Some of the trucks are wired differently than others, but they all use the same color wires. Light blue and dark blue.
Looking at your cluster plug, do you see the two wires. The pins on the plug are numbered and the wires go on pins 10 and 11 for light clusters and 9 and 10 for gauge clusters. Notice the pins are numbered 1 thru 12.
See the diagram below and notice the light cluster pins in the middle of the diagram and the gauge cluster up at the top of the diagram.
If you still have the cluster out, you can use a 12 volt source and ground the cluster tin to check the bulbs to be sure they work. I usually use my truck battery on the bench. Get a couple of jumper wires with alligator clips on each end and ground one to the negative terminal then clip the other end to the cluster metal housing. I use black wire for negative and red for positive.
Now clip the red wire to the battery positive post then touch the other end to the number 10 and then to the number 11 pins for light clusters, and 9 and 10 for gauge clusters. Watch for the bulbs to light. If they do then the cluster is good. If not then your problem is in the cluster, a bad bulb or bulb ground, or the copper strip is broken. If both lights are out I doubt the strip is broken, Unless both strips are broken.
Be careful with live voltage as you could damage a gauge.
If you have a multimeter you can check for continuity on the strips between the pin and the bulb mount connection then check between the cluster housing and the bulb ground.
If you get the bulbs to work in the cluster but they still don't work then you need to look at the half moon connector on the steering column and see if the two wires are there. There should be four wires, two on each connection. One light blue wire runs up to the turn signal switch and one runs up to the cluster plug. The same for the dark blue wires.
If you only see one set of wires on the connector, the other two wires may be joined at the inside of the cab junction block behind the fuse panel. The firewall connector in the engine compartment will have one light blue and one dark blue wire for the left and right turns. They have to be there since you said they work.
Hope this helps. VV