S At the relay there is only 9.5 volts on the top post and 0 on the other three. There is also 9.5 volts at the 12 volt block right above the relay.
Dirty, test that point with a test light, not a meter. I suspect the light will not light.
Why?
If doghead is right (and he probably is), your fusible link has failed but there is a bit of residue that is partially conducting electricity along that path. Thus, you are seeing the 9.5 volts with the meter. Meters have a very high input resistance - they don't load a circuit at all. (Well, not enough to matter in automotive work.) If there is a very high resistance (like a corroded connection or a burned fusible link) between the battery and where you are measuring, the meter will measure the voltage, even sometimes full voltage, but put a load on that circuit and that high resistance will drop that voltage like a rock, and your test light will not light.
That's why it's always good to have a test light
AND a meter in your tool kit.
Try the test light and let us know what you get.
Also, I suggest you test the resistance of your glow plugs. If one is shorted, you'll blow that link in a heartbeat.