Blowing trailer battery fuse

[JEdgerton]

Part-time I tow travel trailers to dealers. Lately I'm blowing the 20 amp trailer battery fuse in position 19. I've cleaned contacts on the 7 pin plug but noticed a lot of corrosion on the 4 pin one. Would this have anything to do with my blown fuses? I can't see how as the 4 pin doesn't provide power to any batteries. Also, I'm noticing sparking when I connect the trailer cables to the battery posts. If the trailer was connected to the TV could this cause the fuse to blow? I'm connecting the positive post first so I not sure why I'm getting sparks.



I'm not electrically inclined so any help would be appreciated.



John

 

[BHanna]

That's pretty strange. That wire looks like it goes straight from the fuse to the plug so if it only happens when you plug a trailer in, I'd suspect the trailer has a short.

But it sounds like you tow different trailers so if it does it with all of them, I'm stumped. Maybe a problem with your receptacle?

 

[jelag]

I don't understand why your connecting the positive post first... are you having to connect the battery on the trailer when you hook up to the trailer??

I'm going to guess that the manufacturer or dealer has the battery disconnected so that it won't run down as fast... . so lets assume you have a trailer with the battery at less than a 40-50% charge... you connect the battery and start to tow...

Now you have a battery that is very low and it want's more than 20 amps of current to bring the batteries up to full charge. . in doing so the fuse blows... this is a possible occurrence but not the only one. .

We tow a lot... we've actually ran an 8 gauge wire from the batteries (40 amp) on the truck to the trailer plug and a 8 gauge wire on our trailers including the ground so that we always get full battery voltage at the trailer and fully charge the batteries as soon as possible...

We've noticed at least a 1 volt drop using the factory harness. .

 

[JEdgerton]

Jim - yes, I put my own 12V battery in the trailer when I hook up. The battery is only used to support the breakaway brake system and to raise the landing gear on the 5'ers. My battery is usually fully charged when I start out and should be recharged as I drive. I guess what I don't know is how much it discharges overnight when I'm off the road. Peripherals like trailer radio and clock backlights etc would slowly drain it down somewhat. Unhooking the battery when not driving would solve that - if a low trailer battery is the cause of my fuse blowing.

 

[Road Dog]

If you're getting a spark on hookup then something is drawing power. I guess the battery. How do you know it's charged? A battery shop can properly test it. The truck's charging system is designed to trickle charge the truck batteries and won't fully charge the trailer battery. I use a separate smart charger to keep my camper battery charged between trips.

 

[HHhuntitall]

The trailer fuse also runs the turn signal and running light circuits for the towing package. They will function on the truck, but not on the trailer. If you plug it in and it's sparking, you have a problem somewhere in the plug, I'd guess. A wire may have come loose and be crossed with the running lights or such, so draws a lot of power when plugged in..... if the fuse doesn't blow until you turn on the running lights, I'd suggest checking that wire in the plug. Or if it blows when you turn on one or the other turn signals.....

 

[JEdgerton]

Thanks for the replies guys. I think I've found the problem. The previous owner wired a second 7 pin connector in the truck bed and spliced into the OEM connector wiring. The splices were corroded and full of gung and moisture. I've disconnected the second plug and put some 'liquid tape' on the OEM wires where the splices were made. I tested with a voltmeter and all seems well. We'll see when I hook up another trailer this week



John

 

[mrtrombley]

I've blown that fuse many times when hauling new trailers, usually when putting rooms in or out because they take so much power. I kept plenty of 20 amp fuses on hand. If you're getting a spark when connecting the battery, something was probably left on inside the trailer. Go in and make sure things like lights, etc are turned off if you can. There will always be some draw from minor things like radio clocks and gas sniffers, but they shouldn't take much current. As a precaution from draining my truck battery I always disconnected the trailer plug when stopped for overnight. Just remember to plug it in next morning! I used to leave a little note on my steering wheel, "plug it in". Worked well for me.