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RButcher, BMW Technician
Category: BMW
Satisfied Customers: 103
Experience:  BMW Factory Master Mechanic, 609 A/C Certification
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Connect a positive cable to the ignition switch of a BMW Z3 1.

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How to connect a positive cable to the ignition switch of a BMW Z3 1.9 1997 Roadster

what are you trying to hook up?

Your best bet would be to go to the fuse box and find an open fuse slot that has ignition switch terminal and use that as your hook up point with out your device possible back feeding into a module and costing you some money.

Customer: replied 9 years ago.
I have to connect to the ignition switch a supplemental hydrogen cell generator, so that when I turn the switch on, the relay of this device connects the 12 DC current and starts working. It should work only when the car is running. When the swicht is turned off the device should also stop working, so that the hydrogen is not accumulated.
The only instructions from the manufacturer of the device, are to connect the positive cable to the car ignition or to any ACC cable. I want to do this without damaging my car and in a way that it would operate safely. I don't like the idea of connecting this to a fuse slot.
The modules in BMW cars are very sensitive to outside voltage inputs and going directly to the ignition switch can cause a back feed that could take out the engine computer and or the anti-theft. By going to the fuse panel this will protect the rest of the computer in your car as it was designed to do by the factory. Remember you should use an open fuse opening which will be identified by only one terminal in the fuse slot. Just put terminal on a wire and put it into the fuse slot on the open slot and put in the recommended fuse size for your kit. Also remember running straight to the ignition switch you increase your amperage load on this circuit and cause the switch to wear out sooner or blow other fuses in the car that use that same wire. So seperating your kit in the fuse panel will be safer and look more professional.
Customer: replied 9 years ago.
Thank for your answer. The only problem I may have later when I do this connection is how to identify the right fuse slot that is connected to the car switch. I am not a Technician, so can you be more specific and detail to me the way to identify the proper fuse slot. This kit comes with a relay and a green 30 AMP fuse connected to the relay and will also be connected to ground.
A test light will work but you are much better off going and getting a digital volt ohm meter at the local auto parts store or hardware store, shouldn't be more that 20 dollars for a basic unit and it will help you down the line if there are problems with anything. Take the black negative lead and connect it to a metal part on the engine or the neg. post on the battery. Take the red positive lead and put it in the fuse slot onto the single terminal and observe the voltage level. If you have 12 volts with the key off this is called HOT AT ALL TIMES power, you are looking for the voltage reading to be zero with the key off, now turn the key to the run position ( the position the key is in after letting go of the start position) and see if you have your 12v now. This would be call KEY ON or ignition switched depending how your kits instructions word it.
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