Which leg of fuse connects to battery

I’m trying to tap into any fuse that comes on after ignition, to hard wire a dash cam on this A3 mk3 Jetta TDI. Which side of the fuse is connected to the load and not to the battery??

Remove the fuse and the terminal that still has power comes from the battery.

Dont do it that way, go into behind your radio, (i think its the yellow solid) test with volt meter to confirm, and hook up a 30/40 relay and a 14g THHN or K wire from the battery to the relay. now run a fuse to whatever device you want. you can run LOTS of things off this relay and your cars electronics wont suffer.

Things that will happen once you start pulling current from a device on the ignition directly include*
*poor audio quality
*flickering lights
*over worked old wires that are brittle
*high pitch whining over the speakers regardless of radio on or off


What dash cams you running?
Black Vue is the best. 2 channel front and back.

a tip
take that stuff out of the car when parked. you will end up with a broken window and all your stuff stolen and the cams gone as well and you wont have the footage to prove it.

IMHO the best cash cams are the battery operated ones that go inplace of your rear view mirror. they come off easily and you can charge USB and they last like 8 hours and for longer trips you can plug them in directly.

Food for thought

to answer you directly, go get a volt meter and figure it out.

Thanks guys these are solid tips. Was asking because while my electric circuits are all working, pulling the fuse and looking for 12V with the meter red probe (black probe on chassis ground) was failing consistently to find any 12V, I think my probes are not compatible with just sticking into these fuse holders, it doesn’t actually contact my probe?! So I thought this is surely an answer everyone knows by now on these 20 yr old mk3’s, which rail is hot, upper or lower.

I’ll go back and try to get a much closer look at probe vs fuse socket and see why it’s not making contact with my probe!!

About the dashcam: it’s a Chinese low quality cam false advertising, was described as 1080p mp4 video compression format, in fact it’s just 720p upscaled to 1080p, mpeg2 video format files so large you get way less recording time per GB!! Will upgrade to a decent cam with high quality video and mp4 compression as soon as I do these:
1. Complete the upgrade to LED lights interior and exterior, plus add DIY LED fog lights,
3. Add security system alarm, sensors, with cloud connection to upload dashcam video to a safe secure internet cloud location that will survive any vehicle accident, vandalism, theft, etc.

make sure your probe is grounded. never EVER use the chasis ground for anything. always run a ground wire where possible.
UNLESS you do "the big three" its a ground wire upgrade and alternator upgrade on the charge wire.

putting that much security into a car that never needed it before!.

check your auto policy. 99% chance nothing of this nature is covered at all.
Most policies classify aftermarket things as "takes power from the cars system" and was not put there my the OEM" these items are not covered under your auto policy whatsoever. And to make it worse, theft caused by aftermarket items makes the damages not covered as well. Case in point, have a aftermarket dash cam, crackhead breaks in and takes it, busting a window in the process. You try and claim the window as covered by your policy and it will be denied. its total BS. READ your policy and talk with your local agency and get IN writing anything that they say otherwise, because the ppl at these places dont even read them, this is for lawyers to read.
And whats worse, most states now do not take dash cam footage as evidence due to the EASE of faking a video. Check your local laws about this too. In MD, its not evidence and will not hold up in court unless its a certified encrypted device that costs tens of thousands of retarded dollars.
So out of court of auto policy, regardless, its basically a novelty to have to take that with a grain of salt.

anyways, ive been down this road, IMHO your wasting your money. its fun to get crazy moments on camera and what not and thats why i say just get a gopro and stick it to the inside of the window. they make that part to do this. take it off when your not in the car.

So you're wanting switched power for your dash cam? That would be anything concerned with circuit 15.

The easy way to do this is to find a fuse for circuit 15 and tap into that fuse by going to the small junction blocks above the fuse panel that has group connections for that fuse.

Don't do any patching in behind the radio or any other splicing into existing wires. Go to your wiring diagrams for ignition and look at fuses that are downstream on circuit 15 and take your pick. Here, I've gotten them already, they are:

Fuses 4, 5 and 9 are run power fuses
Fuses 6, 13, 14, 16 and 17 are start/run power fuses

I would pick a junction block served by fuse 4, 5 or 9. I would prefer my camera not try and power up while the car is being started. It makes more sense to have the camera start up once the engine is running. Remember, if the startup is not successful the camera will shut down and reboot, let's avoid that situation.

One of the run power fuses above is connected to harness D. My personal preference would be to see where the wire from harness D position 7 is going. IIRC that connects to a junction block providing switched run power to various things. D/07 is supposed to provide run power to ABS module but if you don't have it then the connection would be open and available. Harness D is a misc equipment harness so there should be lots of options there IIRC.

The reason I don't tap into electrics out at the devices is because in some cases that can have adverse consequences. Case in point on Mk3 cars non-factory stereos can cause problems with OBD2 connections with various tools like VAG-Com etc. That's not a situation that's desirable in my book.

Further, splicing into connections out there and not doing a thorough job of sealing the connection can cause shorts with the metal dash substructure and that's also not good. In fact that can cause dash fires and all sorts of unresolvable problems.

Additionally, I stay away from connections that splice into the fuse mounting directly, since they can open the slot of the fuse holder up larger than it should be. I had to replace a fuse box in a Mk3 once because of one of those fuse taps. They are junk and a bad idea.

Critical fuse information is here at the bottom of the page.

Best practice is to go get your power where the factory equipment gets it.

Steve