does ant one know where the 12vdc comes from to charge the battery on a trailer the pin for 12vdc has a wire on it but find no information in book on 7 pin plugs for this wire it red which is good but need to find out where it hookup to now I have no power on it
Very likely not OE from the factory. Likely you will have to trace the wire.
It should go to the chassis battery or place connected by large-gauge cable to the chassis battery AND should have an in-line fuse at the connection to the battery/other "place".
Also need a fuse at the toad battery end.
WIRE GOES LEFT AROUND ENGINE COMPARTMENT THEN INTO WIRELOOM BATTERY IS ON RIGHT SIDE NOT LEFT WILL LOOK FURTHER
If in doubt and you do not have a wiring diagram showing that it is done properly (with fuse and at least 10 gauge wire) REDO IT.
As Brett says, this is not standard/OEM wiring and would have been added by/for a previous owner who requested a charge line be run.
Not sure what coach you have. You might want to add the info to your avatar.
What Brett said will work fine. You might check the number on the wire, if it reads extra #XX, it may be disconnected at the front. It was normal to use one of the extra wires for a charge wire. You will find it exiting at the left front of the dash.
On our 97 U 295, I torched out the hole for the plug larger. Installed a seven round plug. Used one of the extra wires in the harness to the front. Added a 20 amp breaker.
I run mine off an ignition source from the electrical junction at the right front of the dash.
I also used an extra wire for trailer brake control, and activation light on my dash for my aux toad brake.
Chris