Tried replacing the cluster bulbs with T10 because my cluster is really really dim, but they're not working, even with rheostat connected. The LEDs work fine as battery tested them. I have suspicions that someone back in JDM-land tampered with the rheostat, but one begs to question why?? I have a replacement rheostat which as 3 wires and (ordered from a UK eBay seller) but my "stock" one only has 2 wires. I guess they somehow combined 3 wires to 2...
And the retarted thing is that my dimmer switch works counter clockwise (dimmer as you turn clockwise).
So without further ado, HELP!!

Did you try switching the leds around? Iirc they only work one way.

Yes, LED's are polarity conscious.  Also you'll need to have the dimmer turned to maximum - or remove it and simply connect the two wires together.

Have them the wrong way around bro,
turn them 180 degrees,
if not you may have harmed them putting a straight car battery to them? Maybe,

Also, your other issue is your rehostat upside down and the knob on the wrong way? perhaps.

Dont know, should be easy to check if power is going use a test light?

Yep had a play around a bit more and indeed they are polarity conscious. Removed the little white variable resistor now all is working fine! Seems to have unlocked the power since LEDs apparently have a threshold voltage?
Such a minor mod with a big reward :)

Right on both counts - Merry Christmas!