an orange wire for this. I think that's an output of the head unit, but can't be sure. In the Taillight and Illumination page of the wiring diagram (that's page 5) it shows the rheostat in the lower right corner. That has two wires going to the combination meter. Inside the combination meter is a lamp marked Illumination and on either side of that are Green and White-Green wires. It looks to me like all the lamps in the car that have variable illumination get:
- 12V from this Green wire (as long as headlights and taillights are on)
- A voltage that varies from 0V (0V would give max brightness) to 12V (dimmed all the way) on a W-G wire
Question:
Say you have a lamp you wish to add but do not have a head unit. I don't know if that's the case with this other person or not, but it is with me. I know one way to control the brightness, which is to connect one side to this G wire and the other to the W-G wire, tapping off in any number of places (like the wires going to the head unit that you don't have). I'd prefer another way to do this... like a ground and another wire that has 12V on it (compared to ground) at max brightness and less than 12V (down to 0V) at lower brightness. Is there a place to tap off 0V = min brightness and 12V = max brightness? That way I could connect one side of my additional lamp to ground and simplify the wiring.
From looking at the circuits, you have understood the operation of the standard wiring perfectly and certainly the easiest is to just connect additional illumination between the Green and G/W wires. I can't see anywhere in the circuits where you could get the same effect connecting one side of your additional bulbs to ground. You'd have to make up an external circuit. Depending on how the rheostat operates, you could just connect a single transistor wired as an emitter follower direct to the output. Alternatively you would have to use an extra transistor as an inverter, in which case you could use the G/W wire to drive it. If you're happy to build something like that then I can supply a suitable circuit. Otherwise probably best to use the G/W wire and accept the additional wiring, although if the bulb in your aftermarket gauge is connected to the case (ground), this could be a bit tricky
That's what I suspected. Thanks for confirming that. I'll run an extra wire to my lamp.