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Discussion Starter #1
Morning, y'all :D

I have a Promaster 3500 I use as a lawn care work vehicle. It was fitted with a dovetail direct from the dealer.

The joy this van brings me is unfathomable.

I have to replace my second BCM in 50k miles - YAY!

Thanks for allowing me to be a member. Much abliged.

-Matt
 

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Welcome Matt!

I'm just down the road in Maryville. What do you mean by a "dovetail"? I'm assuming some sort of ramp. Have any pictures you'd like to share?
 

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Matt,
Welcome. If you have had issues with your van we appreciate a straightforward explain. Isn’t FCA fixing it? Symptoms? The BCM has been very trouble free.
 

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Bcm?
 

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Discussion Starter #7
Welcome Matt!

I'm just down the road in Maryville. What do you mean by a "dovetail"? I'm assuming some sort of ramp. Have any pictures you'd like to share?
My east TN brethren!


Untitled-1.jpg


That rear of the truck was put on the by the dealer ship.

In terms of the BCM, I keep getting errors on the dash that the tail and reverse lights aren't working, and sure enough, they're not. In fact, one running light in rear won't even turn off when the truck is turned off. The windows don't work either.

I took the truck back to the dealership and they said it was the BCM. Trucks out of warranty, so it was around ~800 to have it replaced and reprogrammed.

5 months later, same issue. Dealership saying it will be ~800 to have it replaced and reprogrammed. Offering no other insight as to why it's happening or if it relates to the dovetail (they installed the dovetail). The only piece of information the dealership gave me was - "well the promaster does have some electrical gremlins from time to time"

I've ohmed out all the wires running to the lights and there are no obvious shorts. I even followed the wires back towards the cab as far as I could keep up and saw no obvious issues with wiring. I have no other guesses as to what the issue is.

The struggle is real!
 

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Just a SWAG (wild guess) on my part, but I would suspect they may have wired a load directly to the BCM that requires too much current and should have gone through a relay instead (or a different type of relay). Perhaps the "dovetail's" manufacturer can share additional information that the dealer won't or doesn't know.

I've reviewed a couple of my son's car-modification projects and it's surprising how involved a modern car's electrical system is. There are plenty of opportunities to screw up. Again, just a guess since I don't know what your dovetail involves.
 

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I concur. If I were going to wire that tail I would match each light’s wiring to the origional even using the same bulbs. I don’t know why these are so fussy but my Dad's Mercedes gave us issues until I went to a dealership and they said “Did you get our bulbs?” when the rears burnt out. I told them that couldn’t be it but bought 3 or 4 bulbs at their ridiculous price and we never had another problem and that was a pre-BCM car!
 

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Discussion Starter #10
Just a SWAG (wild guess) on my part, but I would suspect they may have wired a load directly to the BCM that requires too much current and should have gone through a relay instead (or a different type of relay). Perhaps the "dovetail's" manufacturer can share additional information that the dealer won't or doesn't know.

I've reviewed a couple of my son's car-modification projects and it's surprising how involved a modern car's electrical system is. There are plenty of opportunities to screw up. Again, just a guess since I don't know what your dovetail involves.
I think you're onto something. The issues started when the two of the lights failed and they were replaced with the same style light from autozone.... time to do some digging...
 

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The dovetail looks like it is using the standard trailer 3 wire lights. Are these LED? The body builder guide for your truck clearly states that they can't be LED.


The OEM 12 wire connector should be located at the left rear of the frame. I'd disconnect it, and wire in a pair of stop,turn,tail trailer lights to test with eliminating the dovetail completely.

Go to https://www.ramtrucks.com/ram-commercial/body-builders-guide.html and pick 2017 (2016 and earlier only work with Internet Explorer). After chooisng 2017, click on the picture of the Promaster, then scroll down and click on "Electrical Wiring Information". When the list below pops up, click on Exterior Lighting Modifications / LED"

The 4 page document that pops up will have a few tips and tricks, as well as the wiring diagram for the 12 wire connector.


If one of your lights stays on with the truck off, I suspect that the dealer swapped a positive and negative somewhere, AND that positive is shorted out somewhere along the dovetail, or maybe where the wire gets flexed every time you open/close the dovetail.

Good luck!
 

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Vast majority of BCM's are replaced by techs unable to properly troubleshoot and diagnose issues with today's vehicles. Previous comments are likely spot on, go back check lights, wiring and load for the real problem. Oh and find another shop if they can't or won't give you details on how they came up with the diagnosis as BCM's and similar devices rarely just fail. There is always a reason for the failure...
 
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