IP is OK, it's your ground.

Remove IP, and look at firewall, upper left through the hole in the dash.

You should see a bunch of brown ground wires. Clean those connections and see if it helps.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles