I have an early '07 that I bought this past fall, auto dimming mirror didn't work (light didn't/wont' come on)

I probably haven't put 500 miles on the truck since I got it, waiting for spring/summer to come and get some use.

Anyways, 2nd to the last time I had the truck out I noticed the light was finally on. Than the next time, nothing?

I've un-plugged it a few times and what not, seeing it came on once it's obviously not completely dead? Any suggestions or is this a common thing?

Thanks.