First I would connect a voltmeter to a GP, turn the key swirch to the position where the GP are turned on and see if the GP are turned on and then turned off after about 40 seconds. If they are first turned on and then turned off, GP relay is OK for this test.

Next I would turn key switch off and then and start the engine in the normal way and see if the GP are turned off when the engine starts (newer MB GP may stay on for a few seconds). If the GP are turned off, GP relay is OK for this test.

Next I would do a resistance test on the GP. You should have a digital ohmeter for this test. Pull the GP cable connector out of the GP relay. Connect one lead of the the ohmeter to engine and the other lead to one of the holes in the connector and measure resistance. It should be about 1/2 ohm. then measure the other GP the same way. If any GP reads different from the others, it should be replaced.

Replacing a bad GP may fix the indicator light on condition. The indicator is supposed to blink when an open GP is detected. Maybe your just stays on.

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