I bought a Tekonsha Prodigy brake controller with a direct plug in wiring harness for use with my 2000 F250 with the factory tow package and a 18' 1991 Fleetwood Wilderness travel trailer. I rewired the plug on the trailer to match the one on my truck and would like to verify that wiring before going any further. My lack of experience and ignorance makes me skiddish. I was told the biggest danger was in having anything other than the ground wired to the ground. I am unclear as to how to safely test for this.

Advice in this regard would be very much appreciated.

 

You have the 7 round plug? It came already wired, right? I don't know why you would have to have changed it. You should have just wired the plug on the truck and been done.... Did you have to rewire the trailer plug?

BTW, Welcome to the forum!

 

The previous trailer owner had an older F250 and had rewired the trailer plug for it. I changed out his round 7 to a flat blade 7 to go with the plug-in on my truck. Since he had spliced it with different colored wires and the pin outs didn't match, I'm a bit wary of what I came up with and would like to somehow check it before juicing it and frying something.

Thanks for your reply.

 

controller wiring
As for the plug under the dash one pin is a
hot 12v,(either Red wire old style or Pink new style);
another is hot when you press on
the brake pedal,(light green,old; red,new);
ground is White (old & new);
Blue is the power to the towed brakes from the controller.
The last pin is not used.
CHECK FOR FUNCTION ! My controller adapter fit this plug however the output was wrong!
Typical color codes and positions for a 7-wire connector.
1. Ground (white)
2. Electrical brakes (blue)
3. Tail, license and running lights (green)
4. Trailer battery (black)
5. Stop and LH turn (red)
6. Stop and RH turn (brown)
7. Auxiliary circuit (yellow) this is normally used for back-up lights on the trailer.
On the 4 pin connector at the bumper it will most likely be that 3 are hot and 1 ground return. The three that are used will be Left
turn/ brakes, Right turn/ brakes and running lights.

 

You can always just take a jumper from a hot source to any of the terminals and verify what they are supposed to be.

Click HERE if you need some other help.

 

Thanks much, Joe and Shorebird. I already had the controller installed and am not so much concerned about the truck end except as may be damaged by a wrongly wired trailer end. The info I have is consistent with what you gave me and that is how I wired the controller in the truck, and also how I think I re-wired the trailer plug. But I want to test it as you also both recommend.

So if I can apply juice from any hot lead and the wired item will function, can I hook up the trailer batteries and jump the 12V hot at the trailer plug to the other trailer leads at the same plug, except the ground, to see if the blinkers blink, etc. (not use the truck at all, at first)?
If I don't have it wired right and I put hot to ground, what would happen?

If this approach won't work because the trailer batteries are dead, could I connect a turn signal from the truck to that of the trailer and see if that works?

Thanks again.

 

To find which is ground, take a multimeter and do an ohms test to the frame. That is your ground. Or you can take a multimeter from hot(verified) and you should have 12v(+/-) when you find the ground terminal. To find your hot take the multimeter with the black on the frame and probe terminals with the red and when you get 12v, that it your hot terminal.

Yes, applying any 12v source to a function should make it work. IE turn lights, etc. But, the trailer battery terminal is to charge the trailer battery (I think)and really no way to test that one.

Also, what I did to verify my brake controller was to push the brakes down and checked the voltage at the plug. It should be less than 12v, like 2-4 range. The brakes should never be 12v.

I don't mean to sound demeaning, just trying to explain the best I can. If you have more questions let us know.

For a jumper, you can take a 12" piece of wire and strip both ends.

 

Thanks, Joe. I have an unused cheap multitester that I will try to learn how to use.

"To find which is ground, take a multimeter and do an ohms test to the frame. That is your ground." Sorry, which is my ground?

As you say, the trailer battery terminal may not work to power other trailer leads (though I don't know why current wouldn't flow both ways through it), so I guess I could come directly off the battery to test the other leads, like the turn signals?

 

yes.

Ok, you take the leads to the multimeter and put it on the ohms(200k) setting, will be a funky looking upside down U. Touch both leads together and the display should be zero. Put one lead on the trailer frame(bare metal around the tongue is fine) and then touch each of the terminals with the other lead. When the multimeter reads zero you have found the terminal which is ground. Do not apply power to this terminal!!!!!

The terminal that goes to the trailer battery may have an isolator on it, which only allows current or voltage to travel one direction. I don't know without looking at it specifically.

You can do this to the truck also, to make sure which terminals are which. IE, turn on the left turn signal, take the multimeter and put the black on ground(always black to ground), and then touch each of the terminals until the meter reads 12 volts, 0 volts, 12 volts with the pattern of the turn signal. The setting on the multimeter should be 20 V DC.

Does this help, or am I confusing this even more?

 

You, my friend, are helping a lot. With the meter in my hands your instructions make sense and I think I can handle carrying them out.

I assume your "yes" was in reference to my question about being able to get power directly from the trailer battery to apply to the turn signals and other trailer plug leads (except the ground) to check the wiring.

 

Yes, it was. Any 12 v source will work. Sorry, I couldn't edit my post when I realized that was vague.

 

Well, the readings didn't inspire much confidence, to say the least. They were a bit erratic, all over the place. However, the plug lead labelled (by me, at the time of the rewire of the plug) 'ground' did go to '0.' Unfortunately, so did the 'brake' lead (the emergency brake trip plug device is pulled on the trailer, though I don't know if that matters). The right turn lead settled in at about '.3.' The power lead was very erratic, as was the tail light. the left turn didn't budge from '1.'

Should the trailer batteries be hooked up for this testing (they are not)?

I'll try it again tomorrow with a clip attaching one lead at the ground location used by the trailer wiring to try to get the readings to quiet down a bit.

 

The above readings were with the multimeter on what? If you left it on ohms, you will always get a reading greater than zero between ground and any other terminal.

Since you located the ground, what you need to do is locate a hot source(i.e battery termimal +). Take a jumper and leave one end on the hot source and touch each of the other terminals with the other end. When you touch the running lights, all the lights will come on on top, left turn will work when you touch that terminal(won't flash though because the flasher is part of the truck), brakes will light up, etc.

Let us know if we can help some more.

 

The above readings were on the multimeter set to 200k ohms.

I wanted to be sure about knowing the ground terminal before applying juice to the other leads to verify them because of the danger of connecting the others to ground. ??

Does it matter that the batteries are not hooked up? I wouldn't think so.

Why don't the truck fuses protect the truck wiring (when it is hookrd up) in the event of an improper wiring at the trailer plug?

 

They will(truck fuses), as long as you are not applying juice to the ground. Blowing a 25 cent fuse is no big deal, but burning a wiring harness from front to back, fuse panel, etc due to a bad ground is a PITA. I know, I did that with a borrowed trailer. I fried my wiring harness from the plug to the fuse block, my light switch, etc. I now always check to make sure that I have a good ground.

Connecting the other terminals to ground is okay. Nothing will happen because there is no power in the circuit. The lights have a ground terminal in the lights themselves(the power has to have a way to get to ground). You can take a light bulb and touch a hot wire to it and nothing happens, or a ground wire to it and nothing, but both and the light works. You will want to connect the ground in the wiring harness to the frame(just to be safe). Then you can jumper the other terminals and see what happens.

Also, you might want to take the right turn signal lens off and check for corrosion. .3 is a low reading and tells me that there is corrosion somewhere. Maybe not, but it might be worth checking.