Factory trailer wiring Question

[MLeix]

My '04 QC 3500 is not getting power to the right turn and stop pin at the trailer connector (truck side). I checked it up to the connector right behind the left front wheel well and still no power coming to the connector there as well. All other lights work inluding all truck lights. All fuses check good.



Has anyone else come accross this? Is there another fuse somewhere that I don't know about?



Does anyone have a wiring diagram for the factory trailer wiring?



Thanks for any input.

 

[p-Bar]

Not sure if the 04 has a FCM if so the dealer needs to reset it . Just another gimmick to make money

 

[CKelley1]

p-bar is correct. this was a bad idea, the engineers did not consider things like wires rubbing against frame or a filament burning into and falling over on the other one. what most people are doing is to build a fuse box, relay setup to remove any load off of the pcm if you need help with schematic pm me with your email address and i will send you one

 

[BHanna]

There are separate fuses for the trailer lights so make sure you check the right ones. They're in the same fuse box under the hood as all the others and you have separate circuits for each side. They are marked so not too hard to find. I had a fuse blow due to a short in my trailer wiring and replacing the fuse was all it needed (after I fixed the short of course).

 

[Bob4x4]

p-bar is correct. this was a bad idea, the engineers did not consider things like wires rubbing against frame or a filament burning into and falling over on the other one. what most people are doing is to build a fuse box, relay setup to remove any load off of the pcm if you need help with schematic pm me with your email address and i will send you one

You are thinking 06 and newer

 

[MLeix]

I did check the trailer wire fuses under the hood, they were good. I also just changed the ECM (Whole nother story!!). Lights did not work before or after new ECM.

I have heard of some on this site having to change the fuse box because of some bad integral relays. Can anyone verify this and if so, did it fix the problem?



New ECM was due to a failure of the 5Volt sensor supply voltage. Good as new now.

 

[p-Bar]

You are thinking 06 and newer

So Bob 04-05 are fused and 06 above FCM or PCM ? is this correct?

 

[BHanna]

Did you check the fuse with a meter or just visually? You might try replacing the one for the side where the lights are out anyway just to see if maybe the fuse is bad.

 

[steved]

There is a set of relays (actuate the turn signals) under the fuse box, they are undersized/overfused. The fuze box will need replaced, there is a long thread about this in the towing forum.



When/if you replace the fuse box, replace all the fuses controlling the trailer wiring with 5A less fuses (in other words, replace a 15A with a 10A fuse) to protect the relay.

 

[TCDiesel]

Here it is Post 16. . https://www.turbodieselregister.com...smission-discussions/214406-05-part-03-a.html



On edit:Ryecreek Install the PDC From us, last I heard all was fine. . left here with 10amp in all trailer circuits.

 

[MLeix]

Well, I went ahead and ordered the relay and I am just going to remove the bad one and solder the new one in its place. Box was a pain to get into but once you get it open, the relays are right there.



The relays are tough to find and there was a $25 Minimum order for a $4. 30 part. So I have some extra relays coming if anyone else is going to attempt this repair. I can hook you up with the relays without the $25 Minimum.



Thanks for all the info on this post, you guys are great!

 

[TCDiesel]

I doubt That will work, and if the pulling unit requires more amperage than 10amp it will fry the circuit ( if hasn't been done already), I was hoping ryecreek would post the update after replacing his PDC one of the trailers he is pulling will occasionally blow the 10amp fuse in the new unit. If he would have left the 15amp in it would have been another $$$$ for a New PDC.

 

[MLeix]

All three relays are rated for 20amps which is more than the 15 amp fuse. Is it not possible that it is simply a failed relay? Only one of the three are bad after 84K miles. If it was a fuse issue, you would think all three relays would fail.

Anyway, I think I will try a $25 fix before I spend the $380 the dealer wants for a new PDC.

 

[TCDiesel]

Post # 10 Link, the relays are not the weakness its the Circuit board that is, also the PDC has (PCI) on some of the circuits (none of the auxiliary lights use this) but if there was some type of charge it may jump, then the cost will be in the 1000s for the repair. The ECM/PCM and IC,TIPM,FCM,DCM are all sendy. . I agree the 03/04 PDC are not strong enough and are poorly built and the components should take twice the amps for a safe unit.

 

[ryecreek]

sorry i missed this

you need a pdc as twest said it fries the circuit on the board itself and is nearly impossible to repair as thin as it is (beleve me i tried )

a new pdc is the fix with 10amps in position 46, and 47 bet ya got 15's in there now!!!

i have 2 03's both have been switched to the 10amps i have one trailer that blows the left about every 2500mi (not the truck i replaced the pdc) but they are 10amps not 15

used to pull the same trailer with the same truck i did the pdc in but it HAD 15'S IN IT same side same issue

now it blowes fuse instead of pdc's



you can get by like i described in my old post, BUT i'd only go tempary as there are way too many systems that have to communicate (ecm,fcm,pcm) they all work together including the pdc they (ecm,fcm,pcm)get voltage/amp draw from it

find a pdc install 10amps in 46,47 and you'll be good

PS

got one the right tlr is good on LOL!!!!

 

[MLeix]

PS

got one the right tlr is good on LOL!!!!

Ryecreek,

too bad we can't put both in one truck to make one good one!