I'm reading a voltage drop in my trailer wiring and wondering if it's normal.
Here's what I've found:
Flat four plug from vehicle reads 12.5V from ground pin to tail light pin without the trailer plugged in.
Flat four plug from vehicle drops to 10.5V from ground pin to tail light pin when the trailer is plugged in.
Light fixtures on trailer read 9.5V from when testing both "socket ground to socket hot" and "ground-screw-into-frame at rear of trailer to socket hot".
Resistance between trailer's flat four ground wire attached to trailer tongue and the ground at the sockets and the ground-screw-into-frame at rear of trailer reads about 2.5 ohms.
The side marker lights have no ground wire, using the self tapping screws that hold the markers to the trailer shell as the ground. The rear lights use a ground wire, with the ground provided by a pigtail to a self tapping screw into the trailer frame.
What would cause a 2 volt drop right at the plug when the trailer is plugged in and then another 1 volt drop at the fixtures?
Thanks!