Forum Discussion

johnxhc's avatar
johnxhc
Explorer
Nov 02, 2021

Trouble shooting the cause of Charge Line blown fuse

On my Class A (Ford F53 chassis), if I pushed the brake pedal a few times , the Charge Line fuse blew up, this is repeatable.When that happened, I lost power on Hot and trailer break on 7 way trailer plug
I looked under the RV, the wire for the 7 way trailer plug, everything looked normal and I did not see anything obvious such as damaged wire etc..How do I fix that?
I do have a multi-meter.
Any help will be greatly appreciated.
Thanks in advance.
Class A
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Nov 02, 2021
    If the trailer is attached one possibiliy is that the total amp draw exceeds the fuse, which can be corrected with LEDs. But first measue the amp draw on the brake and charge wire. Have you checked for the correct fuse size? Is the trailer battery good and how do you know?
  • enblethen's avatar
    enblethen
    Nomad
    Nov 02, 2021
    My first thinking is a poor ground connection. My thinking brake operation trying to back feed. Start by checking trailer connectings (umbilical cord bodies) for loose wire.
  • YC_1's avatar
    YC_1
    Nomad
    Nov 02, 2021
    Is this a new problem? That is, was it working at one time?

    If it was working then you need to take the connectors apart for an inspection. They often have loose wires that short and chasing that with a voltmeter may be incredibly difficult.

    If it only does it with the RV plugged into the truck then inspect the trailer plug closely. I mean take it apart carefully. Heck, a simple screw rattling around inside can drive you crazy.
  • johnxhc's avatar
    johnxhc
    Explorer
    Nov 02, 2021
    ArchHoagland wrote:
    Is there a trailer or toad plugged into that connector when the fuse blows?

    No, it is not...
  • johnxhc's avatar
    johnxhc
    Explorer
    Nov 02, 2021
    CA Traveler wrote:
    If the trailer is attached one possibiliy is that the total amp draw exceeds the fuse, which can be corrected with LEDs. But first measue the amp draw on the brake and charge wire. Have you checked for the correct fuse size? Is the trailer battery good and how do you know?

    No, the trailer is not attached...
    it is 30 amps fuse, which is correct size.
    no sure what you meant by "trailer battery"..
  • johnxhc's avatar
    johnxhc
    Explorer
    Nov 02, 2021
    YC 1 wrote:
    Is this a new problem? That is, was it working at one time?

    If it was working then you need to take the connectors apart for an inspection. They often have loose wires that short and chasing that with a voltmeter may be incredibly difficult.

    If it only does it with the RV plugged into the truck then inspect the trailer plug closely. I mean take it apart carefully. Heck, a simple screw rattling around inside can drive you crazy.


    Yes, it was working before.
    Ok, I will open the 7 way trailer plug and check.
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Nov 03, 2021
    With no trailer attached remove the fuse and reconnect the terminals with a 12V bulb. Then when the light is on then move, tap etc various areas to help isolate the problem. It could be anything that doesn't work including wires. A wire tracer can help and a DC clampon ammeter can help to isolate which connection to the fuse is drawing excessive current.
  • JRscooby's avatar
    JRscooby
    Explorer II
    Nov 03, 2021
    Problem will likely be found when you take the connector apart.
    In general, my go-to for fuse blowing is a amp meter that can measure when laid on a wire. (Snap-on, early '70s) I use a turn signal flasher to replace the fuse, follow the wire with meter. when Needle stops jumping, just passed the short.

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