how can I get "alternator only power" from truck?

[Sutol]

Could you tee into the feed wire from the alternator to the starter/battery , that way the alternator would charge both batteries when the engine is running.
Or am I missing something

EDIT.. would need a diode to stop tariler trawing power from truck when engine off..dooh

 

[buickanddeere]

You may want to measure the charging voltage at the second battery once installed to see if you are actually getting enough voltage to charge at the full, desired rate.

So the charger voltage booster is located back at the trailer battery or up under truck hood? I don't see the gain of locating the booster under the hood then loose voltage all the way back to the trailer battery. Locating the booster at the trailer would also compensate for (-) side vltage drop.

 

[Travelover]

So the charger voltage booster is located back at the trailer battery or up under truck hood? I don't see the gain of locating the booster under the hood then loose voltage all the way back to the trailer battery. Locating the booster at the trailer would also compensate for (-) side vltage drop.

I'm pretty sure that the DC-DC converter charger is located close to the trailer battery, similar to a solar controller.

 

[CinderSchnauzer]

I would like to change my 7-wire center pin to provide charging power for an accessory battery. I only want it to be powered when the engine of the truck is running, that way the truck battery won't run down if things are left on while the rig is parked.

How do I get power from the truck only when the engine is running? I would rather not have to tear into the dashboards and spend all day poking at things with a VOM if I can just tap into the alternator cabling inside the engine compartment or something.

I have not read the whole thread & maybe someone else has said this in a later post. If you have a late model Chev / GMC they are prewired for an electric brake controller. There are two wires are hidden near the underhood fuse panel. The smaller of the two wires is to power the brake controller and the larger is to energize the charge hot wire in the factory installed 7 pin. After removing the fuse panel cover there are two studs in the front. The charge wire goes on the larger one.

If you have Chev / GMC go to Trailer hitch, hitches and bike rack (800)298-8924 and look up Tekonsha Prodigy installation instructions and pics so you can identify location of the wires and location of studs. It will also tell what size nuts needed for the stud - probably metric.