The '79 has a much different glow plug system. The relay is in front of the instrument cluster (firewall side). The fuse is in a small mounted fuseholder at the top of the firewall directly behind the engine. To find the fuse holder, just follow the wire from the rear glow plug to the firewall and there will be your fuse.

Visually check the fuse first, then use an ohmmeter to check for continuity from the wire from the fuseholder to ground. If you have continuity check for power to the other side of the fuse when you turn on the ignition. If you don't have continuity, start working through the glow plugs to find the problem. There are insulators on each glow plug which if not installed correctly will short past one or more plugs. These four plugs are all in series. Now that I've said that if the insulators are not on correctly, you can have continuity but have inoperative glow plugs. You will have to reason your way through this simple circuit and see that nothing is shorted around the plugs to ground.


Good luck,