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Discussion Starter #1
I am in need of assistance from any knowledgeable electrical types. :)

This is regarding the white and green wire that sends an output voltage from the rheostat to the instrument lighting. When the rheostat is full off and lights are full dim, it's sending out 12v. When it's full on, lights full bright, it's sending out 0v.

My problem is, I got some new gauges a while back, and they each have a wire to connect to the vehicle's instrument lighting wire. Unfortunately, the gauge's dimming feature operates the complete opposite from how our vehicle does (12v = full bright gauges, 0v = full dim gauges).

Does anyone know of a way I can reverse the voltage coming out of the rheostat wire to these gauge wires? (i.e. 12v -> 0v, 0v -> 12v). Or is there a different solution to this anyone can think of? (I know I could just hook the gauge wires up to a constant 12v and call it a day at full bright, but I want the functionality if it's possible).
 

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Discussion Starter #2
Btw, found Thunderbox had the same problem with his Defi gauges here: http://spyderchat.com/forums/showthread.php?17409-dimming-the-gauges-in-gauge-pod-(rheostat)&p=258896&viewfull=1#post258896 Blitzo's advice to him makes no sense to me. I know our rheostat is biased ground, but the gauges want a source that is biased power. Don't understand what he meant by the last bit though.

For the record, my two gauges are AEM. This wire I am speaking of is not the main power wire, there are two separate power wires that go to constant 12v already. This is a third wire specifically for connecting to instrument lights for variable voltage.
 

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I ran into that gauge illumination issue and couldn't believe they'd do it that way... vary the "ground" side voltage. Anyway, if you look in the wiring diagram, you'll see where the rheostat is connected to a transistor. You would have to take that transistor output that's the opposite of what you want and feed it to another transistor. I can't remember doodly squat from my transistor days other than emitter-, collector-, and base- coupled (pick one) and of course establishing the bias. It can be done. You might be able to modify the gauges instead. Maybe ask the company.
 

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So far what I've read, they are talking about hooking the Light Buld Wires From the Hot ( 12 Volts ) and the Rheostat ( Dimmer Wiper ).. Not Ground and Dimmer Wiper.. that will get the 'Reversal' of the Dimming Feature..

They are also talking about hooking into the Radio Lighting Circuit.. But again, the Voltage looks to be Set up from 12V Hot to the Dimmer Wire.. Not Dimmer Wire to Ground..


So far that is all I've Gathered..


Cap
 

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Discussion Starter #5 (Edited)

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They are talking about an Inverter.. .. What Kevin was talking about.

Can't you just hook the Light from +12 to the Dim Line?..

What you you doing up this Early..

Cap
 

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Discussion Starter #7
They are talking about an Inverter.. .. What Kevin was talking about.

Can't you just hook the Light from +12 to the Dim Line?..

What you you doing up this Early..

Cap
I'm not sure sure what you mean hook the light from +12 to the dim line?

The gauge has several power wires. Two red that go to constant 12v, a pink that goes to switched 12v, and a grey, which is supposed to go to instrument lighting (0-12v variable voltage).

So, I connected that grey wire to the MR2's white-green wire that comes from the rheostat and carries 0-12v to the radio/instrument lights/etc. The problem is that the MR2's grounding system is opposite of what the gauge expects. I'm explaining this because I'm not sure if you understand what I meant?

I'm up because I'm on night shift again now. ;)
 

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I thought you said ( Implied ) that the Wires to the Light Bulb were separate from the 'Rest of the Gauge' and therefore could be hooked to the Dimming Wire Separately.. If that is the Case, then just hook the Lamp Wires to the Switched 12 volt line, and the Green Rheostat line..

If the Bulb Wires are not Separate, then You must use the 'Inverter'..

All Sounds Like a Real PITA.. For a Gauge!..

Cap
 

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Discussion Starter #11
Bulb wires aren't separate, if I am understanding what you mean. Seems like the only options are make this inverter thing or take apart gauge and change it internally.

Opening the gauge is way beyond my comfort and electrical knowledge level. Making the inverter thing I may be able to do, though as said, it looks to be a huge PITA. Then again, I wouldn't be happy just connecting the gauge to switched 12v so it's always full bright. I have an appreciation for appropriately set "cockpit lighting" that doesn't blind your night time vision.

Seems like I am left with only one choice, I hate soldering.... <_<
 

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Discussion Starter #12

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Discussion Starter #14
I bought the parts listed in the Subie DIY from Radio Shack today. $3 and change...and they were surprisingly easy to find. Now to see if I can hack this thing together without messing it up.
 

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Discussion Starter #15
Ok, I'm down to post #14-16 in the Subie thread (http://www.scoobymods.com/dim_omori_elect_gauges-t3115.html?t=3115 ) and I'm a bit unsure of what their intention was.

skivvie writes: "The Violet wire is the cars Illumination (+) and the Orange wire is the cars Illumination (-).
Connect the Illum. (+) coming from pin 7 to the Violet wire, and the Illum. (-) coming from the resistor on pin 2 to the Orange wire. "

So, what I'm wondering is, what is he referring to as the illumination + and the illumination -? In his example, there are only 2 wires in the Subaru dimming circuit.

In our car, there are a few different choices here. You have the rheostat that has a green 12v wire, a brown ground wire, and the white and green 0-12v wire.
Then, going into all the lighting (instrument panel, radio, etc.) you have 2 wires. The same green 12v wire and the same white and green 0-12v wire.

So I'm trying to figure out which of our wires would equate to what he is calling the illumination + and illumination -. Any thoughts?
 

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Discussion Starter #16 (Edited)
I *think* maybe I found the answer? Not sure if it's right though.

http://forums.nasioc.com/forums/showpost.php?p=3720279&postcount=46

"And to make sure I understand -

Illum + in the schematic is the wire that has 12V+ when my lights are on.

Illum - in the schematic is the wire that varies based on the dimmer from 0V (brightest) to 12V (dash lights off)."
 

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Here's what I posted on mr2roc.org last year:

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.
Well whadda ya know? I forgot about the (alleged) orange wire in head unit for illumination.
 

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Discussion Starter #18
Well whadda ya know? I forgot about the (alleged) orange wire in head unit for illumination.
Not sure what orange wire you refer to. I checked the back of the OEM head unit and there is no orange wire. It also wouldn't make sense to have two different 0-12v variable wires going to the head unit, since the white and green one from the rheostat already goes there.

I finally got my issue resolved. I put the inverter together, it wasn't too intensive, but was a PITA because I was working with tiny parts with my big ass soldering iron and soldering all the little terminals together was like balancing on a trapeez wire. Btw, I used the wires going into the radio head unit, the illum + is the green lighting power wire and the illum - is the white-green variable voltage wire.

Sure enough, it worked as advertised, the output wire from the inverter gave a full 12v when the rheostat was turned to full bright and voltage decreased when I turned the rheostat down (verified by my test light), which is exactly what I needed.

Unfortunately, I'm a bit disappointed with the outcome when I connected this wire to the gauges. It seems that my inverter is not going to 0v when the rheostat is turned down, but instead is putting out something some voltage still (maybe 5v, I didn't bother to hook up the multimeter and measure the exact output). The outcome is that when my instrument lights are turned off the gauge lights are full dim, when I turn the instrument lights on the gauges brighten up, and when I turn the rheostat from full off to full bright there isn't a very noticeable increase in brightness on the gauges. It's oddly almost indistinguishable between the two positions. I'm tired of messing with it all and it works, plus the part where it brightens when the instrument lights come on is kinda functional, so I'm just gonna leave it as is.
 
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