I've been digging for you, but haven't found a test procedure for the relays. I have a sneaking suspicion that in the shop, they're more likely to do a pull and plug type check than actually test the relay itself, but I could be wrong.

The starter circuit on the Turbo Diesel is battery direct to starter, starter to ground. The starter relay circuit is ignition to relay to starter to ground. As far as primary cranking power for the starter, there doesn't appear to be anything else on the circuit, but if you've lost power to the ignition circuit, the relay won't ever close to allow power to the starter motor. From the looks of it though, as the starter solenoid is integral to the starter chassis, you should be able to test for positive power at the starter terminal.

It really does not seem that there is a likely candidate for your problem other than the ignition circuit. Nothing else really covers the range of systems that you're seeing down. As you have no lights at all, I'm more convinced as to it being a break in this line somewhere downstream of the fusible link before the ignition circuit, but I could be wrong. I doubt it's on the ground side since your headlights ought to be fed to the same ground side as everything else. Headlights not dimming when you turn the key would indicate that there isn't even a start of a power drain, so a frozen starter or something of that nature's likely out.

The diagram shows the starter relay closer in the circuit to source (battery) than the ignition switch, but doesn't say whether that's one of the relays in your fuse box, or if it's actually at the starter itself. That may be an easier place to check for voltage.

See if any of this works and we'll go from there.

James