Reading ohsofly's thread reminded me...
Why does the full lamp NOT illuminate for brake & signal? There are double filament bulbs in all sockets,and all bulbs are fine. I have never seen another blazer on the road w/o full lens-load! But I was behind a Suburban of the same vintage yesterday & that unit displayed the same problem! Any ideas?

 

Both bulbss should illuminate for brake & turn on your truck, but only one filament in each bulb. The tail lights on the fullsize trucks do not operate in that manner though.

 

Hey! Appreciate the info,lamps were in the unit when I bought it, so will do that this weekend.