I have a 05 F350 dually 4wheel Diesel with the 6 liter engine.

It came with the factory trailer brake assistant.

I have no light on any of my trailers at all with a different truck everything is working fine.

I was hooking up my trailers and lately every time the 20 Amp blew while plugging it in., so replace Fuse 38 20 Amp under the dash board and i am good for a while.

Was on a longer trip with my Horse trailer and the fuse blew again, no biggy replaced the fuse and had light on my trailer again. After a a while the fuse blew again, replace again and so on. All other options on the trailer still work Blinker; brake lights the brake controller and even the inside light in the trailer.

So after changing out the fuse 38 20 amp several times i had to buy more and got also a few 25 Amp and used that. Now all the light where working for an hour or so and then started dimming down to appro. half the brightness. After an other hour or so they quitt working again. It is dark so i pull over and whant to replace the fuse 38 now 25 amps BUT the fuse is fine.......................................... i checked all the relays in both fuse boxes but some one told me there a several more somewher behind the cup holder so to speak under the radio.


Does anyone has anny idea on how to locate them a bit better, don't want to pull the complete dash board out. I took the gove box and the little compartment on the leftside out but can not see anything behind there.

Would appriciate some input.

Sincerely

Roger

 

The trailer tow park lamp relay is integrated into the CJB (central junction box) and isn't a servicable relay..

 

Hi Hayapower,

thanks for your quick Answer.

So if it is not serviceable means I have to change out the entire CJB ???? Where is that box located???

Sound expensive.... :--(((((

Might be the easier option to cut that wire and splice in a new one directly to a battery put a fuse in and a switch and done???!!!

But thanks for your knowable fast response.

Sincerely

Roger

 

The CJB is the interior fuse box.. I wouldn't write it off just yet, it sounds more like a bad ground or a wire chaffed/shorting out. Does the trucks rear park lamps/license dim as well along with the trailers? or steady bright with only the trailer affected? If it were the CJB/relay as the cause you 'could' release and remove the trailer park lamp 'out' wire from the CJB connector, then add a 'key on' fused wire to that leg as a fix.. I could supply you with the connector view, wire color/pin #.. If all the rear park lamps are affected, check the ground at the back of the truck.. It's on the left/drivers side frame rail rear..

 

As of now there is everything working just fine except the running lights on the trailer.

I have no Idea if those lights you asked for where dimm at the same time as the Trailer running lights.......was driving on Interstate till it quitt working and after pulling out and trying to replace the Fuse 38 with a 30 Amp i realized the light on the trailer did not come on so i checked the 25 Amp that i have used to replace the original 20 Amp and found that fuse to be fine.


So something has to be fried cause now the fuse is still fine but only the Running lights on the trailers (does not matter what trailer i use) will just not come on anymore. I tried my son's truck on the horse trailer and like expected everything works.

as of now i am out of ideas............where to ckeck anymore ...even took out the Main Fuse panele under tye dashboard but all those wires are so short that i just can't turn the box a bit to look for a bad or burned wire on the back......

 

i will for sure check the Ground wire, but don't think that is the cause.......everything else was working brake lights the Brake controller and of course the Blinker, but even all the inside Light in the trailer worked just fine if there would be some trouble with the ground??????????? allll should be effected???????

 

The question about the ground was to take it out of a possible cause.. If it were bad or a poor connection, you should have the trucks rear lamps affected as well.. High salt/corrosive area's like to challenge the ground attachment there, or even possibly a connection problem/short at the back of the trailer adapter plug.. If the trucks lamps work 'spec', and the only thing affected is the 'trailer park lamps' (tests dead at the rear of the trailer plug) then I'd check/test the connector on the back side of the CJB for 12v out on the BN/WT wire.. I can send you a pic of the connector view. If 12v is present on that wire/pin, then the problem is more likely between CJB and trailer connector.. The trailer lamps power distribution on back to the trailer connector goes through 2 other connectors I think. If there's 'no voltage' on that wire on the back of the CJB, and you 'add' a test wire/12v and the trailer lights come on, then the problem is most likely in the CBJ/trailer tow park lamp relay.. You should be able to get a continuity light probe, or meter test lead at the back of the CJB to check for power distribution there..

 

like you told me to i checked the ground wire under the frame and it is in good conditions.

Sending me the Info would be nice.

I don't know where to check on the back side of the panel.

Thanks for all your Help so fare.

Sincerely

Roger

 

Sent you a PM..

 

Hayapower - I have a 1999 F-350 gas dully. It has the same problem of no trailer park lights. Does it have the same trailer tow park lamp relay you have talked to others about? If so what is the PM you sent to Merker? Would it help me?