Well, that didn't work. Best practice for installing electrical accessories.

[Robert_C]

Yesterday I was attempting to install my Ham radio, GMRS, and APRS radio beacon in my maverick hybrid.

I ran a wire from Fuse #3, the unused switched fuse. That went to a relay. The relay went from the positive terminal of the battery to the distribution block. The negative side was connected to chassis ground.

When placed in Accessory, the vehicle immediately started flashing various error messages. It was clear that this was not the way.


Seeing as this didn't work, I am considering going straight to the ground lug on the battery, bypassing the built in power checks.

Is this what others are doing?

Is there a better way?

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[Mabcim]

I use fuse 3 for three devices (an Arduino board, a Ford auto dimming mirror, and a Homelink garage opener) on my ‘25 Ecoboost and have had no issues. I ran just the Arduino board on my ‘22 Eco for 2.5 yrs with no issue either.

Being connected to a relay, you should be fine.

The only things I can think of for you to check are:
1. make sure the fuse tap isn’t backwards (not that it should cause the issue even if it was)
2. test the relay (out of the vehicle) to make sure it isn’t shorting out internally
3. Confirm the battery ground is the same as the fuse box ground. I haven’t done anything on a Hybrid, so not sure if the inside 12v runs the electrics or just is used to start the vehicle.

 

[scharris99]

I'd definitely put a fuse between the battery & the relay! Not sure what you are using for various ground locations, but I'd use an existing factory location. When I install anything audio I run my own ground cable back to the battery in parallel with my power cable, both a gauge larger than required.

 

[colinl]

When I install anything audio I run my own ground cable back to the battery in parallel with my power cable, both a gauge larger than required.

I used to do that years ago, but in the current era of battery monitoring systems, I do not ground to the battery per Ford (and probably everyone else's) best practices.

the reason is that the BMS (which I believe is a combination volt and ammeter) may not read current draw correctly if you have anything else on the negative terminal. however, if you make your own short ground properly, it costs a lot less in cabling and will be cleaner than re-using a factory ground*, and it'll ensure the BMS is working properly as well as Ford battery monitoring can be expected to work LOL.

*in particular do not re-use a ground with a window motor or brake controller on it. they're noisy.

 

[Robert_C]

A bit more information, Fuse 3 and Fuse 20 are both also powering the dash cam with no real problems.

For the ground, I went to the chassis ground on the end of the negative power cable. I just unbolted it and put the ring connector under the bolt. I did this because several people here have said

I misstated my initial description. As long as there was no load at all on the distribution block, it worked and metered just fine (except that the voltage did seem to be a bit low at 11.8Vdc). It was 0Vdc when the accessory was off, and close to 12Vdc when the accessory circuit was on.

The error condition occurred when there was any load at all on the distribution block. This was even the small load caused by the audio mixer (There are four audio inputs into one speaker; this calls for a mixer).

The guess by the service people at the local Ford dealer was that the car is looking at what it knows is on, in that case, nothing but the radio, and what is being drawn, through the sensor on the ground cable.

It saw a mismatch and started rapidly cycling the accessory circuit, causing the buzzing sound I heard near the relay, which sounded like a priming pump. What seems odd about this explanation is that there is no similar issue caused by the dash cam.

Again, the service person's explanation. His guess was that there was some wiggle room in the circuit power draw comparison, and the dash cam was nearing the edge of that space, so that any additional load was causing the error. Bear in mind, he did not use the word "Guess" as he said what he thought was going on.

The suggestion was to connect the ground for my distribution block directly to the battery, bypassing the current sensor on the ground cable. The thought was that the relay would keep the system from being left on, thus making it a safe way to wire the circuit.

I will give it a try soon. Today I have other stuff that I ned to do.

 

[Robert_C]

I'd definitely put a fuse between the battery & the relay!

There is a fuse there. I just had trouble making my drawing in Fritzing, or even TinkerCAD.

 

[MetalsGeek]

Bypassing the BMS Hall FX sensor on the ground side of the battery will probably create some grief down the road, so I would definitely use the chassis for all your grounding needs. Conceptually, your schematic looks perfect, although a fuse on the main line is of course appropriate. I've done the same thing but powered the relay coil from the switched accessory power at the lighter jack.
A 1N4004 diode across the relay coil (with cathode band to + side of course) will suppress the transients produced by the coil when power is switched off. Sometimes this can help but probably not needed here.

