Forum Discussion

mcewena's avatar
mcewena
Explorer
May 02, 2013

Odd 7 to 4 wiring problem

I've recently installed a brake controller on my RV as I'd planned to tow a trailer. I have confirmed it's working with a 7 pin LED tester.

Now I'm flat towing a car and I just want marker/brake lights, when I put in a 7 to 4 adapter and use a 4 pin LED tester I get left and right signals, tail lights but no brake lights even though the 7 pin tester showed the brake light working. I've tried 2 different 7 to 4 adapters.

Any ideas?

Thanks,

18 Replies

Show More
  • mcewena's avatar
    mcewena
    Explorer
    May 02, 2013
    TubaPete wrote:
    Sounds like your tow vehicle has seperate lights for turn and brake (amber and red, maybe). A 4 pin combines turn and brake into one light on each side. You need to install a wiring adapterin your vehicle to combine the two lights on eahc side into one. You can get it at almost any big box store, e.g. Walmart, that carries automotive supplies.


    You mean the 7 to 4 doesn't include that function?

    Thanks.
  • mcewena's avatar
    mcewena
    Explorer
    May 02, 2013
    TubaPete wrote:
    Sounds like your tow vehicle has seperate lights for turn and brake (amber and red, maybe). A 4 pin combines turn and brake into one light on each side. You need to install a wiring adapterin your vehicle to combine the two lights on eahc side into one. You can get it at almost any big box store, e.g. Walmart, that carries automotive supplies.


    MH brake and signal lights are separate. I have an led tester just like that and it reports things work as they should (although the back up light flashes slowly)

    I have a 4 to 7 adapter like this http://www.amazon.com/Reese-Towpower-74607-Wiring-Adapter/dp/B000CPI6VI/ref=pd_sim_sbs_auto_3 and a 4 pin tester like this http://shop.trailerlightcheck.com/Vehicle-Wiring-Tester-LCV101.htm connected to it just to rule out the marker wiring.
  • TubaPete's avatar
    TubaPete
    Explorer
    May 02, 2013
    Sounds like your tow vehicle has seperate lights for turn and brake (amber and red, maybe). A 4 pin combines turn and brake into one light on each side. You need to install a wiring adapterin your vehicle to combine the two lights on eahc side into one. You can get it at almost any big box store, e.g. Walmart, that carries automotive supplies.
  • enblethen's avatar
    enblethen
    Nomad
    May 02, 2013
    Do you have amber turn signals on MH and red brake lights on MH?
    If so, you need to add a combiner to have brake lights on the four pin.
    Verify your LED tester is not reading the electric brakes as brake lights.
    If it is one like this, the brake led should only come on when the brake controller is sending power to electric brakes. If it is on without brake controller, the MH is wired incorrectly.
    Circuit tester
  • RinconVTR's avatar
    RinconVTR
    Explorer
    May 02, 2013
    I think this issue is with the lights, if the tester says the plug output is good. What are you using for lights on the toad? Stand alone markers? I would confirm the work on another vehicle first, and if they still don't work return them. If you cant return them, you'll need to check how they are wired.
  • mcewena's avatar
    mcewena
    Explorer
    May 02, 2013
    jaycocamprs wrote:
    Brake lights on a 4-pin connector are wired with the turns. A 4-way plug is L turn/brake, R turn/brake, tail/marker lights, and ground. The 7 way RV plugs also combine brake and turn.


    Yes but I'm assuming a 7 to 4 adapter sends the brake power to both signal lights.
  • jaycocamprs's avatar
    jaycocamprs
    Explorer
    May 02, 2013
    Brake lights on a 4-pin connector are wired with the turns. A 4-way plug is L turn/brake, R turn/brake, tail/marker lights, and ground. The 7 way RV plugs also combine brake and turn.

About RV Tips & Tricks

Looking for advice before your next adventure? Look no further.25,141 PostsLatest Activity: Jun 14, 2025