Ken -
The 4-pin connector is intended for lightweight utility trailers. It is missing some of the functions that a camping trailer such as a TM requires.
The 4-pin connector carries 3 circuits plus ground. The 7-pin connector carries 6 circuits plus ground. The circuits are these:
. Connector. . . . . . . 7 pin . 4 pin
1. Left turn/stop . . . X . . . . X
2. Right turn/stop. . . X . . . . X
3. Running lights. . . . X . . . . X
4. Trlr brakes. . . . . . X
5. Trlr 12v charge. . . X
6. Trlr backup lghts. . X
7. Ground . . . . . . . . X . . . . X
As you can see, the 7 pin connector carries three circuits that the 4-pin connector doesn't have. These are the trailer brakes, trailer backup lights, and the 12 VDC trailer battery charge line. There is no way for an adapter to create these functions. You must add wiring from the engine compartment area to the rear bumper, and mount a 7-pin connector there.
Note that if you go to an on-line RV parts site such as e-trailer.com, you can find what they call a 4-pin to 7-pin converter. This is a simple device that simply picks up the 4 wires from your tow vehicle's 4-pin connector, and routes them to the proper pins of a 7-pin connector. In other words, they do a mechanical conversion - you can plug the TM 7-pin connector into them. But they do not create the missing functions.
Bill
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