I know this has been done before but wanted to add a little more information that I had trouble finding when I went to replace the bulbs in the HVAC header. 3 of the 6 bulbs in mine were burnt out (20 year old disco, to be expected), AB has a set of them for $35 plus $4 shipping which I thought was absurd, and that's with a discount if you buy them all as a set! I replaced all of the bulbs with LED's from superbrightleds.com, ordering 6 of item NEO5-GHP, a 5mm green instrument bulb, grand total of 14.xx including shipping. Here's what the bulbs look like in comparison:

L:LCD back-light, C: Temp button and control button back-light, R: LED replacement

Removal of the header is easy enough and well covered elsewhere as is opening up the back of the header unit. Once that's done you are looking at this (4 bulbs in place, 2 sockets empty, note the silver pads on each side of the socket):


The problem (and really, it is the only real problem) is that LED's are polar, they care about which side is positive and negative, whereas the original bulbs are incandescent and they are non-polar, so you can plug them in anyway you want. Unfortunately the LED's themselves don't indicate which side is positive and which is negative. In addition there is no indication on the circuit board which side of the pad is positive and which is negative! The only way to determine the LED polarity is to get out your multi meter and do a continuity test on each one and then mark which side is positive/negative.

Now here is the part where my labor can hopefully save you some time...for each light bulb socket the left hand pad is positive EXCEPT the bottom center socket where the right hand pad is positive. Put the bulbs in place in the correct orientation, screw it back together and test in the truck (pro tip: plug in the wires but don't snap the unit back in, then test, so you don't have to remove the whole thing if you get one of the bulbs wrong). You have to hit the power button for the main LCD to turn on and turn on the headlights for the rest of them to come on.

Overall I'm pretty pleased but be forewarned, the LED bulbs that back the LCD screen cause it to be much brighter then the stock bulbs. I don't think that it's going to bother me (sort of an unintentional map light) but if it does I might have to figure out a way to "de-tune" the light output of the bulbs with a tiny resistor, tape, or marker.

 

I did that some time ago. LEDs where way to bright, I had to tune the brightness by putting some resistors in series. I ended up soldering the LEDs and resistors directly on the board. LEDs never die, they only get dimmer over time (I still have some working LEDs from the 1980s), so soldering is no disadvantage. I ordered the LEDs from superprightleds too, but buying just 10mm (fit that hole) LEDs would have been a lot cheaper (don't buy LEDs on ebay, spend a bit for quality from an electronics distributor like Mouser or Digikey, LEDs are very cheap).

 

Do you happen to remember how many Ohms those resistors are? Thanks for the tip about soldering right to the board, that might be they way I go if the brightness ends up bothering me.

 

I can't remember, it was several kOhms, since these LEDs are very efficient.

 

The problem I have with my climate control after I added blue LEDs is that it is too bright. It lights up the cab very well and the dimmer switch only does so much dimming.