2 power supplies to single device

[Hillbilly123]

I have car reversing camera with a permanent power supply with a switch to turn it on & off. I want to also have a supply from the reversing lights to turn it on when parking and the permanent supply is turned off. I presume a relay will work but am unsure how to wire it up. Reason is that the permanent is for when caravan is attached and second camera is working all the time when travelling. I realise I could just flick the switch but it can be busy when parking and would be good if this can be done. Hopefully someone can advise me.
Main problem is what happens if I hook both up together and rev supply comes in when perm is still on
Thanks
Graham

Can I just connect the second wire from the reverse lights to the positve between the switch and the monitor and put a diode in each line to stop backfeeding to each other. Some advice would be good thanks

 

[Analog]

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Can I just connect the second wire from the reverse lights to the positve between the switch and the monitor and put a diode in each line to stop backfeeding to each other. Some advice would be good thanks

That would be a good idea.

 

[Hillbilly123]

above

Thank You any further explicit help would be appreciated as I dont want to fry a $50,000 4x4 by doing the wrong thing

 

[JimB]

$50,000, must be one of those cheap ones!

OK have a look at the attachment, that should confirm what you are already thinking.

It also occurs to me after I have drawn it, that it does not matter which is wired first the diode then the switch as shown, or the switch then the diode.

JimB

 

[Hillbilly123]

Thank you Thats what I was thinking Actually it was $50k second hand here in Australia but as its the only one I have i'd like to keep it. At least its not a Land Rover.

 

[JimB]

I thought you were in the US with the reference to $ and a nom-de-plume like hillbilly!

OK what sort of 4x4 is it? You obviously have a bit of a downer on Land Rovers.

 

[Hillbilly123]

Not really, just they dont seem to stand up to the sand and the outback conditions. In a recent test on 6 different 4x4s the latest Rover was no 6 and came home on a wrecker as the electronics couldnt hack it. Mine is a Nissan Patrol actually which is no 2 to the Landcruiser. The nom de plume is a dig at my real surname and yes we do have $ here.
We did have a Landrover in the 60s which we couldnt kill. Even after we sunk it we got it to go again.
Sadly since then they have gone down hill (pun).
Will hook up the wiring as drawn with diode and second supply after the switch so that it will activate camera regardless of the switch position.
Thanks
Graham

 

[JimB]

Yes the British motor industry has been through a bit of a bad patch (the last 40 years?).

I am aware that you have $ in Australia, even if they are made of plastic!
A very practical idea, saves destroying them if they are left in your pocket when the trwsers go in the washing machine.

I visited Perth a few years ago, a three week combined business trip and holiday. A very pleasant experience.

JimB