Battery for Frunk Release to store in bumper

[dtbaker61]

That is what I thought as well. 13.8v when I measured them last night. ???

that would actually concern me.... the terminal leads under that cover are not insulated or covered, and if they touch with voltage present.... big sparks and a blown fuse somewhere is likely. If you have power at those leads, I'd say you should have dealership service check it out!

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[SnBGC]

that would actually concern me.... the terminal leads under that cover are not insulated or covered, and if they touch with voltage present.... big sparks and a blown fuse somewhere is likely. If you have power at those leads, I'd say you should have dealership service check it out!

Agreed. They are fused but otherwise completely exposed. They were held securely into channels cast into the bumper but still.....stuff can happen.

I was mostly surprised by the 13.8 volt reading because I was expecting about 12.6 if any at all. That tells me the car was charging the LVB at the time I was checking the car (unplugged).

 

[louibluey]

Agreed. They are fused but otherwise completely exposed. They were held securely into channels cast into the bumper but still.....stuff can happen.

I was mostly surprised by the 13.8 volt reading because I was expecting about 12.6 if any at all. That tells me the car was charging the LVB at the time I was checking the car (unplugged).

Mine are dead, both MME power on and MME power off. Maybe your car is miswired, or the front trunk release relay is defective.

I am almost certain that Ford would not leave a ring lug 12V energized by design without a rubber cover.

Do you have a small 12V auto light bulb or something like that handy, maybe something that draws 1/2A or 1A? Just see if they are really powered, or if it is a phantom voltage indication (high impedance meter reading).

So here are some snapshots, those are presumably fuses F1 and F2. Because they are 20A fuses, that is some substantial wire.

 

[SnBGC]

Mine are dead, both MME power on and MME power off. Maybe your car is miswired, or the front trunk release relay is defective.

I am almost certain that Ford would not leave a ring lug 12V energized by design without a rubber cover.

Do you have a small 12V auto light bulb or something like that handy, maybe something that draws 1/2A or 1A? Just see if they are really powered, or if it is a phantom voltage indication (high impedance meter reading).

So here are some snapshots, those are presumably fuses F1 and F2. Because they are 20A fuses, that is some substantial wire.

I will check again. I am at work so I will have to borrow a meter from one of the techs.
Are your fuses okay?

 

[SnBGC]

Doesn't the diagram show those wires connected directly to the battery? Here are some more images that you can use for reference....

 

[DaMeatMan]

Guys these wires are not energized, they are simply there for you to supply power to the relay that pops the trunk. These are not connected to the vehicles low voltage battery.

The idea is that you supply power to these wires using a standard jumper cable, pop the hood, disconnect your jumper from these cables, then remove the plastic cover that hides the battery, then you can boost the dead battery with your jumpers.

Just to be clear, these are not energized cables that are left dangling with uninsulated ends.

 

[SnBGC]

And another view of C1100A that appears to point to a different spot....
????

 

[SnBGC]

Guys these wires are not energized, they are simply there for you to supply power to the relay that pops the trunk. These are not connected to the vehicles low voltage battery.

The idea is that you supply power to these wires using a standard jumper cable, pop the hood, disconnect your jumper from these cables, then remove the plastic cover that hides the battery, then you can boost the dead battery with your jumpers.

Just to be clear, these are not energized cables that are left dangling with uninsulated ends.

Yes. This is the belief on our end as well.
But, doesn't the wiring diagram say otherwise?
And why am I measuring voltage there?

 

[SnBGC]

Here are the other two relevant pages from this system....

 

[louibluey]

Yes. This is the belief on our end as well.
But, doesn't the wiring diagram say otherwise?
And why am I measuring voltage there?

I'm thinking that battery should have been the optional external 12V battery, if those are literally the red/black wires with the ring lugs.

Did not pull the 20A fuses, can check that later (It is chilly today, 20F).

I hear you about work, I need to do some work stuff too (soon), but when you get minute, could you look for that battery fuse box? And maybe check those two 5A fuses (I thought those were the new ones above, but they are 5A/5A in the BJB? (I need to be using my reading glasses, both 5A, not 3A))? (Thank you in advance!).

 

[louibluey]

yes! That is what I was thinking, the 5A fuses are to the left (off paper) in that first diagram.

I am going to study all this later. Is the battery fuse box near or on the 12V LVB? We need to be able to pull that F72 (assuming it is not one of those central fuse types bolted to the battery plus terminal distribution. If so, I might hesitate to disconnect it, unless it is dedicated to the frunk release system.)

 

[SnBGC]

yes! That is what I was thinking, the 5A fuses are to the left (off paper) in that first diagram.

I am going to study all this later. Is the battery fuse box near or on the 12V LVB? We need to be able to pull that F72 (assuming it is not one of those central fuse types bolted to the battery plus terminal distribution. If so, I might hesitate to disconnect it, unless it is dedicated to the frunk release system.)

