Yeah, I was thinking the same about splicing in a generic replacement relay. Beats buying a whole new box.

Steve

 

Yep, key off, flip the lights on you should have power at the CJB. Glad to see you are tracking it down.

 

Ended up being an issue somewhere between the drivers side door and the rear of the truck on just the running light wire? Ran a new wire along the harness and spliced it in front and rear and they work fine now.
Thanks everyone

 

Hello, this is my first post. I too have an 04 F250 and just this weekend==no trailer tail lights. Everything else (turn signals, brake lights, etc worked). Reading the above posting was deja vu. Fuse 38 was blown. Replaced it,, still no voltage at connecter in front of trailer plug. Reviewing my electric diagram--in service manual--and checking voltages everywhere I could--have concluded that the relay "fried". Where is this thing? Is it not a plug in relay--that can be swapped out. Serice manual I have--along with owners manual is not clear at all as to this relay location, etc.
Thanks for any help.
Gerlad1

 

It's made into the fuse box, you cannot replace it unless you replace the whole fuse box.

 

Hi,
Well, did some more "trouble-shooting" of my loss of power for trailer tow/park lights.
No voltage at back of truck on brown/white wire.--
My truck is 2004 F250 fx4 diesel. Found out//by pulling on them,,, that all relays in the CJB are removable and replaceable.
However, the wiring diagram I have shows that the Parking Lamp trailer tow relay is in the CJB. I cannot find it. Have voltage on both sides of fuse 38 but no voltage on brown/white wire going to back of truck with truck lights on.
My diagram shows that only problem can be a break in the wiring from the CJB and the back of truck OR a back relay. Does anyone have a wiring diagram that shows which relay number corresponds to the parking lamp trailer tow relay?? My diagram shows that if the brown wire--park light wire is "hot" I should have power through the relay to the brown/white wire. Surprised my diagram and owners manual does not identify the park light relay.
Any help will be appreciated. tried leapfroging relays but no help.
Gerald

 

I am pretty sure you will never find it. You do have replaceable relays in the central junction box (fuse box under the dash) but the trailer tow parking relay is not one of them according to the factory manual. The factory manual lists this relay as "not serviceable".

 

Thanks for the help and advice on the relay thing for my non-working parking lights for my trailer connector.
Went by Ford place today,, and they let me borrow their wiring diagram/connector book.
Found out Franklin was right--relay is physically embedded in the CJB and can't even see the damn thing with the CJB pulled out. Rather than spend the $289 + tax for a new CJB--I did as advised and spent about $15 at O'Reilleys on a relay, clips, etc and spliced one in behind the CJB. Now have power at plug on back of truck. All I have to do is reinstall the CJB and dash parts. Phew! Bet some Ford engineer gets excited every time someone has a short in their trailer lights and the relay goes out. What a bum design!!
Gerald

 

I am not the greatest mechanic but I would sure like to know how to do the bypassing of the cjb relay for my running lamps. My truck is at the dealer for a coolant loss problem and also for the trailer running lamps. They told me 530 bucks to replace the CJB. Can anyone explain how difficult it is to take that off and put in a seperate connection so I don't have to spend the 530 bucks. Is it to tough a job for a drywaller to handle? I just called the dealer and they told me the CJB was 200 dollars. Is this a part I could just unscrew from under the dash and unplug and plug the new one back in and if that is the case do I need to disconnect the batteries. Would something have to be reprogrammed by the dealer?. As up can see I am not a mechanic but if I could save 300 dollars I sure would like to!

Thanks
Dave

 

I don't have a newer truck like these, so I am only going by what I see in the wiring diagrams. Maybe one of the other guys who actually did it will have some advice.

But looking at the diagram, there is a brown/white wire leaving the fuse box and going to the rear for trailer running lights. Find this wire and cut it.

Go to the car parts store and get a Bosch type foglamp relay and some slide on connectors to connect the relay. Also get some "fuse taps".

The original fuse for this circuit is #38. Pull this fuse out, and with a testlight find which side has power with the running lights on. Hook the fuse tap to the opposite side of the fuse that did not have any power, and re-install the fuse.

Run a wire from the #38 fuse tap you installed to the common relay contact terminal on the new relay. Hook the brown white wire you cut to the other relay contact terminal.

