*HELP* Ford F350 Trailer Wiring Issue - Diesel Forum

tatuus · 07-05-2009, 05:50 PM

I have a small issue and was hoping someone could help me. I have a 28" trailer hooked up to my truck through a 7-pt Bargman.

The initial problem was the 30-amp fuse blowing that feeds the running lights on trailer and truck. I seem to have fixed that by going through the wiring and regrounding the factory wire harness and cleaning all terminals on the 7-pt Bargman (truck and trailer ends).

My last challenge is the interior lights. They do not work and seem to be wired to the "battery charge" section of the 7-pt Bargman. I have used a test light and there appears to be no power going through that wire. When tracing it back to the engine bay there is a Pollak circuit breaker in-line that IS getting power from an ignition switch on the passenger side of the engine bay but not getting through the circuit breaker. I bypassed the breaker and now have power to the midpoint of the pick up truck but NOT at the 7-pt truck plug.

I'm assumming this wire is a "hot" lead only when the ignition is on and it would be split to charge the trailer "breakaway" battery as well as supply power to the trailer interior lights.

Is there another fuse in-line between the circuit breaker/factory harness and the 7-pt plug that I'm missing?

Why wouldn't I just wire straight from the battery positive (with a fuse) to power the interior lights?

Thank You.

John

nashvillebill · 07-05-2009, 07:35 PM

The hot wire going to the trailer should be hot only when the truck is running. This is so the trailer won't drain your truck battery. The trailer battery is for operation of trailer interior lights, water pump, fridge, anything else in the trailer that uses 12 volts. The trailer battery also doubles as power for the breakaway brake switch.

Typical truck wiring comes from the battery to a fuse and relay, then to the receptacle on the truck. The relay is pulled in when the truck is running (the relay gets its signal from a circuit that's hot only when the key is on).

nashvillebill · 07-05-2009, 07:44 PM

Also, another reason you do not want the trailer's breakaway battery always connected to the truck's batteries: if the trailer battery hasn't been disconnected when you're trying to start the truck, the truck's starter motor will try to draw current from the trailer battery as well as the truck's battery. Best case it would pop the fuse or circuit breaker, worst case it could start melting the relatively long length of small wire....

tatuus · 07-06-2009, 12:10 AM

Thanks Nashville. Ok. I think I understand but have a couple follow-up questions. The way it's wired now the "battery charge", black wire from the 7-pt Bargman goes into the power distribution (under front of trailer) and straight to the interior wall switch. The "breakaway" battery doesn't receive a charge AT ALL. I guess they expected us to pull it out and charge it before every trip? Will the little battery be overcharged if you go on long trips?

Also, should I assume a relay/fuse is bad if the "battery charge" lead to the truck's 7-pt Bargman ISN'T hot?

Thanks.

John

LMJD · 07-06-2009, 08:23 AM

Quote:

The "breakaway" battery doesn't receive a charge AT ALL

Sounds like you have the small separate battery that powers your breakaway system. If so, it is totally isolated from the regular trailer batteries and the truck's charging system. It's not rechargable either.

Quote:

The hot wire going to the trailer should be hot only when the truck is running.

Not really, depends on the year, my original truck wiring has the constant hot hot all the time, running or not.

Quote:

if the trailer battery hasn't been disconnected when you're trying to start the truck, the truck's starter motor will try to draw current from the trailer battery as well as the truck's battery.

Not true, the constant hot first goes to the inverter which prevents that from happening. I've never disconnected mine for over 20 years and never known anyone who did.

tatuus · 07-06-2009, 10:45 AM

Thanks for the input.

So, what should I check to find out why there isn't power going to the "battery charge" on the 7-pt Bargman (black wire) output?

Is there a relay/fuse somewhere up in the engine bay?

Thank You.

John

tatuus · 07-06-2009, 05:46 PM

Update with answers! It appears as if the #18 30-amp MAXI fuse had blown. I swapped it out and viola we are hot to the interior lights! Now, I'm still not sure why it blew in the first place but hopefully by re-grounding everything I've solved the issue.

The next question is if I should take that hot lead and actually charge the breakaway battery (if it's a rechargeable) and wire from there to the interior lights.

Suggestions?

wittmeba · 07-07-2009, 12:08 PM

Sounds like your wiring was a bit old and just that could have caused the fuse to blow along with the ground issues you mentioned.

Just for edification. You mentioned you thought they may have expected you to charge the battery from an external charger. I dont think it would be wise (and maybe in viloation) for a trailer mfg to not have provide hot feed to the battery as it is the emergency source as Bill mentioned for your brakes. If you camped all weekend and almost drained your battery, when you depart you wouldnt have emergency braking but you wouldnt know it. You need the wire to charge the battery. Then you never need to worry...it should be charged when you arrive at your campsite.

Glad to hear you got it fixed. Dont forget to remove the bypass around the breaker.

tatuus · 07-09-2009, 08:19 AM

Hey Bruce,

Thanks for the input. A couple questions: After going through the wiring (pulling off the 5th wheel wiring that I don't use, cleaning up the grounds, replacing fuses etc..) I tried to start the truck and the starter wouldn't work (there was plenty of battery juice and all other electronics worked just no cranking from the starter). While looking around I noticed a small switch under the dash that was flashing red. After hitting the reset button on that switch the truck fired right up. Any idea why that switch was wired in?

Also, with the truck running (after resetting the switch) the voltmeter gauge in the truck seems to be much lower than normal. Typically, the voltmeter would show in the A range of N-O-R-M-A-L now it's in the O-R range. I put a meter on the batteries and it's reading 12.80 volts. Should I be worried here?

Lastly, what breaker bypass?

Thanks.

John