Odd body control module fuse tap issue - 2024 Big Bend

[Spawn2031]

So let me preface this by saying I am a newbie to doing this kind of stuff but not technologically illiterate. So I had a pair of entertainment screens for my kids that I wanted to hardwire instead of using the cigarette lighter adapter. The install went fine, I used fuse no. 2 which controls power windows / DC inverter / Upfitter Switches and I thought everything was working normal until today.

I normally go to pickup my kids from school and sit in my Bronco with it Idling for about 30mins. I've been doing this for about 2 months now with her and I always have my gauges up in the MyView. While doing this I've never seen my oil temp get up past half on the gauges, usually around 190F. Today however (first time really driving it after the install) I noticed that the heater was blowing cold air while it was set at 75 and would only start blowing hot air if I cranked it up to 80. I also noticed that my oil temp was reading 207F. Both things that my Bronco doesn't normally do in these conditions.

I decided to remove the fuse tap and put the original 10 Amp fuse back in and everything went back to working as expected. I then relocated the fuse tap to no. 35 instead and everything continued to work as it always had. The reason I'm reporting this is because this was entirely unexpected and would like to know more about why this oddity would have happened. Is it possible tapping into this circuit somehow messed with thermostat or at least how the system was reading temps? I chose fuse no. 2 because many of the install videos I've watched for other interior lighting mods I plan to add say to use this particular fuse for taps, which now I'm worried about using in the future. Figured anyone else that's a noob at this stuff might benefit from NOT using this slot.

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[Brian_B]

I don't think your fuse location had anything to do with what you saw.

Oil Temps over 200F are normal, even up around 215-220F. The Bronco has an electric fan that is temperature controlled and it will let the oil temp get fairly high if that's the only thing it's driving. If you turn on the A/C (even with the heat running), it forces the fan on high to drive the condenser (since it shares the fan with the radiator) and you can "manually" cool your oil temp back down that way since it will overcool your oil and you'll go back through the thermostats. That said, I don't necessarily recommend doing that - the oil temp you saw was absolutely normal.

I've never seen the coolant gauge move though - it's always been around the middle (I don't know if there is a digital readout of it short of hooking up an ODB2 adapter), and I've never seen it budge a bit, but oil temps swing between 190-220 while at normal operating temp I've seen very commonly, and some people report seeing even higher.

That said, not sure why your heat was blowing cooler, but that may have been one of those automatic climate control oddities, as you said it did blow hot air once you cranked it to max. I don't have auto climate control, but apparently the sensor is down near the driver's side right leg? I've heard some people say resting their leg against the center console can be enough to cause it to do strange things, but I can't confirm it or try it out myself. The Bronco HVAC is maddening in general.

 

[Spawn2031]

Hey Brian thanks for the reply. Yeah, I wasn't overly concerned about the oild temp being reported at 207. I know that's in the normal range but since I've been doing this pattern for the past 2 months, I know that 190 is the norm for my Bronco under these conditions and Temps. That coupled with the fact that the hvac was blowing cold air with it being set at 75 when normally it would blow warm air at that same setting gave me reason to pause. Also, when I changed the fuse tap slot, not even 15 mins had passed from getting home so whatever was going on was certainly caused by the fuse tap being in that location. I just don't know why. It was like even though it was being told to blow at 75, it felt like blowing at low without the ac turned on. My guess us that the oil temp prolly was at the normal 190 but the gauge was misreporting it. I'll be doing this again tomorrow at nearly identical temperatures as conditions so I'm really curious to see what the oil temp says then. I know the hvac is working normal again.

 

[adam1991]

With modern cars, I figure something like this happening once is just one of those anomalies.

Put it back and see if you can repeat the behavior.

 

[Ducati1098]

Completely unrelated. That fuse has no barring on hvac operation or the oil temperature.

207 oil temperature is completely normal, and the hvac operation likely is too depending on multiple variables including humidity, ambient temperature, interior temperature, etc.

 

[Spawn2031]

Completely unrelated. That fuse has no barring on hvac operation or the oil temperature.

207 oil temperature is completely normal, and the hvac operation likely is too depending on multiple variables including humidity, ambient temperature, interior temperature, etc.

Ya, I'm aware. Which is why I'm posting this. Tapping into that fuse shouldn't have had any effect on this stuff at all but it did. With the fuse tap in a new location, I'm going to observe the gauges and hvac today and see if it returns to the pattern I'm used to seeing. If it does, I'm going to put the tap back in slot 2 and see if I can recreate the problem. If I can, then we'll know for sure.

 

[Ducati1098]

Ya, I'm aware. Which is why I'm posting this. Tapping into that fuse shouldn't have had any effect on this stuff at all but it did.

Okay. I'm not sure why you keep saying it had an affect though lol. It didn't, It was just a coincidence.
But if you want to keep looking for some correlation, good luck!

 

[Spawn2031]

Okay. I'm not sure why you keep saying it had an affect though lol. It didn't, It was just a coincidence.
But if you want to keep looking for some correlation, good luck!

I keep saying it had an effect because if you do Thing A and problem X shows up, then undo thing A and problem X immediately goes away, you have found a correlation even if there shouldn't be one. To be clear, I don't think that my oil temp actually was higher or that my hvac was malfunctioning. I'm leaning towards the actual Temps being misteported by the system. Also, I don't run my hvac system on auto. I control it manually so that removes a ton of variables there.

