When I tow with my car the left blinker doesn't work on the trailer. There is a 7 pin round plug on the car, with a flat adapter to the flat pin on the trailer. I have had the same problem with at least 3 trailers, so guess it is the car. Can you please provide me with a diagram for the wiring, as when I pulled the plug apart there were 2 loose wires.

Round 7-Pin Wiring Diagram

• ? White Ground.
• • Brown Taillights.
• • Green Right turn / brakes.
• • Red Auxiliary power.
• • Yellow Left turn / brakes.
• • Black Reverse lights.
• • Blue Electric brakes.

Trailer Wiring Diagram and Installation Help - Towing 101

hope this helps

6 pin socket

6 pin plug

7 pin socket

7 pin plug

5 pin socket

5 pin plug

7 pin socket

7 pin plug

7 pin socket

7 pin plug

7 pin socket

7 pin plug

12 pin socket

12 pin plug

small 6 pin round plug & socket

1 tail, clearance - brown

2 left hand turn - yellow

3 right hand turn - green

4 stop - red

5 electric brakes - blue

6 earth - white

small 7 pin round plug & socket

1 left hand turn - yellow

2 reverse - black

3 earth - white

4 right hand turn - green

5 electric brakes - blue

6 stop - red

7 tail, clearance, side markers - brown

round socket

large 5 pin round plug & socket

2 left hand turn - yellow

3 earth - white

5 right hand turn - green

6 stop - red

7 tail, clearance, side markers - brown

large 7 pin round plug & socket

1 left hand turn - yellow

2 reverse - black

3 earth - white

4 right hand turn - green

5 electric brakes - blue

6 stop - red

7 tail, clearance, side markers - brown

7 pin round heavy duty plug & socket

1 earth - white

2 left hand rear , clearance and marker - black

3 left hand turn - yellow

4 stop - red

5 right hand turn - green

6 right hand rear , clearance and marker - brown

7 reverse/auxilary - blue

7 pin flat plug & socket

1 left hand turn - yellow

2 reverse - black

3 earth - white

4 right hand turn - green

5 electric brakes - blue

6 stop - red

7 tail, clearance, side markers - brown

flat socket

12 pin flat plug & socket

1 left hand turn - yellow

2 reverse - black

3 earth - white

4 right hand turn - green

5 electric brakes - blue

6 stop - red

7 tail, clearance, side markers - brown

8 battery supply - orange

9 auxiliaries - pink

10 earth - white

11 rear fog lamp - grey

12 auxiliaries - violet

Are sure that pin doesn't control the brake lights or blinker? In that case the on position of the ignition alone would not provide power. Have a second person engage the brakes and blinkers wile testing.Depending on the trailer type it could even be for reverse lights.

I would start by making sure the emergency break away switch has the plunger in it and it's working properly. If everything is OK with that then the 5 pin plug must be wired incorrectly. If you only tow the trailer with that truck I would suggest changing to a seven pin connector on the trailer. It would appear you also have a problem with the left trailer brake. They should work together.

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Trailer Wiring Diagrams 4 Way Systems

4 way flat molded connectors allow basic hookup for three lighting functions; right turn signal / stop light (green), left turn signal / stop light (yellow), taillight / license / side marker (brown) and a ground (white).

4 way tow vehicle side.
4 way trailer side.
5 Way Systems

Same as 4 way system listed above but adds a extra blue wire for brake signal or auxiliary power. Used on pop up camper trailers or utility / boat trailers.
5 way tow vehicle side.
5 way trailer side.
6 Way System, Rectangle Plug 3/4 inch by 1 inch 6 way rectangle connectors right turn signal (green), left turn signal (yellow), taillight (brown), ground (white). The red and blue wire can be used for brake control or auxiliary. Use on a small motorcycle trailer, snowmobile trailer or utility trailer. Can also be used as custom wiring on trailers with 3 light/wire systems. See "Tow Vehicle Taillight Wiring" below.
6 way tow vehicle side.
6 way trailer side.
6 Way Systems, Round Plug

Round 1 1/4" diameter metal connector allows 1 or 2 additional wiring and lighting functions such as back up lights, auxiliary 12v power or electric brakes. Note: The black (sometimes red) 12v and blue electric brakes wire may need to be reversed to suit the trailer. Check with a test light or VOM. Uses: horse trailer, travel trailers, landscaping trailer, car trailer, etc.

6 way tow vehicle side.
6 way trailer side.
7 Way Systems

Round 2" diameter connector allows additional pin for auxiliary 12 volt power or backup lights. Uses: heavy duty landscaping trailer, car trailer, boat trailers, horse trailer, travel trailer, construction trailer, etc. Check with a test light or VOM.

7 way RV flat blade tow vehicle side.
7 way RV flat blade trailer side.

I am guessing you mean the 7 pin trailer tow adapter.

the 7 pin RV plug itself



The 2005 trailer tow adapter wire diagrams

if you go to the parts store they make them ready to plug in you will have to just unplug the tail lights and plug the wire harness inplace of it then itll plug back into the original spot.

Did you check the fuse for the trailer tow adapter parking lamps ? This is a separate fuse from the truck's parking lamps.
Fuse #10 is the Trailer Tow parking lamps ( via the trailer tow parking lamp relay ) and this is the same fuse for the trailer tow reversing lamps ( via the trailer tow reversing lamp relay ).

If you did not get an owners manual with your truck ( purchased used ), you can download one from Ford :
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

Diagrams for the Trailer Tow adapter :

try http://www.etrailer.com/faq-wiring.aspx. This should help. Mike

I take it the blinkers and brake lights work ok when not hooked up to the trailer? If yes, then the wiring to the tow hitch is not hooked up correctly. How many wires to trailer pig tail connection? U can have up to 7 depending on what you tow. Check to make sure these wires are hooked up from the truck to tow plug correctly: 7 wired---
brown-Rt turn and brake light, yellow-backup, white-ground, blue-electric brake, green-tail running lights, black-battery charger, red-left turn signal and brake light. Let me know if u have something other than 7 wire, I'll get the wiring color and source info for u.