I'm helping a friend install a DB Digital Air/Fuel Gauge and I'm wondering what we should use for a signal to dim the lights. It says to use a wire that supplies power to the headlights, and that if one with a rheostat is used it will cause the gauge to malfunction.

I figure I'll hit up the power windows for switched power, but I'm not sure what to use for the headlight signal.

It's a '91.

 

IIRC is there not a separate 12V wire for the backlight? It has been awhile since I installed mine. If so, then run the dimmer signal to that and the switched one to the power wire. If not, then use the switched only. If it still has that gay smoked colored lens like mine, then you will want it at full brightness anyway.

 

if any voltage goes to the illumination wire, the gauge dims. I plugged in an "add a circuit" from the headlight fuse by your feet.

 

On a '91, at the back of the radio look for a red/black wire. This is the backlight illumination for the radio, and is non-dimmed. It has +12 any time the parking lights or headlights are switched on.

 

I'll dig for the wire behind the stereo if I have to but we're mounting the gauge in the A-pillar, is there a wire we can use somewhere under the dash that would be a little handier?

 

You can use one of the wires that comes off the rheostat, just don't use the variable one. Pop the switch out of the dash and use your multimeter while you work the rheostat dial to find the wire that's a constant +12V when the lights are on. If I recall, I managed to push the pin out of the connector a little bit, and I just sandwiched the gauge dimmer wire back into the connector alongside the pin and taped the wire up nice and secure. It was lazy as hell of me to not solder it, but it's still working fine and it's not like that wire will cause any real problems should it come loose.

It doesn't dim as much as I'd like though, as it's still fairly bright in nighttime use on unlit roads. I've got the blue gauge. The red one probably wouldn't seem as bright.

 

Depending on where you want to do your splices there is also a wire in the ECU harness which is 12 volts only when the parking lights are on. No idea why Mazda wanted that signal going to the ECU, but it does.

 

you said you were mounting it on the a-pillar, but just incase anyone is reading this and is mounting it under the radio where i put mine...the little light that is in the middle of our console, right behind the shifter, comes on when our lights are turned on and i just tapped into that. Works great so far.

 

Yeah, you can grab it at the instrument cluster. Red/black wire at position 2H on the back of the gauge assembly.

Also, you can take it from the back of the dimmer ****, same red/black wire goes there.

Pretty much anything in the interior that is backlit when the lights are on will have a red/black wire and a red wire going to it. The red/black is the switched +12, the red is the variable closure to ground through the dimmer ****. FYI- they're not using a rheostat, it's PWMed.

 

I use that for my guages (remember, this is for a friends car), and it's great I've got analog gauges and I run the backlight off that ashtray light so they dim with the dash lights. Perfect!