Shows right on top of the LVB.....

 

[CHeil402]

I meant to respond sooner (I hate when work gets in the way). While this schematic doesn't show the complete picture, I do believe it can answer some questions about this process.

My previous understanding (and I think that of others based on discussions) is that there was a relay blocking out those bumper jumpers (that's a fun term... patent pending) that would only enable them when the car's 12 V battery was dead so a thief couldn't pop the hood and have unfettered access to your frunk shrimp. Therefore you would only need to apply enough power to activate the solenoid, like this...

Based on the Ford schematic, my current understanding is that the "Front Trunk Release Relay" isn't actually a true analog relay, but instead some intelligent device that requests the frunk to open. It is always powered by the 12 V battery from pin 6 (left VBATT). When you connect the bumper jumper power, it gets powered on pin 3 (right VBATT); HOWEVER, the logic is intelligent enough to only accept power from the bumper jumper IF AND ONLY IF the car's battery is below a certain threshold.

So basically, if the car's 12 V battery is dead, when you apply an external power source to the bumper jumpers it 'wakes up' the "Front Trunk Release Relay" which takes power from the bumper jumpers to activate the frunk release solenoid (not shown from what I can tell in the Ford schematic). More like this over-simplified drawing...

A few other notes... The bumper jumpers should NOT be energized by the car battery EVER... especially if they're connected as shown. This would definitely be a safety hazard if they were since the bumper jumpers aren't insulated... and even if they were, you can't expect everyone to put them back insulated after use.

The reason there are 20 A fuses on both leads of the bumper jumpers is likely for reverse polarity protection. If you connected the positive lead of the battery to the negative bumper jumper and the negative lead of the battery to the vehicle ground you've created a short-circuit which will trip the negative lead fuse.

The last question is what power source could you get away with on the bumper jumpers? I originally thought you might be able to get away with a 9V but since this is powering the "front trunk release relay" and not the solenoid directly, I think we have less options as there is some intelligence to this circuit. Not to mention that 9V batteries are terrible power sources. Your better bet to not have to worry about monitoring the health of your stored batteries would be to use an 8 battery AA holder to actually get 12 V. Something like this... https://www.amazon.com/Thicken-Battery-Holder-Standard-Connector/dp/B07WP1CYYW. And AA batteries are easier to get!

AA batteries are much more powerful than a 9V. We could likely test this by pulling fuse 72 and tricking the module into thinking the car battery is dead then applying the 12 V AA pack to the bumper jumpers. If I had my car I would test this and would measure the actual max current used to accomplish this.

Now that would get the frunk open, but if the car battery was actually dead (and not just because the DC/DC converter stopped recharging the 12 V battery) we might need a bigger source to jump the car... although probably not much more... see my other thoughts here:

https://www.macheforum.com/site/threads/ask-an-electrical-engineer.4307/post-132392

Sorry for the somewhat circular reference. I hope it doesn't break the internet.

UPDATE 3/25: Confirmed that 9V battery doesn't work. https://www.macheforum.com/site/thr...ease-9v-battery-does-not-work-12v-works.4774/ And 8 AA batteries do work! https://www.macheforum.com/site/thr...tery-does-not-work-12v-works.4774/post-141023

 

[SnBGC]

Based on the Ford schematic, my current understanding is that the "Front Trunk Release Relay" isn't actually a true analog relay, but instead some intelligent device that requests the frunk to open. It is always powered by the 12 V battery from pin 6 (left VBATT). When you connect the bumper jumper power, it gets powered on pin 3 (right VBATT); HOWEVER, the logic is intelligent enough to only accept power from the bumper jumper IF AND ONLY IF the car's battery is below a certain threshold.

So basically, if the car's 12 V battery is dead, when you apply an external power source to the bumper jumpers it 'wakes up' the "Front Trunk Release Relay" which takes power from the bumper jumpers to activate the frunk release solenoid (not shown from what I can tell in the Ford schematic). More like this over-simplified drawing...

Thanks.
Yes. That is how the operation is described in the manual. It says those wires in the front bumper only become active if the LVB voltage drops "below an established threshold".

 

[louibluey]

Shows right on top of the LVB.....

oh, I see you got the battery junction box. (thanks!)

The LVB is up closer to the windshield, but the LVB jump points are down lower as shown in the diagrams (so just the lower end of the back #2 ground cable, and the + jumper post).

It looks like the BJB is just the regular under the hood fuse box. That kind of makes sense, because there are so many fuses referenced to the BJB now. The only odd thing is that the fuse numbers from these Ford diagrams do not seem to match the fuse numbers in the MME supplementary manual.

So those two 5A fuses probably are the two I found in the fuse box listing of the supplementary manual.

Arrgg, I need to pull those panels again, and see how difficult it is to access those fuse blocks. I wish it was 40 degrees, sunny, but 20F and windy today! (and, some work now, only semi-retired )