It could be that the Relay is defective. I would take it back.

Also when I tested a single Glow Plug connected to an automotive dash type Amp Meter connected to a batter; it pegged the meter at 60 amps (as hig as the meter would go) and as it got yellow read went down to about 16 amps.
So you will not be pulling 80 amps for 3 minutes on your way to work.

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84 300D, 82 Volvo 244Gl Diesel