Reverse control signal access points help request

[Gebbly]

I'm planning an android head unit in my Z4M and working out all the wiring in my head. I'm now trying to figure the reverse camera that I plan on using. The head unit provides a specific rear camera power wire which is good. So the reverse camera can send signal directly to the head unit and get power directly from the head unit.

The head unit also has an input wire for a signal telling it when reverse has been engaged. This powers up the camera and switches the head unit to the reverse camera view. I am now trying to figure out how to get this signal to the head unit. I can think of 2 possiblities but I'm hoping the collective wisdom here has a few more ideas.

1. I have seen a SimpleCarGuy youtube video in which the camera power is wired directly to the car battery (via a relay triggered by the reverse light) and the camera uses its normally power wire to send the reverse signal back to the head unit. This works but I would prefer the camera to get power direct from the head unit and for the head unit to get the reverse signal direct from the car rather than routing through the camera cable.

2. Another option is for the camera to be only connected to the head unit for power and video signal. And then I think the Z4M has a "gong unit" as described here. The gong unit lives near the driver. From the diagram I think I can wire in to the T5 "Japanese Reverse Warning" which is sending 12v to the gong unit when in reverse. I can then connect this directly to the head units reverse control wire. This feels better than option 1 as whatever is informing the gong is also informing the head unit.

3. Apparently older cars had a wire coming direct from the gearbox that went live when reverse is engaged which could be wired in to the head unit reverse control wire, I dont know if this is the case with the Z4M. Anyone know?

Can anyone think of any other way I could get a signal from the front of the car to the head unit when reverse is engaged?

 

[Gebbly]

In case anyone searches for this in future I'll update it with what I find. Another option that occured to me would be to use a fuse tap and tap straight into the reverse light fuse in the fuse box.

 

[Usel]

I'd say the reverse switch is likely on the side of the gearbox and then goes underneath the car to the boot. I doubt you can pick up a wire inside the cabin to tap into so the reverse tail light will likely be the easier option.

 

[Gebbly]

Thanks for the reply Usel. Thats a bit of a nuisance. I guess I may have to run a cable all the way from reverse light back to head unit then.

I had a look at the fusebox behind the glove box and am trying to decipher the symbols on the card showing which fuse is which.

Nothing looks obviously like a reverse fuse

 

[Usel]

On facelift Zeds it looks like from the gearbox switch it runs to the fuse box under the bonnet near the strut tower and then back again through the cabin under the dash and then somehow to the rear of the car.

The nest of wires under the dash isn't really something you want to start going through but the wire colour is blue and yellow which isn't that commonly used so you may be able to spot it.

 

[Usel]

Ok from this photo there is a blue and yellow wire which may or may not be the wire you need but its running to the boot with the positive lead to the battery.



If you remove the drivers seat and trim around the door you will be able to lift the carpet up find these wires.

Run a cable from the rear light wire and have one prong on the multimeter on that wire and stab the other prong into blue and yellow wire under the seat carpet and see if you get a continuity reading.

 

[Gebbly]

Crikey Usel thats an amazing level of detail, thanks so much. Looks like those are my 3 options then. If I get things working I will be sure to report back