The first thing that comes to mind is the ground wire. The middle screw that holds the gauge cluster to the dash is supposed to ground the gauges to the body of the dash with a single uncoated hard wire. Even if yours is in place its a good idea to install a second ground wire from the back of the gauges to a known good ground, that should get the turn signals working.
The power for the dash lights comes from the headlamp switch and is controlled by turning the knob left or right to brighten or dim the lights. These switches have always been troublesome and most parts stores still stock them or can at least order them in. To remove the switch you must first remove the knob by pushing a button on the side of the switch and pulling out on the knob. It will pull out the middle shaft of the switch and turn the headlamps on in the process so you may want to disconnect the battery. If I remember correctly the headlamp switch also needs to ground to the dash in order to turn on the interior lights.
It is also a good idea to just replace all of the bulbs in the gauges. Parts stores sell 194 bulbs single or in boxes.
Please post what you find out. Neill