You can do a rough estimate of the glow plugs' heating ability by measuring the resistance of each GP and compare to a known good one. The GP really needs to be removed, hooked to a battery and be made to glow (or not) to really test it.

I think Diesel Giant has a pictorial on testing the GP wiring. You should also check the fuse which may be located in the relay box. I don't know on your car.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.