Battery charge issue while towing with F250

[Jsweber82]

Hey All!

I’ll keep this brief as I just typed up a long post and somehow got logged out before submitting.

My question is for everyone but for any F250 owners would greatly appreciate your feedback! After a recent 8 hour trip back from Fort Wilderness I realized my camper battery was drained down to about 50% from running the fridge and whatever else was drawing power. I checked the fuses in my truck and apparently have 2 labeled for “tow battery charge”. One was fine, one was blown. I suspect that was the whole issue so after searching several places including 3 Ford dealers I finally found fuses that I believe will work although they are slightly different than the originals. I haven’t taken a trip since to really test if it’s working right or not but hopefully that’s the fix.

My first question is, assuming the battery charge is working properly, what should I expect and is it enough coming from the truck to compensate for the 12v fridge running? Should my battery stay fully charged?

My second question, maybe more specific to the F250 owners is how
I can test the voltage coming from the truck to the battery charge? I can’t find which pin from the receiver plug would charge the battery, nor am I sure the best way to test it?

What is y’all’s experience with this and does your TV provide adequate power to keep the battery charged while in tow, specifically with your fridge running?

[NH_Bulldog]

I believe Ford only powers the 12v circuit when the trailer is plugged in and the truck is running. You should be able to open the junction box on the trailer tongue and check voltage while connected and running.

I do not have a 12v -only refrigerator by choice since we dry camp often. My brother has one though and he found that you absolutely need two batteries on the camper, (a solar panel helps too) because one battery doesn’t have enough reserve to power the fridge while towing since the truck only provides a marginal amount of amperage to the charging circuit.

[JRTJH]

First question: What year F250 are you talking about? There's a significant difference in a 1982 and a 2022 F250 wiring and fusing.

Second question: What trailer are you towing, what loads were on the trailer battery other than the refrigerator while you were towing? In other words, was the furnace on? An inverter, running any 120 volt equipment, any tank heaters energized?

Third: To answer your question about which pin in the umbilical "charges your battery", it's pin# 4, which is the first pin CLOCKWISE from the index tab on the truck. Ground is pin# 1, directly opposite pin#4. This diagram should help you locate the correct pins.

Fourth: The only place I could find the cartridge fuses (photo attached) that fit my 2015 Ford F250, was at an O Riley's Auto Parts when I had one blow. I've since ordered a set from Amazon: https://www.amazon.com/Automotive-PR...a-820529730862 I fully realize that I may never blow another one, but after spending all day shopping every parts store in Marquette Michigan and all the automobile parts departments without finding one and then driving to Escanaba to the O Riley's which had "ONE LEFT"... I now have my own in stock if I need another....

[Jsweber82]

Originally Posted by JRTJH

First question: What year F250 are you talking about? There's a significant difference in a 1982 and a 2022 F250 wiring and fusing.

Second question: What trailer are you towing, what loads were on the trailer battery other than the refrigerator while you were towing? In other words, was the furnace on? An inverter, running any 120 volt equipment, any tank heaters energized?

Third: To answer your question about which pin in the umbilical "charges your battery", it's pin# 4, which is the first pin CLOCKWISE from the index tab on the truck. Ground is pin# 1, directly opposite pin#4. This diagram should help you locate the correct pins.

Fourth: The only place I could find the cartridge fuses (photo attached) that fit my 2015 Ford F250, was at an O Riley's Auto Parts when I had one blow. I've since ordered a set from Amazon: https://www.amazon.com/Automotive-PR...a-820529730862 I fully realize that I may never blow another one, but after spending all day shopping every parts store in Marquette Michigan and all the automobile parts departments without finding one and then driving to Escanaba to the O Riley's which had "ONE LEFT"... I now have my own in stock if I need another....

Sorry, should have been more specific. It’s a 2020 F250 XLT 4x4 gasser and the TT is a 2021 Bullet 287qbs. Really the only thing I had running was the fridge. No lights, furnace or anything else running that would draw power. Unless the trailer brakes? But I always understood those were powered from the truck?Otherwise nothing else pulling power. I too had the hardest time finding the battery charge fuses! I checked a few local auto parts stores and a few Ford dealers who all kept trying to give me the wrong fuse. It looked correct in every way expect the base where it connects is different. Even had a Ford parts guy ask me where the fuse came from because he hadn’t seen it. Lol. I haven’t found the right one online at all and snatched up the only 2 I could find at the 3rd Ford dealer so hopefully they don’t blow again!

[JRTJH]

Here is a photo of the wiring harness that connects the truck to the trailer. As you can see, the LARGEST gauge wire in the entire harness is 12 gauge, and that's the trailer brake line. The next largest is the battery charge line which is 14 gauge. The distance from the engine compartment to the battery on your trailer is approximately 20', so that's a 40' "total wire distance".

At 40' total distance, the maximum amperage to carry 13.6 VDC is:

20 amp 6 gauge
10 amp 9 gauge
5 amp 12 gauge
2 amp 16 gauge
1 amp 19 gauge

So, as you can see, there's "precious little charging" with the 14 gauge wire. It calculates out to around 2.75 amps on the battery charge line. That's barely adequate for a trickle charge current rating, much less a "reliable charge line for a GP 24 or GP 27 lead acid battery.

In practice, most people find that after a full day (8 or 10 hours) of towing, their trailer battery may have charged about 20 to 30 percent. That's from, say a starting charge of 50% up to around 70 to 80%.

A tow vehicle is not a reliable means to recharge a depleted trailer battery or even to fully charge a partly discharged battery on a 2 or 3 hour tow. If you're ever in a situation of having a discharged trailer battery and need to use the tow vehicle to recharge it, you'd be better served to use jumper cables and get "maximum amperage regulated by the truck alternator" rather than rely on that "skinny feel good wire" in the trailer umbilical....