When I tested several Glow Plugs one at a time with a 60 amp automotive dashboard type Amp Meter I found that that they would peg the gauge at 60 amps for around 1.5 seconds then as the plug got red hot would go down to 16 amps and stay at 16 amps. This was on my 84 300D. The test was done on new Bosch Glow Plugs.

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84 300D, 82 Volvo 244Gl Diesel