Towing with low battery

[BoosTT]

I've towed my travel trailer when the battery in my trailer was low. My brake controller would say "check trailer wiring" when I applied the brakes. I only towed it about 15 miles and all trailer lights and the brakes still worked. The brakes might of been a bit soft for the first few miles, but I'm not really sure. I usually barely use them.

I think it's a law that you need enough battery power to apply the trailer brakes for 10-15 secconds incase the trailer becomes disconnected.

Anyone else notice this? Suggestions? How long does it take to recharge the battery via truck? Do you idle the truck for a bit?:confused:

[Outbackmel]

NOPE; I tow with a BIG BOY TRUCK and it has 2 HUGE batteries :bdance:

[f6bits]

I don’t think the trailer battery has anything to do with the brake controller. I base this on the fact that my TV, and hence, the 7-pin connector, has the one wire that goes to the brakes. My brake controller tells me how many amps it’s sending to the trailer brakes, so it’s getting this from the wire that feeds the brakes, not a wire that’s getting input from the battery.

You *do* need some battery charge for the breakaway brake system, but that gets charged via the AUX pin on the trailer plug, and I don’t think the brake controller has any insight into that circuit…unless perhaps it’s a fancy factory-installed controller that’s integrated into the TV’s electrical system.

[SteveC7010]

If your brake controller is advising that you check the trailer wiring, it means only the wiring for the brakes. As pointed out, the brakes are totally separate from the rest of the trailer wiring.

In particular, the trailer battery is only continuously connected to the circuits for 12vdc appliances, interior lighting, etc. plus the onboard convertor for charging off 110vac.

FWIW, you should be able to remove the trailer battery completely and still have the regular trailer brakes fully functional. Yes, you need the battery for the break-away to work properly, but the regular braking action is not affected at all by the condition of the trailer battery, even if fully discharged.

The break-away system is isolated from the rest of the trailer's wiring, and only shows a connection when the pin is pulled.

It sounds to me like there may be a broken or weak connection in the brake wiring somewhere that is causing the "check wiring" notice. That would also explain the "soft" braking action that you mentioned.

Charging the trailer battery via the tow vehicle is a slow process requiring several hours at highway speeds to bring a low trailer battery back up. Idling the TV for a half hour is not gonna do much. At idle, the voltage output of the alternator drops off just enough that it won't recharge a battery in a short time span. At highway speeds, the alternator should be putting out 13.8 vdc or so which will charge a battery much better.

[CarKath]

As others have stated, trailer brakes and battery charging are 2 separate issues.

I am only going to reference charging. I'll ask this simple question.

Do you have shut off switch for your batteries? Is it set to off?

[BoosTT]

I tow with a Ford Ranger 4.0L and was thinking some extra momentary current from the batterys was needed to help apply the electric brakes. My ranger didn't come with a factory wiring harness, I had to add it myself. I wired the trailer battery to the truck battery (with a fuse). Maybe I did this incorrectly.

In other words, if I have a dead trailer battery and good truck battery and connect my truck via the 7 pin: after time both batterys would be 50% charged rather than one good and one bad.

I was suspecting the alternator in the truck was working to charge the trailer battery and didn't have enough current left over to fully apply the brakes.

[BoosTT]

I did a bit of research on this and the likely cause is a bad ground. Oddly enough I had to replace a ground wire in the camping off season.:rofl:

So, I guess the trailer battery should not effect the trailer brakes.

[JRTJH]

I did a bit of research on this and the likely cause is a bad ground. Oddly enough I had to replace a ground wire in the camping off season.:rofl:

So, I guess the trailer battery should not effect the trailer brakes.

You're right, the trailer batter should not affect trailer brakes (except for the breakaway switch if it's connected to the trailer battery)

The first thing to check, I think, would be the brake magnet wires where they connect to the trailer wiring harness. Usually they are just wrapped together and a knurled electric nut twisted onto them. It's real easy for that connection (there should be 2 wires on each wheel) to corrode. I've seen brakes on new trailers right from the factory with corroded wiring.

[poochy]

also most of the older rv,s ground were grounded with truck by the two hitches connecting together so to elimate a bad ground try using another ground wire 2 see if your controler works better ?

[jje1960]

This is a very interesting post! I frankly don't know what standard is, if the brakes and emergency brake is wired through the battery and the battery is shorting, not sure what would happen if the emergency disconnect were to be required. While the trailer brakes may continue to work during tow, if an emergency disconnect were to occur and the battery was dead, will the trailer brakes lockup as designed?.... Not sure. Great post, more to investigate.

[smiller]

Usually they are just wrapped together and a knurled electric nut twisted onto them. That's bad, but I got you beat. I've seen manufacturers use Scotch-Lock connectors (those blue things that just pierce the insulation and aren't even reliable behind a dashboard, much less exposed to weather under a vehicle.) Amazingly irresponsible.

[larrym]

What is the TV? Try putting a multimeter on the 7-pin connector, typically the Bat (+) connector, looking at the receptacle from the rear, is the first to the right from 12 o'clock, the ground is the first to the left from 6 o'clock at the bottom. with the motor running, fan, headlights and tow mode active if equipped, it should be showing up to 14.7 V.

On my GM with the HD tow package with the extra in-bed harness, the wire is not connected under the hood from the factory, I found this in the manual and the dealer confirmed it, connected it for free. On the 7-pin connector, the brake pin is at the 5 o'clock position, test it with the brake controller 'squeezed", you should see voltage.