No 12V power to trailer

f6bits · 11-12-2012, 10:30 AM

When I bought my slightly used 2009 F150, there was a little baggie in the glove box with some electrical goodies for towing. Part #AL3T-15A416-AA. Since all *seemed* well, I didn't use it, and subsequently lost/trashed it.

I've since put a High Power relay in location #9 and a 30A cartridge fuse in location #21. I still don't seem to have power.

Anybody know what I'm missing? I took my best guess on the two parts and now just wish I could find that baggie. I've been Googling for the past day with no luck.

f6bits · 11-12-2012, 11:10 AM

So I checked my pins. I have ground and +12V on the pins opposite each other in the 7 pin circle. With my trailer battery removed, shouldn't I be able to turn on lights if the trailer is plugged into my truck? I'm just trying to find out of my battery is charging when I'm pulling my trailer.

**hankpage** · 11-12-2012, 12:04 PM

With everything connected you should see an increase in voltage at the trailer battery with the TV running. If voltage is over 13.5v dc the battery should be charging. Check the trailer end of the 7 way the same as you did the TV end and you should see voltage also if all is well. JM2¢, Hank

When you say "turn on lights" if you mean interior lights you need the battery connected or shore power. Marker lights have their own circuits and will work without a battery.

Big Boy w/ Big Toys · 11-12-2012, 12:20 PM

Here is a diagram to make sure you have the right pins.

As far testing....check your trailer battery first with nothing on and disconnected from truck. For a fully charged battery should be about 12.4 to 12.8 volts. Then to see if you are charging check the 12 volt pin to ground and see the voltage output reading on the tow vehicle. Then with meter hooked to the battery, plug the harness into truck, reading now should be around 13.2 to 14 volts depending on load. Also should be close to what u saw on truck pins, but remember load.

So when you added ther elay this was in the underhood fuse box. If U still don't have power I also think there should be a 30 amp large fuse that needs to be there. I have F350's so guessing on location of fuse box. But that baggie full of tricks everything needed to be installed to get proper trailer functions.

f6bits · 11-12-2012, 12:33 PM

BBBT, That "12 Volt Power" pin is live with the engine running.

Hank, I'll check that voltage with and without the engine running. I didn't have my voltmeter with me at the trailer today. I assumed that the 12V from my truck would power my interior lights just like my battery would. That was my test to see if to see if my trailer was getting power from the truck.

Where does the trailer end of that 12V feed go? I've never crawled under the A-Frame to explore that part of the wiring.

**JRTJH** · 11-12-2012, 05:10 PM

I don't have my trailer at home, and it's too dark and cold outside right now, but if I remember correctly, there is a relay circuit in your Ford that disconnects the tow vehicle from the trailer battery when the key is turned off. So, unless your truck is running, you will get zero volts to the trailer. Next time you want to double check function, connect the trailer to the hitch (it's a second ground), plug in the connector and start the truck. With your trailer battery disconnected, you "should" have lights inside your RV. Turn off the truck and they "should" go out.

That circuit is in the system to protect the tow vehicle battery from being discharged during camping. That will "assure" that you can start the tow vehicle even if you run the furnace all night and deplete your 12 VDC in the trailer.

f6bits · 11-12-2012, 05:32 PM

Quote:

Originally Posted by JRTJH

With your trailer battery disconnected, you "should" have lights inside your RV. Turn off the truck and they "should" go out.

But I don't, and that's where I'm stuck. The 12V pin on my truck's plug is working as it should. As a footnote, this is the first time I'm checking into this. I just added the fuse and relay in my truck to get 12V to the power pin. Up until this weekend, I just assumed it was working and then discovered that it's normal for F150s to be delivered without the fuse and relay installed.

**JRTJH** · 11-12-2012, 06:23 PM

I just went out and checked my engine compartment fuse box. Yeah it was cold and dark, but what the heck....

Anyway. There are two relays and one fuse for trailer towing. Actually there are more, but they aren't involved with any of the charging system.

There is a relay in these locations: #6 (trailer tow park lamp relay) and #9 (trailer tow battery charger) and the 30AMP fuse in #21 (trailer tow battery charge).

I can't remember if my truck "extra package" had one or two relays, but I'm thinking there were two relays, #6 and #9 in the package in addition to the fuse.

Double check your underhood fuses to make sure you've got relays in #6 and #9.

I'm thinking you just don't have something plugged in under the hood, I wouldn't go changing out wiring under the truck just yet. If you do have both relays and the fuse (make sure it's good) let me know and we can go from there.

