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Old 06-22-2014, 07:06 AM   #15
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I have a 40 amp breaker connected to the driver side battery A 10 gauge wire goes back somewhere as there are three outlets in the bed and one by the hitch. Lose about one volt by the time it gets back there. Batteries stay charged, but will not charge enough if they're way down. Do have what was mentioned, truck on 13.6, off 12.7. I think I need to unhook the unused ones.

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Old 08-17-2014, 06:03 PM   #16
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Is the 12v aux on the truck hot all the time or only when the key is on

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Old 08-17-2014, 06:07 PM   #17
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Originally Posted by tim delong View Post
Is the 12v aux on the truck hot all the time or only when the key is on
It should only be hot when the key is on.
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Old 08-17-2014, 06:25 PM   #18
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Originally Posted by MnTom View Post
It should only be hot when the key is on.
Not always. Fords from 1999 to 08 I know fore sure are, but not the Chevy's of that year. So the correct answer is that it depends on the truck.
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Old 08-18-2014, 06:45 PM   #19
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Get a VOM and check between pins 1 and 4 on the truck socket ignition on. This will check both sides of 12 volts coming from the truck, note voltage. If that's good... plug in the umbilical cord and unplug your 5er batteries both sides. Now check the voltage at the trailer battery cables. If you get 0 reconnect the negative trailer cable only and check battery voltage between ground on trailer and the + cable thats still unplugged from the trailer It should read near or at the voltage noted at truck socket. IF no, you have either a problem with the ground or the charge line in the trailer or in the trailer umbilical. On all my 5ers there was some kind of circuit protection at the trailer on the charge line. In a Jayco 5er it was an in line fuse at the battery. In my current 5er there is a circuit breaker under the front cover by the hitch. Remember both + and - must have a complete circuit between truck and trailer to complete the circuit.
In my tow vehicle I always add a # 8 wire from the stud on the alternator through a 40 amp fuse and onto a continuous duty starter relay pole, The other side of the relay a continuous #8 wire to the 5er socket. I do the same for the ground side of the socket too. I also generally add 4/0 cables from the neg side of truck battery to the frame, engine, and body, under the hood. Most tow vehicles are woefully undersized for charge lines. My 5er has 8 6 volt golf cart batteries. A miserable 12 gauge wire cant handle either the amps or the voltage drop over 50 feet and who even knows how the grounds are connected. I also add a # 8 wire from the umbilical plug lug in the 5er right back to the + lead on the trailer batteries with a 40 amp fuse there too. Now some here will say thats too big a wire because the trailer plug cant handle the load through its contacts. I can say Ive never had a problem with either may trailer batteries not charging or my plugs. That said, I always checking battery health, connections and making sure all is working.
Let us know what you find.
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Old 08-18-2014, 08:08 PM   #20
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My experience with GM trucks is they have never made up their minds how to wire for towing. Some have the wiring pre wired inside with a nice connector WHich for a while was in the fuse box you plugged the controller harness in installed the fuses and relays and were good to go then they changed the pin out but not the connector so if you had the wrong harness it would plug right in but would apply the brakes when the DRL went off. Then they gave up and went back to just running the trailer brake and charge to the front of the truck so you had to find the wires under the hood sometime under the master cyl sometimes you had to remove the under hood fuse box. So that is the problem with them every year and model has changes. I understand lots of people love them and they can tow fine but sure wish they would just pick a wiring plan and stick to it like Ford did. OK rant over If the OP has already checked his truck wiring I would follow the 7 way cord into the trailer most have a junction box in or near the pin box on a 5th wheel with it plugged into the truck check for truck power in that box. As another person said unplug the trailer and disconnect the battery. You want truck power and only truck power to test charging. If it checks out in the junction box go to the front near the jack legs usually on the drivers side there will be some breakers mounted with wires going to the jacks and to the battery. Leave your ground on the truck the entire time so you see only if truck positive makes it to the trailer. If you have power thru the breakers to the battery you have a bad ground so reverse the setup and trace the ground back to the truck. Hope that makes sense and helps.

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