How to determine switched or unswitched fuses in footwell fuse box

[Bossdog]

What am I doing wrong?
I'm using a multimeter to check fuses in the foot well fuse box.
Meter is working properly, measuring Volts DC
Probe tips are small enough to get into the Microfuse openings on the fuse body
I press START button (No foot on brake pedal) to activate accessory power. Radio and climate control come on
I'm still not getting any voltage readings.
Fuse #24, 20 amp, power locks, should be active all the time, not switched, no reading
So, I must be doing something wrong.
Any help is appreciated.

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[pt's21]

If you're checking across the fuse, and it is not blown, the meter will not show voltage.

One probe on a nut, bolt, or screw that's into metal (chassis - battery negative), then probe fuses with the other probe.

 

[NGOT8R]

Fuses #23 and #35 in my 2019 Bullitt are switched 12V sources. I use both to power aftermarket accessories using a Micro II add-a-fuse.

 

[Traffic22]

Might be bad ground. My probe didn’t like any painted surfaces when I was checking, look for an uncoated bolt. There are a couple obvious grounds near the footwell fuse box, they work well.

 

[Bossdog]

Thanks everyone, much appreciated. I have no skills when it comes to electrical.

 

[GTP]

There is a 10mm bolt above the fusebox. I use a ring terminal under it for dashcam ground and for my DIY rear diff pump ground.

Comment on checking across the two probe spots on a fuse...
When the fuse is good, you are essentially probing the same spot in the circuit. The "potential difference" (i.e. voltage) is therefore zero and that is why a meter won't read that way. As stated previously, you have to probe the fuse and a ground point.

Also, I found that the "source" (12v) end of the fuses are towards the front of the car, and the "load" end of the fuses are towards the rear. Therefore, when adding a "tap-a-fuse" device, it is best for the pigtail wire to face towards the rear of the car.

IIRC, fuse #2 is always hot, and fuses 23 and 35 are switched. I could not find any other switched fuses.

 

[boB]

One catch about using a meter to check for power is the typical 10 Mohm impedance can show "phantom" voltage. For a simple voltage check I place a 1K or 100 ohm resistor across the meter leads. Another low-tech option is a LED or even an old-school test lamp.

 

[Bossdog]

Fuses #23 and #35 in my 2019 Bullitt are switched 12V sources. I use both to power aftermarket accessories using a Micro II add-a-fuse.

In my 2019 manual, Fuse 22 is "Spare (not used)". #23 is "switches Power windows / rear-view mirror". actual observation supports that, 22 has a 5 amp fuse as the manual indicates.

I am assuming there is no need to put the 5 amp fuse back into the "add-a-fuse" when added to #23 Spare-not used, is that correct?

Also, it looks like 22 is not a Micro 2 size fuse it looks like the larger ACT/ATO size fuse

 

[NGOT8R]

In my 2019 manual, Fuse 22 is "Spare (not used)". #23 is "switches Power windows / rear-view mirror". actual observation supports that, 22 has a 5 amp fuse as the manual indicates.

I am assuming there is no need to put the 5 amp fuse back into the "add-a-fuse" when added to #23 Spare-not used, is that correct?

Also, it looks like 35 is not a Micro 2 size fuse it looks like the larger ACT/ATO size fuse

Stby for a sec and I’ll go take a pic of mine for you.

 

[NGOT8R]

@Bossdog here are pics of #23 and #35 in my passenger side interior fuse panel. I use 10A fuses in both slots of my add-a-fuse for slot #23 and 10A/5A fuses in my slot #35 add-a-fuse.

 

[Bossdog]

@NGOT8R Mine looks the same. I'll be using 35 as in your photo.
Yes, I see 23 in your photo, thanks but my manual says this is used for switches, not a spare. it surely could be used for accessories as well.

 

[NGOT8R]

@NGOT8R Mine looks the same. I'll be using 35 as in your photo.
Yes, I see 23 in your photo, thanks but my manual says this is used for switches, not a spare

I gotcha. Well at least you now know that you can use both slots, should you need another down the road for another accessory. I’ve been using both slots for a very long time with absolutely no issues at all.

 

[GTP]

@Bossdog here are pics of #23 and #35 in my passenger side interior fuse panel. I use 10A fuses in both slots of my add-a-fuse for slot #23 and 10A/5A fuses in my slot #35 add-a-fuse.

Without sketching out a circuit, I'm not convinced that your added device is truly fused when you run the add-a-fuse wire forward instead of in the rearward direction. I recall testing for voltages with/without fuses in place, to verify that the load is at the right-hand side of the fusebox as you face it.

IOW, if the main fuse blew, then your added device will still be powered even if its add-a-fuse blew.

I always run the wire facing the rear, and sometimes it's tricky to get clearance for it.

 

[SheepDog]

https://www.amazon.com/Power-Probe-...64&keywords=power+probe&qid=1712341842&sr=8-5

 

[NGOT8R]

Without sketching out a circuit, I'm not convinced that your added device is truly fused when you run the add-a-fuse wire forward instead of in the rearward direction. I recall testing for voltages with/without fuses in place, to verify that the load is at the right-hand side of the fusebox as you face it.

IOW, if the main fuse blew, then your added device will still be powered even if its add-a-fuse blew.

I always run the wire facing the rear, and sometimes it's tricky to get clearance for it.

I’ll double check which side is the load side again soon, but I’m pretty sure I did this when I first installed them.

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