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Keep in mind that a truck with 12 volt batteries is setup primarily because of some high amperage requirement in the truck. If you're installing only 12 volt low amp accessories, it really doesn't matter which battery you connect to. Your accessory will only draw the necessary amps to operate.
If I'm wrong here I'm sure someone will correct me.
Adding lLED lighting to my toolbox and thinking of future amp(s), does it matter which battery we direct wire from?
My take of the OM is that the batteries are wired in parallel, so you could tap onto either (+) terminal. If you have upfitter switches, then that approach may be worth considering, as switches 5 and 6 can be configured for "Hot at All Times".
Going back to direct wiring, note that Ford recommends not using a battery common (-) terminal as a direct connection point (ref OM v2 page 245) , as this might cause inaccurate BMS measurements. This recommendation suggests to me that Ford has a very-low-value resistor in series with the battery common terminal(s) and is measuring current flowing in- and out of the battery(ies).
In other words, connect the accessory common wire to the frame or other similar location.
Another option would be to install and use a third battery -- a deep-cycle model -- and charge it from the seven-pin trailer connector.
Another option would be to install and use a third battery -- a deep-cycle model -- and charge it from the seven-pin trailer connector.
HTH,
Jim / crewzer
Jim: I don't have my SD yet, but, been reading in other threads about how these trailer connections are inoperable until they detect an active trailer connector attached. Am I understanding this correctly??? If so, is charging off the 7-pin an option??? Are u suggesting a 7-pin connector with only 1 connector / wire active (only the power wire)???
Maybe I've misunderstood some of the other info I've read. Just looking for some clarification. Thanks!!
Jim: I don't have my SD yet, but, been reading in other threads about how these trailer connections are inoperable until they detect an active trailer connector attached. Am I understanding this correctly??? If so, is charging off the 7-pin an option??? Are u suggesting a 7-pin connector with only 1 connector / wire active (only the power wire)???
Maybe I've misunderstood some of the other info I've read. Just looking for some clarification. Thanks!!
Fair questions. I basically understand the "trailer detection" requirement, but there's got to be a way past it in order to charge the battery in a slide-in camper.
I'm still researching this issue. Ford really could do a better job describing the connections and operation of various trailers and campers, especially considering how much work it put into camper compatibility testing.
Our truck's trailer towing related fuses appear to be the correct values in the correct fuse box locations. My theory is that the "smart" trailer battery charge circuit won't activate unless there's a big enough load; a DVM alone won't work. And, there do appear to be "work arounds".
Assuming we can get this to work, you'll need a seven-pin harness with two conductors: one (typically black, may be orange) for +12V battery charging, and one (white) for common.
More later!
Jim / crewzer
Update: I ordered a curt 7-pin adapter for LED trailer lights and a 7-pin pigtail harness. I'll see what I can figure out later this week.
Last edited by crewzer; Aug 28, 2017 at 10:56 AM.
Reason: Update
I received the Curt Model #57003 7-pin Trailer Wiring Adapter. I plugged my 7-pin trailer wiring tester (six LED indicators) into the adapter, plugged the adapter into the truck's 7-pin trailer connector, and started the engine.
The truck instantly recognized the "CURT trailer" I had set up in the trailer library, and the 12V charging indicator turned on (and stayed on) when I momentarily depressed the brake pedal. The charge circuit indicator turned off when I shut off the engine.
So, the tow connector circuits can be made to work without a physical trailer attached, and I see no problem using the 7-pin connector with this adapter to charge an extra battery. And, I'll keep the adapter handy for use with trailers equipped with low-current LED lamps.
The picture below illustrates the Franken-mess. The red LED illuminated at the bottom is the +12 battery charging circuit (+12) indicator, and the LED illuminated at 10:30 is the trailer marker lights (TM) indicator. As you can see, there's no actual trailer connected.
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