We got a new TT this last week. When I asked about the TT pulling charge current from the truck (2015 F-150 Screw), they said I should install "the relay". I have no idea what they were talking about, and when I went down to the local Ford dealer, they didn't seem to know about it either.

I did a little searching in the forum, but I can't seem to find anything. Based on the way the TT dealer talked, I think it is to prevent the TT from drawing charge current from the truck, but beyond that, IDK.

So the question is, what is this alleged relay, where does it go, and what does it do?

 

There is a relay that opens and closes with the ignition so the trailer only can draw current when the ignition is on. Check your owner's manual in the section that shows the fuses, etc. You may already have it in place, if you have a tow package. My 2010 did. Maybe all the newer trucks do.

Steve

 

I did check the manual, and there is nothing labeled "trailer charge" or something like that. There are several fuses/relays related to "trailer tow ", and the closest I can find is #79 that's called trailer tow running lights. It's installed, so I think I have the circuit, but charge voltage does not go to the trailer.

 

How do you know that? Did you check for voltage on the correct terminal at the seven pin on your truck?

 

The trailer does not show charge on the display panel.

 

That does not necessarily tell you anything about the truck. That simply says the panel is not showing a charge. There are a number of reasons your truck is good and even the battery is charging and not showing on the panel. Start at the truck and work from there. You may be correct, but there are other possibilities depending on how the trailer is wired.

Steve

 

I'll do that, but I still want to know about the relay, where it is, and what it does.

 

Relays are used to transfer large amounts of current with a relatively small amount to activate.
If you didn't use a relay, all of the draw would come down the line from a source where too much resistance could affect the amperage necessary.
A small amount of current will active the relay, connecting a strong supply of amperage to the necessary location, in this case, your trailer, too allow for less resistance and better/safer draw.
It's a much more effective way to get the proper amperage to your trailer.

 

I understand that. Question is, the dealer said I need one, but I don't know where to look for it.

 

I think yours is inside the pass side kick panel.

 

Is it called out any where in the owner's manual?

 

Mine is called out as " trailer tow battery charge relay" in the owners manual.

There will be a big fuse for it as well that should be called out the same. Usually it is a big square fuse, 30amp.

You need both to energize the wire. If you have the tow package, the dealer should have added the fuse and relay when they prepped the vehicle. Otherwise, they may still be in the glove box.

 

item 90 is the trailer charge Fuse


item 102 is trailer charge Relay.


for my 2012 F 250 anyway.

back of owners manual... "index" "Fuse & Relay" pages 331 and 332.


trailer dealer is not who you should talk to about trucks. and if truck dealer person does not know this .. find someone that is educated for Fords.
and as my screen name states..... my first Ford EVER... and I found it.

 

I've gone through the owner's manual, and I found six relays/fuses that say anything bout "trailer". They areNothing about "battery+" or "trailer charge" or such.

 

If I'm not mistaken, your camper's interior lights and the battery charging circuit get their power from the same red lead (on the trailer side, red/black on the truck side). So if you have working interior lights, your battery's charging circuit should be working too.
What used to be placed/found in the glove compartment of new vehicles is the fuse/relay for the trailer brake circuit. The vehicle would have a blue wire tucked up under the dash to supply 12 VDC to the trailer brakes, but needed the fuse installed to actually get power.