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3rd Gen Ram Tech2002-2008 Rams: This section is for TECHNICAL discussions only, that involve the 2002 through 2008 Rams Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.
I'm new to this forum but have seen several posts on this topic before and need a refresher. I have a 2005 Dodge Tam 2500 diesel with a trailer tow package. Yesterday, while towing a trailer, was informed the left turn signal and brake light on the trailer were not working. All the lights on the truck work fine but the 7-prong plug and 4-pronger for trailer connections are both dead on the left side. Fuses look good, wires look good but when the trailer is plugged in and the left turn signal is on, the relay does not ping like it does when the right turn signal is on. I believe it's a bad relay. Some say the trailer light relays are built into the IPM and the whole thing needs to be replaced. Others say they were only built into the IPM in 2006 and later models, so should be replaceable somewhere. Still others say a simple flash or reset may resolve the problem. All suggestions welcome.
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Welcome to the site. You can find the 05 Service Manual in the links in my signature. Download it and go to the wiring section and find the schematics to the 7 pin tow and use them to help trouble shoot.
There is a fuse then a relay in the power module. Not sure if you can get to the relay. You could attempt to test at the connector. It is supposed to be C1 pin 5 if I read the electrical diagram correctly. The relay is probably better because you can check all the pin on the relay. Pin 30/86 on the relay should be 12v. Pin 87 is the output to the trailering harness and Pin 86 is to the control module. If you see the voltage change at Pin 87 then you don't need to check the other pins. You might want to check at the 7/4 pin connector on the bumper first.
Fuse checks out fine. The 7/4 pin connector on the bumper is dead on the left turn/brake light. Relay does not ping with the left turn signal on, which is probably where the problem lies. However, I can't find the relay. Found the fuses for trailer lights but not the relay, though I hear it pinging when the right turn signal is on.
If it does turn out to be in the power module and you need to replace the module to fix then it would be possible to use a T-connector at your trucks taillight down to the 4 or 7 pin trailer connector. I have seen on the forum that the modules run $300 to replace. The T-connectors should have diodes that isolate and then connect the brake and turn signals to the trailer.
Thanks for the info but will be doing a lot of trailering this summer with two different trailers as well as a camper and don't want to risk overloading my truck lights. Decided to bite the bullet and consulted the top electrician at my Dodge dealer. His verdict: the trailer light relays are built into the TIPM on my 2005 Ram 2500 diesel, cannot be removed or replaced and the entire unit is "unflashable" meaning it can't be reset or updated. A new TIPM cost $377 in Denver plus an hour or so for labor to reprogram it. The good news, if there is any, is that the new modules have been updated to correct what is or was a very common problem in 2003-2006 Rams, namely the trailer tow left turn signal/brake relay output fries without blowing a fuse, necessitating replacement of the entire TIPM or, as weedahoe so rightly points out, a T-connect to the truck's taillights. The Dodge electrician points out, however, that even with diodes a T-connect could cause other problems, such as a "light out" warning on your dash or an overload in other circuits that would again fry the TIPM. I'm no expert, just passing along what I was told and since my Ram is the only wheels I got living where I do in the mountains, I have to be extra careful.