 

[colinl]

The suggestion was to connect the ground for my distribution block directly to the battery, bypassing the current sensor on the ground cable. The thought was that the relay would keep the system from being left on, thus making it a safe way to wire the circuit.

The very first thing I'd do is ensure than the remote power-on wire - at least I assume that's what you have tapped to fuse #3 - is not swapped with the +12V battery connection.

Then, having checked that, I would instead put the inline fuse or circuit breaker in between the 12V relay and battery +.

 

[Mabcim]

Again, the service person's explanation. His guess was that there was some wiggle room in the circuit power draw comparison, and the dash cam was nearing the edge of that space, so that any additional load was causing the error. Bear in mind, he did not use the word "Guess" as he said what he thought was going on.

That would be the next thing to check, to see how much current draw you have on the fuse.
I know wires coming directly from the BCM can only handle so much current, which is why relays are used for hi draw things. However, I wouldn‘t think a fused line would get monitored, but maybe they do. Can’t remember is the factory fuse is 5 or 10, but 5 amps would be a lot. But if it is monitored, it could look for less.
Your dash cam should have an Amp rating listed. The relay should, but that be harder to find. The best thing to measure what they are both actually doing.

 

[FeatheredMonkey]

I use fuse 3 for three devices (an Arduino board, a Ford auto dimming mirror, and a Homelink garage opener) on my ‘25 Ecoboost and have had no issues. I ran just the Arduino board on my ‘22 Eco for 2.5 yrs with no issue either.

Being connected to a relay, you should be fine.

The only things I can think of for you to check are:
1. make sure the fuse tap isn’t backwards (not that it should cause the issue even if it was)
2. test the relay (out of the vehicle) to make sure it isn’t shorting out internally
3. Confirm the battery ground is the same as the fuse box ground. I haven’t done anything on a Hybrid, so not sure if the inside 12v runs the electrics or just is used to start the vehicle.

Can I ask how you ran multiple devices off of the same fuse? I’m about to install an auto dimming mirror (with homelink) and a dashcam with the thought of using fuses 1/2 for the camera and 3 for the mirror. Never considered using just the one fuse.

 

[BlueSpec1]

I'm using F1/F2 fuse tap for switched power for Dash Cam Buck Converter and my CCM Radar Module.
Crimped their wires into one QC from that fuse tap.

 

[Mabcim]

Can I ask how you ran multiple devices off of the same fuse? I’m about to install an auto dimming mirror (with homelink) and a dashcam with the thought of using fuses 1/2 for the camera and 3 for the mirror. Never considered using just the one fuse.

I had 1 wire crimped on the fuse tape when I had it in my ‘22. When I needed to also add the mirror to it on my ‘25, I just stripped a little of the fuse wire (right in the middle of the wire) and soldered to it. 3M makes connectors to make it easier, I just wanted to be sure it was fully secure. Something like this: https://www.grainger.com/product/4Y...3P-BFlx4GXy-Lca06alHF4aaw5cQZLK0aAmZTEALw_wcB

 

[AutobahnSHO]

Can I ask how you ran multiple devices off of the same fuse? I’m about to install an auto dimming mirror (with homelink) and a dashcam with the thought of using fuses 1/2 for the camera and 3 for the mirror. Never considered using just the one fuse.

My dashcam and homelink mirror are on one fuse, no issues. They're pretty low current draw compared to what OP wants to run.

 

[Mavster Mechanic]

Yesterday I was attempting to install my Ham radio, GMRS, and APRS radio beacon in my maverick hybrid.

I ran a wire from Fuse #3, the unused switched fuse. That went to a relay. The relay went from the positive terminal of the battery to the distribution block. The negative side was connected to chassis ground.

When placed in Accessory, the vehicle immediately started flashing various error messages. It was clear that this was not the way.


Seeing as this didn't work, I am considering going straight to the ground lug on the battery, bypassing the built in power checks.

Is this what others are doing?

Is there a better way?

Fuse #3 is not unused in mine.

It runs the Co-Pilot 360.
It puts warnings on the screen and all Co-Pilot 360 features are disabled if this fuse is blown or removed.

I'm probably still going to use a 2-way tap on this though.

After thinking on it, I kind of like the fact there will be instant, in your face warnings if the fuse ever blows.

I'm just using it as the signal wire to a relay so I have switched power.

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