head unit - power supply wiring question



I'm about to replace my stock head unit with a Pioneer unit.

The car (Merc) has an ISO connector and according to everywhere I've asked/checked I should not need any adapter to connect to the Pioneer head unit.

The problem is that I'm not getting any power to the head unit. I've checked with my multimeter that there is power running right through the wiring and plugs.

I notice though that there is a connection/wire on the Pioneer for positive power from the ignition. I've checked some wiring diagrams online for ISO connectors and this seems to be missing from the ISO connector on the car side.

I have constant (negative) 12v at pin 4 and negative(earth) at pin 8.
What I don't have is ignition 12v at pin 7 and I don't see one anywhere in the wiring loom connected to the (car side) ISO connector.

I notice that a hands free kit that was installed has basically used the constant (negative) 12v to supply both negative 12v feeds to the car kit.

Is there any reason why I should not do the same thing with the head unit - that is : supply the pin 7 ignition connect with 12v from the pin 4 constant 12v ?


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For the benefit of anyone searching with a similar question in the future :

basically for some reason the Mercedes ISO connector didn't have the 'ignition' or 'acc' positive wire - possibly because the stock stereo system that comes with the car was integrated with the dashboard system.

Anyway. I figured out how to lift the fascia around the gear stick, removed the ashtray & cigarette lighter etc. Got an ignition/acc positive connection from the cigarette lighter and wired that into the system. Problem solved.

Definitely need to have a multimeter or other voltage tester so that you can be sure you know what you're tapping into.
Hi guys,

For reference using a constant power supply for acc/ign and batt is not a big problem! The only issue you'll get is that the stereo won't turn on and off with the ignition! You'd have to do that manually! BUT if you only had an accesorie live and no constant then this can be VERY annoying as every time you switch your ignition on and off the stereo will reset, spit out the cd and ALL your radio stations will be lost off the memory!

Hope this helps someone! :hiya:

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