This is a very simple modification, but it has many steps.  There is already a very detailed writeup on the web, so I feel it would be pointless for me to basically repeat that.  Instead, follow this link:
http://montecarloss.com/Dash_Lights.html

I will add the following tips:
Watch the weatherstrip on the vent and blocking out the light from the blinkers, it rips easily. 
Make sure you go slowly!  The screws are small and they strip easily!  Also, try to use a magnetic screw driver because you don't want to lose any of the screws and be blessed with a nice rattle.
I ended up replacing them with new 168 bulbs.  They are nice and bright, but I still have to keep them turned up all the way.  This could also be causes by an old headlight/dimmer switch.  If I did it again, I would probably step up to the 2825 bulbs.  Can't be too bright :)  I only replaced the easy ones to get to.  However, I did take the extra step to remove the whole cluster from the car to clean the contacts with an eraser and paint the backside w/ silver paint.
Also, don't forget to replace the bulb behind the heater control, otherwise when you dim your dash you won't be able to see the heater settings.

Well I think thats it, hope this helps you see your gauges at night again!
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