Illumination wire -- not rheostat controlled

[Digitalwave]

My new Innovate gauges so to not use an illumination cable that is controlled by the rheostat (variable headlight switch), as it would cause the gauge to malfunction. They suggest using a wire that just has power to it when the headlights are on. Does such a wire exist under the dash, or would I have to run something from the engine bay?

[Todd Black 88]

Why not the radio power wire?

[Digitalwave]

Radio power would work for 12v switched to power on the gauge. I am talking about the dimmer function of the gauge. The instructions say that a variable current wire won't be suitable, it either needs to be unpowered when the headlights are off (full brightness) or on when the headlights are on (dimmed).

[Gregs///M]

Radio power would work for 12v switched to power on the gauge. I am talking about the dimmer function of the gauge. The instructions say that a variable current wire won't be suitable, it either needs to be unpowered when the headlights are off (full brightness) or on when the headlights are on (dimmed).

You can find that wire at the headlight switch. 0 volts when no headlights, 12v+ when headlights are switched. its the same wire that triggers the headlight relays. Look in the ETM for wire colors or probe it in the switch yourself.

[e30evolution]

I would pull from parking lights

[Digitalwave]

Just to update this, the radio wiring harness illumination cable did not seem to be controlled by the rheostat when I tested it. The voltage was constant as you dimmed or brightened the interior lights from the switch panel. So, it worked for the illumination function on my gauges.

[george graves]

My new Innovate gauges so to not use an illumination cable that is controlled by the rheostat (variable headlight switch), as it would cause the gauge to malfunction. They suggest using a wire that just has power to it when the headlights are on. Does such a wire exist under the dash, or would I have to run something from the engine bay?

The parking light circuit is what they are referring to - available at the switch, since they can't do the correct input for a real illumination wire. And many people (including the "innovate e30") guys get caught up by the dash light circuit. It's a common issue. That's mistaking the dash light for ground (as it will seem to be 0 volts). Then you blow the dimmer, and maybe even the OBC and radio.