After logic board replacement, no brightness control, stuck at max

I replaced the 2.4 GHz logic board in a late 2008 MBP due to a liquid spill. I replaced it with the 2.53 GHz logic board, due to the part being available and for a low price.

I replaced the board and it powered up just fine (after the spill it wouldn't power up at all.) While the thermal paste was breaking it I got a few sparklies on the screen and a few screen flashes / flickers. I continued to break in the thermal paste with a few more short term usages.

Now it seems to be running fine with one exception. I have no screen brightness control. The ambient light sensor works, in that it dims the keyboard backlight accordingly, but doesn't dim the screen. Further troubleshooting shows that the display won't dim by the F1 & F2 keys or the System Preferences>Display Settings either. The display sleep setting doesn't work either.

So it seems the computer has no control over the screen brightness. Is this a cable I missed (I followed the ifixit guide very closely) or is there some difference between the 2.4 GHz logic board and the 2.53 GHz logic board.

Thanks for your input.