RandyF150----

I'm lost....i have a 1999 F150 5.4l 4x4 with tow package.

At the 7 pin plug, the electric brake terminal (aka. blue wire) always has 12 volts when the truck is running EVEN with the power brake controller removed from the truck. So anytime i plug in a trailer with electric brakes the trailer brakes are powered all the time, the truck and trailer brake lights are NOT on when this happens AND i do NOT have the electric brake controller installed under the dash. it does the same thing with or without the brake controller installed.
i need a good wire diagram or need to know what feeds the electric brake circuit (blue wire) i've checked the brake peddle switch, wiring harnesses, fuses, relays and wire condition and can't find a thing wrong.

R&TBabich

Right there is a problem.
The trailer brake activate voltage, blue wire, should never be 12v.
The brake controller gets a 12v feed and adjusts the voltage applied to the brakes (blue wire) giving more voltage to apply the brakes harder.
The brake controller should be feeding the blue wire.
You should be able to check for continuity from the 7-way plug back to the brake controller connector under the dash.
The voltage usually starts around .2v and goes up to a maximum of 7v.
I've never seen over 6v on our Prodigy 3.
You need to trace back from the connector into the vehicle wiring harness to find out where it is shorted out to something with 12v on it.
Your truck may be miswired and what you are seeing on that pin (#3) is the "charging" voltage used to charge a trailer battery.

PerryB

Sounds like mis-wiring to me.

RandyF150----

thanks for responding and helping.

FYI- i have 12 volts at the blue wire in the plug under the dash too. i've check continuity to ground and between all the harness wires, they are all open between ground and each other.
i'm wondering where the blue wire all travels through from the dash plug? is it a straight line back to the rear trailer plug or is it going through any relays or modules? the manual i bought doesn't have any wire diagrams that even show a blue wire or the wiring harness for the trailer brake controller....thoughts?
i haven't done any electrical work or had electrical problems on this truck that i can remember, i've owned this for 14 years. i did have all new brake lines and hoses installed last summer but i don't know how that would cause this.

R&TBabich

Is this a new problem?
Have you connected a trailer that was working properly before?
The Ford wiring diagrams I have are for a 2002 Excur and a 2003 Exped and so far they look identical so I think chances are good they would apply to a '99.
Note: the C2142 pin #'s are for a 2002 Excur diagram, for some reason the connector is flipped over and the pins renumbered in the 2003 Exped diagrams.
The DB - dark blue wire goes from C2142 #6 to C2142 C4099 #3.
The DB line goes thru 3 other connectors and is open at both ends.
The 12v you see only when the engine is running makes sense.
The 12v is used to charge trailer batteries when the alternator is running.
A relay is used to cut off the 12v when the alternator is not running so the vehicle battery will not be drained when stopped with the trailer still connected.
There are usually 5 relays for the trailer signals, no relay is needed for the trailer brake level signal or ground lines.
If this is the first time use for your trailer I have seen different pin assignments for 7-way connectors than the Ford setup which is annoying.
I think the Ford pin-out is the most common "standard".

RandyF150----

this is a new problem. we unhooked my truck from the trailer tried two of my friends trucks (1500 GMC -2003 and 1500 Chevy -2009) had no issues. they both have the standard 7 pin plug also.
i'll check tonight and compare my 7 pin connector with the pic of the C4099 you sent me.

I bought an L.E.D standard 7 pin truck connector test plug and that shows the trailer brakes on also, BUT not the trailer brake lights. if i press the brake peddle the tester will light up the brake light test lights and keep the trailer brakes on also

R&TBabich

Is this a new problem since the brake lines were replaced?
Maybe a cable got pinched when the brake lines were installed.
Do you get the battery charge 12v on pin #5 of the 7-way when the engine is running?

RandyF150----

this could be a new problem since the brake lines were installed. not sure i haven't pulled a trailer with e. brakes until a few weeks ago.
my 7 pin truck plug is different than yours. the center terminal is round, is labeled #7 and uses a purple wire from the truck.

7 pin truck plug looks like:
1- ground, white wire
2-trailer brakes, blue wire
3-trailer running lights, brown wire
4-aux 12v bat. charging, black wire
5-L. turn/ stop lights, yellow wire
6-R. turn/stop lights, green wire
7-back up lights, purple wire ( round, center terminal )

truck plug under dash is 4 wire, colors - green, red, blue and white
i have 12 volts at terminals red and blue, with the truck running and with the brake controller not installed. 0 volts at green and white wires.
i'm guessing the red wire feeds power to the controller and the controller send voltage to the blue wire for the brakes.

my LED test plug does NOT light up the 12v trailer battery terminal when the truck is running either. so i either don't have the aux. 12v trailer battery option or it doesn't work and is part of my other problem.

hope this makes sense

PerryB

That first pinout diagram in post #5 is for the plug that connects to the trailer receptacle. That is NOT the pin locations you see when looking into the receptacle. If the brake wire is hot all the way back from the controller, the controller is defective. If the blue wire is still hot with the controller unplugged, you have pinched wires somewhere.
Also, there is only one standard pin configuration, it should be printed on the receptacle cover. Its an industry standard.

R&TBabich

That's why that diagram looks funky.
I didn't realize there is a connector on the back of the connector.
Here's what the 7-way connectors look like.