I bought a '91 S-10 Blazer almost 7 years ago now from a good friend and it still runs great. Each year I have to pass state inspection which is usually no problem... The speedometer has not worked since I have had the vehicle. I tried to fix it but could not find any problems when the dash was apart...anyway, not this instructable. While the speedometer is not necessary, the blinker indicators are and since they are on the same display they are also not working. I mention the speedometer because that is what everyone thinks is important but in reality the state of Texas cares more about the blinker indicators... This was done to pass the second inspection I had... Oddly the first one missed it... That was in 2007 so over 5 years have passed with this as my daily driver and I have made no adjustments.
I found a schematic online for the signal wires and used a multimeter to test the lines.
The LEDs were purchased as I had none in my pile-o-stuff that could handle 12 volts.
The wire was some extra speaker wire, used in the past but too small to be of any use now.
Wire nuts were laying around.
Of course, duct tape was used.
The schematics I found online were lacking but seemed to indicate that most of Chevrolet's similar vehicles were using light- and dark- blue wires for the turn signals during this time.
I took a multimeter reading voltage and cut the dark blue wire and touched the negative multimeter lead to the chassis and the positive lead to the wire. It showed 12 or so volts (it has been 5 years) and the light blue wire did the same when the turn signal was activated in the appropriate direction.
As a picture shows, one end of the speaker wire was attached to each of the cut wires and then attached to their own positive lead (long leg) of the left and right LED. The negative leads of the LEDs were attached to wires attached to the chassis. Then I just taped in the lights and reinstalled the dash covers.
Here is a video of the blinkers in operation.