TheSamba.com :: View topic - Tapping into illumination, parking brake, and reverse circuits

Sun May 26, 2024 5:10 pm

While upgrading my 2000 Eurovan camper radio, I needed to find 3 additional circuits which are not part of the stock VW radio wiring harness:

1. Reverse/Backup light circuit (+12V when the transmission is in Reverse)
2. non-dimming illumination circuit (+12V when the headlights are on)
3. Parking brake circuit (connects to ground (???) when the parking brake is on)

I did a bunch of research, poked around on the fuse box, and even opened up my shifter console, but I did not come up with good answers for any of these.

What I did:

1. Reverse : tap into the brake light circuit in the right rear tail lamp and run a wire (about 30' length) to the radio.
2. Non-dimming illumination: tap into the headlight switch
3. Parking brake: I gave up.

(See here https://www.thesamba.com/vw/forum/viewtopic.php?t=792269)

Are there a better solutions? Can you find these circuits on the fusebox? Given the parking brake turns off the DRL (Daytime Running Lights) - maybe the parking brake circuit is also found on the headlight switch?

Sun May 26, 2024 5:33 pm

When I put in the back up camera for my radio set up, the aftermarket green wire indicated it hooked up to the "Parking Brake (-)" but this made no sense. I contacted Crutchfield and they said there would be 1 wire (green with grey strip) to tap into at the park brake. I tried to tell them they were wrong, but they kept repeating the same instructions even though I kept telling them there were 2 wires at the park brake, see pic. If you tap into the (-) side, that would be like tapping into the ground which tells you nothing about the state of the park brake. You must tap into the (+) side.

I removed the 2 center consols and routed the wire under the carpet and tapped into the "Parking Brake (+)" side. The back up camera works great.

Sun May 26, 2024 5:57 pm

Thanks, that is good info that the "standard" parking brake circuit is something that is normally +12V when the brake is off, and drops to 0V (ground) when the brake is on.

There are some suggestions you can "cheat" this by permanently wiring to ground.
But there are other reports that newer radios are smarter and try to break this cheat by looking at patterns of voltage across several circuits.

Examples:

https://www.reddit.com/r/CarAV/comments/196175m/grounding_doesnt_work_for_my_bosss_andriod_auto/

https://www.reddit.com/r/CarAV/comments/mhafuv/parking_brake_bypass_boss_be7acp/

Mon May 27, 2024 1:00 am

As you can tell from the wiring colors, the parking brake switch simply sends a pure ground signal to the brake light housing on the dash. That's it's only purpose. On European cars, the brown wire is always a connection straight to the chassis or the negative post on the battery. On an aftermarket electrical consumer asking for a parking brake signal, just attach that wire to a ground post. If your vehicle has a newer CAN-Bus wiring system, then there might be some OHM readings encoded in the logic, but not on these relatively simple vans

Tue May 28, 2024 10:20 am

For the reverse signal, I tapped pin 7 on connector F on the back of the fuse panel. It is driven high by the PNP relay when the transmission is put into reverse.
Alternately, you can tap pin 4 of the PNP relay, which might be easier to get to.

Sun Jun 22, 2025 11:15 pm

Still trying to figure out why my back up lights are on all the time on my '02.

Trunnion, what do you mean by connector F on the fuse panel?

All I can find is that fuse #14 is for back up?

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Mon Jun 23, 2025 10:58 am

Endopotential wrote:
Trunnion, what do you mean by connector F on the fuse panel?

On the back of the fuse block (facing towards the engine) you'll see this:

https://www.xjamiex.com/mk2resource/electrical/CE2.html

Tue Jun 24, 2025 7:41 pm

I tried my damnedest to find a reverse circuit in the dash area, blue with white stripe I think. None of the wires I found has the R+ signal.

It was easier just to run a wire from the light module, under the van, up into the driver's well, into the kickpanel, across the dash internally to the DIN radio cubby. 20mins job done.

Mon Jun 30, 2025 5:35 pm

I wanted a carplay unit, single DIN, plenty to choose from. Added a backup camera at the weekend and wanted to find a reverse signal. Wire 4 of the PNP relay worked for me, and its right there below the radio. I studied the 175 relay pics to confirm pin 4, mine was black with white stripe.

Wed Jul 02, 2025 10:21 am

I have a big blob (all modesl and years) of wiring diagrams, pia to sift through.
I was looking for sw/bl tracing that around. But I must have skinned the +12V Sw/bl, because it was hot all the time. That's where I gave up.

But after searching today on the file found the J226 "PNP" relay as you noted. PNP does not come up on the diagrams

The pin #4 shows sw/gr (black/grey) then connects to sw/bl out to the lights. Dang!