there is an alternative option of wiring a JFET so that it takes a feed off Fan A and the 12 V Molex to control Fan B all from the same 3pin fan connector.
Too much bother tbh, I'd have to go out and buy a JFET so I may as well just go and buy some fans that actually work with 3 pin connections XD.
a JFET is like $.50 to $2 depending on where and how robust you feel you need to get.
The point im trying to make is that if I was going to buy a JFET then I might as well buy fans that actually work with the mobo. I'm not trying to wire the fans to save money, it's just that I can't be bothered going to buy some more fans.
From what you posted now I think that as @Dexter_Kane said that the +5V are used to generate +7V. That means, that the fans internally are connected between +5V and +12V which in return results in +7V on the fans motors as +12V - (+5V) = +7V
. If they run to loud like that you can try and hook the +12V rail to +5V and the +5V rail to ground as well, this way there should be +5V on the motors of the fans... but its likely they wont spin at all.
Do they spin if you wire it like that:
12V fan A to +5V molex
12V fan B to +5V molex
5V both fans to GND molex
GND both fans to GND molex
I can test this wiring in about an hour, will get back to you once I can.
No luck with the wiring you suggested, I guess I give up then.
Than these fans need the 12 and 5 V to do what ever they internaly do with it.
I think you're going to be better off just replacing the fans with something less weird.
MAC fans are not the same as stranded PC fans as they get there logic voltage 5 volts in this case from the system board.
Just connect 5 volts to 5 volts. And ground to ground. And then very the 12 volt voltage to change the speed of the fan.
I should also mention that these fan pull a lot of amps so its not a good idea to connect 12 volts to a fan header.