Hello XXXXXXXXX, my name is Jeff.
The existing wiring that is coming to the old lamp is 12VDC. The wiring on the old lamp is that the wire connected to the black on the lamp is positive and the white on the old lamp is negative. I am not sure how they did this on the wiring from the motorhome. It is usually that the yellow is positive and the white is negative.
The new lamp has one black that is positive and the copper is the ground. Connect the black to the yellow wire from the coach and the copper to the white. The uninsulated copper will be fine as it is a ground and will not short or cause any problems if left uninsulated. If it makes you feel more secure then it would be fine to wrap the copper wire in electrical tape.
I hope this helps. If so, then please hit the accept button so that I can get credit for my support and efforts. If you have any further questions or concerns then please let me know.
Regards,
Jeff Myers
RV Mechanic
Owner of an RV Repair Facility for 9 years. 12VDC and 120VAC, ALL Appliances, Any and ALL problems!