I am adding a trailer hitch to the ml and want to know the best place to splice the wiring harness into the truck. the mb harness is 320 and the harness at etrailer is 65 but you connect the wires. Question, would it be ok to connect the wires just before the connector that came on the truck or connect them near the brake lights. Thanks Dan

There is a plastic interior knock-out in back on the port side of my "99. The female plug is just accessible. You can't get a male plug but tin and flatten your copper leads and they will stay in just fine.
One of the leads, red I'm sure, is B+ from the dedicated trailer fuse. With this, you can install a relay type, 4 to 3 wire converter box. All current will be through the fuse.
You can also put in some 8 ohm ballast resistors on the turn signal wires and switch over to after market LEDs.