I just thought of this: One time, I had a problem with no power for right turn signal and trailer brakes. There is a connector on the back of the truck end of the plug. It had separated slightly and wasn't making good connection. I unplugged it, added some dielectric grease and plugged it back in. It's all been working good since then. You might just reach under the truck on the back side of the plug and wiggle the connector just to make sure.

f6bits · 11-12-2012, 08:16 PM

Thanks for braving the cold for me. However, the problem definitely isn't with the truck. It's sending the power, but it seems the trailer isn't doing anything with it. I've done lots of plug wiggling, but my next step will be to whip out my trusty old AVM (analog voltmeter).

If only SAD could crank out one of his handy schematics that explains this.

**JRTJH** · 11-12-2012, 09:09 PM

On your trailer, there is (or should be) a 20AMP circuit breaker on the charge line going into the battery. It looks like an old oil filled capacitor, kind of oval with a red plastic cover. They are notorious for corroding internally and not functioning. You may check there first before you get too far into tearing out the wiring. And, in case you haven't been keeping up with the older topics, there are no wiring diagrams for any Keystone products, so you're pretty much left to your own devices in trying to figure out what goes where.....

deadeye · 11-13-2012, 04:48 AM

On my Ford F150 2002 you need to have the key in the on position to have power at the trailer pin. It will not work in the off or acc position.

f6bits · 11-13-2012, 06:10 AM

Yep, deadeye, key is on, truck is running and there is power at the trailer pin.

JRTJH, thanks for the tip on that breaker. That's one thing I was curious about. I'm guessing it's mounted on the A-Frame somewhere. If you haven't seen one of SAD's hand-drawn schematics, you're in for a treat.

Javi · 11-13-2012, 06:20 AM

On my 2012 Passport the trailer battery terminal wiring goes to the converter/charger thingy.. no battery... nothing works even if hooked to TV..

f6bits · 11-13-2012, 05:42 PM

Quote:

Originally Posted by Javi

On my 2012 Passport the trailer battery terminal wiring goes to the converter/charger thingy.. no battery... nothing works even if hooked to TV..

Thanks. So do you think it's charging your battery? I expect to get back to my trailer Thursday after work and trace the circuit.

camper 2010 · 11-14-2012, 05:08 PM

JRTJH in the last post is correct. The beaker should be mounted on the trailer tung or close to your battery. On my 27RLS, it has a 50 amp braker for the trailer electric supply and a 20 amp for the brake system.

f6bits · 11-15-2012, 06:35 PM

Found it, but I'm not sure how it works. I took a picture:

A is the top left, B is the bottom left, C is the top right, and D is the bottom right

"A" goes to my 7 Pin
"B" goes to my battery and my emergency brake thingie
"C" probably goes to my converter
"D" goes to "B"

A to B seems to be Open.
A gets 12V when my truck is running, but not when the truck is off.
B gets 12V when my battery is connected. Does not get 12V if battery is disconnected and my truck is running.

Is the A/B gizmo the circuit breaker? Is it supposed to be a closed connection? Does it reset, or do I have to buy a new one? The C/D gizmo sure acts like it's a closed connection.

If I jumper it, is that a bad idea? I'd really like my trailer to charge when I'm driving.

f6bits · 11-15-2012, 07:58 PM

Now that I see it in print, running a jumper to bypass a breaker is a bad idea. I saw one schematic where the 7-pin connection is attached to the same post as the converter, so that would be my C post.

That should at least get me limping along until I further investigate that first breaker.

outwest · 11-15-2012, 08:57 PM

Just throwing this out there - that big red box to the left in the pic (cut off in pic, barely showing on left edge) is your battery cutoff. Is it on? Dial on it should have 4 positions: off, use battery 1, use battery 2, use both batteries.

Javi · 11-16-2012, 04:14 AM

Curious as to why you think it's not charging the battery when the TV is running and hooked up..

As I said earlier... without a battery hooked up in the trailer the converter isn't going to allow power to the lights and accessories in the trailer.. it is a safety feature...

Easiest way to check the block is to disconnect the wires and cable the use an ohmmeter... it should be closed..

BTW it would take several hours to completely charge the battery from the trailer connector on the TV.. It is not the same as the charging circuit on the TV it is primarily there as a trickle charger to maintain the battery charge...

f6bits · 11-16-2012, 06:54 AM

out west, yes, that's my battery cutoff. It only has two positions and is set according to my need.

That breaker should be a passive device, normally closed. But when I have some time, I'll completely remove that one and examine it.

I've never heard that the converter won't pass power to the lights without a battery hooked up. I didn't even think a battery was necessary except for the brakes in an emergency (and boon docking).

My batteries are mostly charged, but I'm just trying to get as much charge into them before I set up camp this weekend. I'll have my generator, so I'm not all that concerned. I'm just trying to get this newly discovered feature working.

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