The battery -ve terminal is spring loaded on a quick release (well mine is, anyway). Unpop the clip and tap the -ve terminal down as far as it will go on the battery post before popping the clip closed again. If you don't lift it off, you won't have to reset the clock, radio etc. Don't do this with the engine running, by the way.
The terminal can seem a little loose due to the spring loaded nature, even when tight.
The only way to test a glow plug properly is to take them out one by one with a 9mm long reach socket and connect them across the battery. They can fail and light up half way down the side, like mine did in the pics earlier in the thread. You can't always pick this up with a multimeter or diagnostics.
If you find any duff ones, I wouldn't recommend buying Densos to replace them. I had 2 die within days of fitting.
Make something idiot proof and someone will only go and build a better idiot...