Electrical Wiring help (factory dimmer knob)

Discussion in 'SN95 4.6L Mustang Tech' started by Seclusioned, Dec 24, 2012.

  1. Ok so I got my new white faced gauges that I bought off ebay. They came in an APC box and APC sticker. Anyways the included instructions says do not run off the power from the factory dimmer knob as it can destroy or mess up the gauge glow. It also says do not remove the stock overlay. I want to do away with the dimmer knob that came with it (see pictures) and run it to my factory dimmer knob. Or at least run it to the headlight switch so that the gauge lights come on when I turn my headlights on. If any other pics are needed or info please ask. But I want to know 2 things

    1. How to do away with the dimmer knob they sent and splice it into the factory lines, and if thats ok and will not mess anything up. (advice from someone who has done this with something similar would be helpful) I dont see the issue. Its still all coming from the same voltage and as long as I keep the converter box whats the issue? (not very electrical inclined here!)

    2. Why do they say do not remove the factory overlay? (IE the plastic piece for the gauges!)

    Here is what I bought

    In the pic you can see the power cords. the converter box, and the dimmer knob.

    Attached Files:

  2. re the electrical:

    The electroluminescent panels used in "indiglo" gauges requires a fairly high voltage to operate. In fact, not only is it high (on the order of 150V) but is it also alternating current (AC). That little blue box in your picture is a power supply (often called an "inverter") that generates the required AC voltage from the car's 12V DC supply using a switch-mode power supply circuit. (When you hear these supplies "humming" or "buzzing" you're hearing the switch-mode supply in operation; the sound comes from electrical parts like transformer cores moving ever so slightly in response to changing magnetic fields...)

    The supplied potentiometer is used to vary the amplitude of the AC voltage coming out of the inverter and operates on the inverter circuit directly. Without seeing a schematic of the circuit it's hard to say exactly what it's doing but I surmise it's operating on the feedback network of the switcher.

    Whatever the case, you can't just cut those wires and connect them to a totally different system (e.g. the dimmer output.)

    If you knew more about the circuit you might be able to design (or have designed) a little circuit that sniffs the car's dimmer voltage and generates a corresponding resistance across those two leads controlling the inverter using, say, a small bipolar transistor.

    It suffices to say do NOT connect those wires to the car's dimmer. You will break the inverter.

    re the OE gauge faces:

    Not sure but it may have something to do with damaging parts trying to get the old one off.
  3. Well that was informing lol. I will take your advice however I just wanted to use the factory dimmer knob instead of the one they used. Not do away with the inverter. Just the knob they sent. But either way I will take your advice and just tie the hot wire into something that only comes on when the key is turned over. I dont want to have that knob anywhere visible so I may find a spot under the dash to mount it to that is accessible by reaching under.
  4. Also the "destructions" says to "locate a power source, which is connected to your parking lights, and attach the red wire." But they say nothing about the ground... Glad I know better then that!