If doing electrical work it is important to get your components (wire & connectors) properly sized and your math correct.
84 Watts on 12 V is not 4 amp but is 7
16 ga wire is rated for more than 7 AMPs but this chart
and calculator shows more than 1 volt drop if you are 10' run distance or more from the 12 v source.
Low voltage can cause overheating or poor performance for some appliances.
I trust you used properly sized connectors at every step and soldered and shrink tube any splices. Hardware store solderless crimp connectors are not designed to handle vibration. I have always used properly sized brass or copper solder ring or spade connectors with heat shrink tub to support the sire as the solder will make the wire stiff and the flex failure point occurs at the end of the solder. Shrink tube supports the wire and transitions the vibration.
Note I have done wiring on race cars that have survived the equivalent of 50,000 mile durability testing with no electrical failures using the above guidelines.