Tape off the other brown white coming from the fuse box, just in case some day the old broken relay decided to work(don't want it to short out).

You should have a running light fuse for the truck running lights(don't know what number fuse it is right now). Put another fuse tap under that fuse, and run it to the new relay coil terminal. Hook a wire to a good ground somewhere under the dash, and run it to the other relay coil terminal.

What will happen is when you turn the truck running lights on, this will activate the new relay(it will click). When that happens, the relay will connect the #38 fuse tap to the brown/white running to the trailer, and turn the trailer lights on.

 

I have a 2004 F250 truck and also did not want to spend the $500 or so bucks to replace the CJB just to get my trailer tow lights to work after the "built in" relay crapped out.
I went to the auto parts place and bought some 16 gauge wire, some 16-14 guage quick splices, some female blade connectors and a 30 amp relay, an in line fuse connector with 20 amp fuse (all for about $20 total). I already had a crimping plier. Another $10 or so if you don't have one of these.
I disconnected the battery, unbolted the CJB (only 4 bolts) and pulled down the CJB. I found the brown wire--which is the headlight/parking light on wire and the brown and white wire--which is the one which goes to the trailer park lights. Using the quick splice,, I spliced a wire into each of these--not easy since there isn't a lot of room--but do able. Then I used a blade connect wire an in line fuse to tap into a always on unused fuse spot in the cjb. Basically I did not want to cut any wires,, so I tapped into the brown and brown/white wires,, follow the instructions on the relay package. You run a fused hot wire and tie it into the proper plug on the relay, another one to ground on the relay and the proper relay pin ties to the brown wire and the other pin goes to the brown/white wire tap-in.
Took me about an hour to do this. If you aren't comfortable about doing this, I suggest you find a auto repair shop that does auto electrical wiring.
I was orignally not comfortable about pulling out the cjb, etc. but turned out to be a piece of cake for me. Saved me several hundred dollars and works fine now. Good luck.
Gerald

 

Thanks Franklin and Gerlad I definetly will be attempting this. When I asked the fellas at the dealership about somehow doing this they acted as though this would be nearly impossible and very foolish, but it appears they were not correct. When I get my truck back from its coolant fix I will attempt this repair. I will let you guys know how this works out. I just joined this forum today and I may have all ready save 500 dollars.

Thanks again. Please keep checking I may have some questions in a day or two!

Dave

 

Franklin and Gerlad just to update my trailer wire situwation. I called the dealer and told them I would be fixing this problem myself. They responded they could run a wire form the battery to the trailer hookup at the back of the truck. Then put in a relay and in line fuse. Funny how now it was possible to fix without replacing the CJB!!!!!! I said I had gotten some great advice from this forum. I explained it to them and they asked if I would fax this info to them. I did and they told me they would do your fix for about $145.00. I went ahead and had them do the repair per your fellas instructions. Which by the way they agreed was a better repair than there idea. I know I paid to much but still much better than the first price. I felt like if I didn't let them do this work as all other work was under warranttee they would have gotten my $ somewhere else. In the future I will be sure to check this forum for any repairs that I can make myself. Had I consulted here first I assure you I would have done this myself. I asked them if they would give me a bonus rebate check on the repair for your great advice but they declined to do so.

Thanks again for the great advice and I will look here first in the future.

Dave
PS
My coolant problem was the oil cooler or something of that nature and not a head gasket, I was very pleased to find that out. My truck is a 05 psd with about 58k on it.

 

Hey all,

I'm having a similiar problem except my running lights are staying on all the time. I've posted this a couple of times but the response has been slow. The problem started when my wife put the 7 way in upside down and know I have constant power to my trailer running lights on the 7 way and 4 way plugs.

Thanks,

amckinney

 

I want to thank all who posted about this problem. I followed the above instructions and wired in a new relay. Connected to the brown/white wire coming out of the upper left hand corner of the CJB, aha fire on the brown/white when lights turned on. Still nothing at the rear plugs. I pulled the left hand kick panel and started there. Pulled my previous tap and moved it to the brown/white under the kick panel. alas success. Both the 7 pin and the 4 pin light taps are now working. Thanks guys you were a BIG!!!! help. jim