Electrical Question Dome light related

First off the car is an 89 gt with a sunroof.

I was walking the junk yard and picked up a lighted rear view mirror out of a newer 95-00ish camaro. It looks just like the one in 94+ convertible mustangs.

I wired the hot to the feed for the vanity mirrors, and for the dome feed I pulled power from the existing dome light. For the ground I added it to the ground for the factory dome light.

Now when i plug in the mirror the cargo area light lights up... I got curious and looked at the dome light wiring diagram from a camaro and found that they switch the ground side and ford of course switches the power. I am thinking that i could just put a diode on the dome light feed to stop from back feeding the dome circuit.

I just want to make sure I am going the right directions with this one. Also if I can get some feedback on what size and type of diode to use.

Thanks in advance for any insight.
 
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