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Hello, I am a newb on this forum, so I apologize in advance if this has already been answered. I've been searching for a while now... For my 2015 F150 2.7 EB. I am dealing with a bad relay connection for the Engine Cooling Fan Relay 3 – Located at BJB Position #104 (in the engine bay). Symptom is the relay has burnt up twice. The first time I thought it was just a bad relay, and the socket on the BJB was just slightly discolored. The second time, the socket on the BJB is totally burnt and melted. I am nearly 100% sure this is not a problem with the fan motor being bad and drawing too much current, and there is no sign of water intrusion or any other damage. My theory is that the relay socket wasn't making good contact to begin with, and the resistance caused it to overheat, eventually damaging the first relay. After replacing the relay, the problem continued and only got worse until it got to this point.
I need to get in there to repair the socket (replace the damaged contacts), or most likely, tap into the wiring inside the BJB and install a new, external socket.
The general location is shown here circled in green (relay has already been removed): Affected area, circled in green BJB Position #104 for Engine Cooling Fan Relay 3
Can I just remove that one affected block of relay sockets that is circled in green above? It appears to be modular, and I see what look like clips, but am not sure if it is possible or if special tools are needed.
The last thing I want to do is screw up the BJB and cause bigger (more expensive) issues, so I am hoping someone has done this before and can give me some tips.
I have found similar information for older models, but nothing for the 2015-2017 models (I believe the BJB changed in 2018)
You won't be able to buy just the parts that need to be changed. That part of the BJB can be disassembled and repaired, although I have not done that. You would have to buy a BJB from a salvage yard to get the parts. It might make sense to just buy a new BJB.
Yea you have some investigation to do to find the cause first. I think your poor connection theory is sound. The post you linked is LONG and I'm not going through it all. First you need to get the relay / fuse box out to find out. From the pics it looks like sections snap onto each other, are there bolts or screws holding it down? Probably you would find a large pin connector on the back or bottom? If you can identify the wires in that connector it would be prudent to measure wire resistance at the fan connector too. You could always go to a scrap yard and find a wreck to experiment, operate on or possibly obtain parts before you dig into your own.
Thanks for the replies. That is all good info and I appreciate it. To be clear, what I am looking for here is if anyone has hands-on experience or knows of information on how to go about disassembling the BJB (or pulling that one section out). I'm just not sure how to go about getting it open.
Last edited by carterman; Aug 7, 2022 at 08:33 PM.
Not the most elegant solution but you could do so some bypass surgery. If those other open sockets are not being used perhaps from the back side you could rewire the burned-out socket to use one of them.
@carterman did you ever complete this project ? I bought a used BJB myself, can't figure out how to disassemble that thing to save my life.
Hey @TXFRDOwner I gave up on trying to disassemble it. The modules look like they should come apart, but the fit is so tight they may as well be one piece. The slots that join together have ramp-like protrusions that lock them together. There isn't a release mechanism that I could find. I believe they simply cause an extreme friction fit once assembled.
Even on the junkyard one I bought to experiment with, I could not get them to separate, even eventually trying a hammer on it! So yeah, there's no way I can see to extract one of those modules with in-place BJB in the truck.
You may be able to lift the whole thing out of the shell, as it clips into the shell on the sides, but you'd have to have enough slack in the several wiring bundles going into the BJB and that may not be possible. Also, the inside is an absolute rat's nest of wires. So getting to the connector that needs to be repaired may be tough even if you manage to separate things. This is what it looks like on the inside!
I did find that you can easily pop off the white tops of the sockets, allowing close access to the top of the connectors inside. I figure if worse comes to worse, I could just cut away the plastic from the top to get access to the connector, pull it up and splice into the wire, and extend it and remote-mount the relay.
But it didn't come to that (not yet at least). I did confirm that the receptacle for that relay connector was loose by inserting a 1/4 spade connector into it and comparing the friction of the fit with another one that did not have a problem. The spade inserted and pulled out with almost zero friction in the bad receptacle, whereas there was some friction in a good receptacle. So what I did was to put a thick pad of solder on the relay spade connector to make it thicker, so it fits tight in the receptacle.
I am hoping that this is a good fix and will reduce the resistance at that connection. I figure if it does overheat again, the solder will melt and hopefully then flow and make a good connection.
We are just starting to get really hot weather here in AZ... it is going to be over 110 degrees all week here, so I should know in a week or so if this fix worked. (During the cooler months, the fans don't run on high, so the problem has only happened during hot weather when they run non-stop).
Good luck with your fix! Hope this helps.
Last edited by carterman; Jul 3, 2023 at 02:44 PM.
Hey @TXFRDOwner I gave up on trying to disassemble it. The modules look like they should come apart, but the fit is so tight they may as well be one piece. The slots that join together have ramp-like protrusions that lock them together. There isn't a release mechanism that I could find. I believe they simply cause an extreme friction fit once assembled.
Even on the junkyard one I bought to experiment with, I could not get them to separate, even eventually trying a hammer on it! So yeah, there's no way I can see to extract one of those modules with in-place BJB in the truck.
You may be able to lift the whole thing out of the shell, as it clips into the shell on the sides, but you'd have to have enough slack in the several wiring bundles going into the BJB and that may not be possible. Also, the inside is an absolute rat's nest of wires. So getting to the connector that needs to be repaired may be tough even if you manage to separate things. This is what it looks like on the inside!
I did find that you can easily pop off the white tops of the sockets, allowing close access to the top of the connectors inside. I figure if worse comes to worse, I could just cut away the plastic from the top to get access to the connector, pull it up and splice into the wire, and extend it and remote-mount the relay.
But it didn't come to that (not yet at least). I did confirm that the receptacle for that relay connector was loose by inserting a 1/4 spade connector into it and comparing the friction of the fit with another one that did not have a problem. The spade inserted and pulled out with almost zero friction in the bad receptacle, whereas there was some friction in a good receptacle. So what I did was to put a thick pad of solder on the relay spade connector to make it thicker, so it fits tight in the receptacle.
I am hoping that this is a good fix and will reduce the resistance at that connection. I figure if it does overheat again, the solder will melt and hopefully then flow and make a good connection.
We are just starting to get really hot weather here in AZ... it is going to be over 110 degrees all week here, so I should know in a week or so if this fix worked. (During the cooler months, the fans don't run on high, so the problem has only happened during hot weather when they run non-stop).
Good luck with your fix! Hope this helps.
It's good to know I'm not crazy LOL. I appreciate you sharing the pictures and your experience with this project.
If I discover any new information for the disassembly process, I'll be sure to report back and share it.
Damaged Relay Socket in BJB
