Of course you find the answer just after you admitted "I dunno ...".
http://www.jeepsurreygala.com/wp-con...7/m38-wire.jpg
The connector goes to the battery post on the starter. It connects directly to the 24-volt point of the electrical system. One connector goes out to the right fender and another goes back aft for radio power.
I am sure that this could be used for both external power for radios and as a jump-start connector.
As you could see on the earlier picture, it sat in a little recess with a capped connector.
Do you have the recessed metal and did any of the three tubs have a connector?