I replaced the burned out license plate light on my 95 E320, but the dash indicator still indicates a fault. Playing around with this, I find the dash light goes away when I open the trunk, regardless of whether the license plate lights are on or not, but the indicator light lights up when the trunk is slammed shut. So there's something about the trunk closing that has to do with the dash indicator. Where can the problem be?

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95 E320 Cabriolet, 169K