I may not be a mechanic but I've got tons of experience working with electronics and computer systems. I have seen more than my fair share of things that weren't supposed to happen but still happened anyway. Something measurable definitely happened here, I just don't know what but I'm going to see if I can confirm it later today and let y'all know if I could recreate it.

 

[derichio02]

I keep saying it had an effect because if you do Thing A and problem X shows up, then undo thing A and problem X immediately goes away, you have found a correlation even if there shouldn't be one. To be clear, I don't think that my oil temp actually was higher or that my hvac was malfunctioning. I'm leaning towards the actual Temps being misteported by the system. Also, I don't run my hvac system on auto. I control it manually so that removes a ton of variables there. The problem could have went away because the ambient temp changed at your last location by the time you swapped the fuse tap. All is takes is a cloud to block the sun.

I may not be a mechanic but I've got tons of experience working with electronics and computer systems. I have seen more than my fair share of things that weren't supposed to happen but still happened anyway. Something measurable definitely happened here, I just don't know what but I'm going to see if I can confirm it later today and let y'all know if I could recreate it.

What Ducati is saying is correct and I don’t think you would be able to recreate the exact scenario as it would depend on multiple variables such as interior and exterior ambient temp, humidity, elevation, etc. All of those variables could have an adverse effect on your experience. Setting my temp to 75 degrees on Auto almost turns my HVAC off sometimes and at other times it will blow cold or warm but this all depends on the variables I mentioned above. Even if you found a slight correlation it could be debunked because of those external variables.

If what you have right now works I wouldn’t spend time chasing down anything else.

 

[Spawn2031]

What Ducati is saying is correct and I don’t think you would be able to recreate the exact scenario as it would depend on multiple variables such as interior and exterior ambient temp, humidity, elevation, etc. All of those variables could have an adverse effect on your experience. Setting my temp to 75 degrees on Auto almost turns my HVAC off sometimes and at other times it will blow cold or warm but this all depends on the variables I mentioned above. Even if you found a slight correlation it could be debunked because of those external variables.

If what you have right now works I wouldn’t spend time chasing down anything else.

I appreciate the input! One thing that I should have put in the original post is that I don't use the auto setting on the hvac. I just usually keep it at 75 and just turn the fan up or down or just off. If I was using the auto setting then yeah, way too many variables to co sider there. I'm still gonna chase it once I get back from picking up my kiddos. I hate loose ends and it'll take no time at all to try. I've got another couple things I wanna add in the future that will require me to use that no. 2 slot if I add them all so I wanna get out ahead of this thing... if it is a thing. I honestly hope I change things around again and find that it had nothing to do with that fuse tap but from what I saw last night, it does. I'll be trying it in about 3 hrs and will report back.

 

[Spawn2031]

Alright... so, identical weather today compared to yesterday. First thing, after idling for 30mins like usual, oil temp never went past 190 as usual and Hvac running as normal, 75 blowing warm air with no automatic controls on.

When I got home, I put the fuse tap back in slot 2. Hvac immediately started blowing cold air with all the same settings. Shut down, removed the fuse tap again and it's back to normal. I repeated this test one more time with the exact same results.

So, something about this fuse tap in slot 2 is definitely causing oddities and is repeatable. The only question is why. If none of you have experienced something like this on a '24 Big Bend with this slot then the problem has to be something with the fuse tap I would imagine but it works fine in slot 35. The only difference would be the size fuse that's going in the slot for the original circuit. I'm using a 5amp fuse for the new circuit so when in slot 2, the fuses are 10amp / 5 Amp. In slot 35 its 5 Amp / 5 Amp. I've been told that shouldn't matter but it's the only thing that's different.

 

[GTTom]

Just curious. I know you said you have tons of experience in electronics but did you check the fuse tap is in the proper orientation? The left side of a fuse tap is typically the hot leg and the right side for the load or accessory you are powering. If you inserted the fuse tap facing the wrong way it may affect the way you power the circuit. if I remember correctly when I installed my dash cam the right side of the fuses in in the fuse box is the hot side so the Left side should be going to the load.

 

[Spawn2031]

Just curious. I know you said you have tons of experience in electronics but did you check the fuse tap is in the proper orientation? The left side of a fuse tap is typically the hot leg and the right side for the load or accessory you are powering. If you inserted the fuse tap facing the wrong way it may affect the way you power the circuit. if I remember correctly when I installed my dash cam the right side of the fuses in in the fuse box is the hot side so the Left side should be going to the load.

Yeah, that was one of the first things I checked to make sure I didn't miss something small. Thanks for asking though!

 

[Bschurr]

Today’s modern electronics are increasingly becoming sensitive to adjacent interference of EMF & voltage drop etc.

I am not an experienced electrical nerd on the internet but I do run a AV firm.

 

[Brian_B]

I don't use the auto setting on the hvac. I just usually keep it at 75

That pretty much is exactly using the Auto on the HVAC. You may have overridden the fan speed, but it’s still automatically controlling the heater blend and A/C to adjust to your temp.

It’s not the same thing as the peasant blue<->red dial that just sticks the heater blend at wherever you turn the dial.

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