Hi all, ive bought some aftermarket gauges for water temp and oil pressure. Theyre relatively cheap gauges (ebay specials-dragon gauges) and only have 3 wires...+, - and sensor wire. I would like to wire them up to be dimmable, and hooking up a dimmer switch to the + is simple enough, but since the illumination for the gauge isnt on its own circuit/wire...im thinking that if i just put the dimmer switch on the + wire, it will affect how the gauge reads because its not getting the correct current/resistance? Can someone please confirm this for me?

I really dont want to break open a new gauge and start hacking at wires to be able to dim the lighting...but if thats all that can be done to dim them, then i will have to do it

 

well...after a few whiskys and 2.5 hours after my initial post, i decided to tackle it myself. did the math and figured that without having the illumination on its own circuit, altering the voltage to the whole gauge through the red wire would wreak havoc....after opening the gauge its clear that the illumination does infact, take its power from the gauge input...













SO!, there you have it...if anyone else wants their cheap ebay gauges to have illumination dimming capabilities, this is how to go about it. i know there are 4 white wires on the back of the circuit board, but tracing them to their source is pretty straight forward---doing that, combined with following the circuits within the board will show what's, what.

all thats needed after the wire is cut and extended, is one of these cheap funky little dimmers
http://www.ebay.com.au/itm/DC-12V-8A...0AAOSwNNxWFU0d

Sure, u could wire it straight to the cluster dimmer switch, but they will be out of whack (the gauges will be alot brighter considering theyre led). Thats y ive opted for a secondary dimmer switch.

Edit: i had to break open the gauges again and repeat the above process for the negative wire on the illumination circuit aswell. Although the lights had their own power source, there was an issue with an inaccurate gauge reading (showed 5psi as soon as the gauge had power-no it wasnt residual pressure, the car hasnt been started for a month). So obviously the gauge is calibrated to allow for the resistance/current for the lighting circuit. There was also an issue with the dimmer switch i ordered which had +/- in and +/- out. When i used the earth from the gauges which was the common earth for all circuits, i adjusted the dimmer switch, and the lights would dim, but the gauge would also read from 0-40psi relative to the switch being turned up and down.

If there is a single wire, in line dimmer switch the simply works on the + wire this probably wouldnt have been an issue. But its all working properly now with the illumination having its own earth aswell.