1988LE Caravan dome light/left map light

On the LE with overhead map lights, one of the rear map lights serves double duty and lights up when either side door, or front doors opens. Mine does not light up with door opening anymore, but works fine if the push button is pressed. I have the service manual and noticed that there is a DIODE ASSEMBLY that may contain the logic to allow this dual personality. However, I cannot find this DIODE ASSEMBLY in the vechicle. Does anyone know where it is located?