I am building a new system using an older Ultra computer case.
The Ultra case has an 80mm fan in the front to blow air into the case. It also has a 120mm fan in the back to expel air from the case.
The GIGABYTE GA-MA785GM-US2H motherboard only has three fan connectors.
I have the processor cooler plugged into the CPU_fan.
The 80mm Vantec fan in the front of the case only has 1 3-pin plug with black-red-yellow wires. I have this plugged into the Sys-fan plug.
The 120mm Vantec fan (TF12025) has 1 yellow wire attached to a 3 pin plug. It is only connected to 1 pin of this plug.
The van also has two Molex connectors - 1 male and 1 female. It also contains an adapter - 1 male and 1 female Molex to a 3 pin plug. The plug only has 2 pins in it.
How should I connect this 120mm fan to the motherboard?
I'm not using the NB_fan (the Northbridge fan) connector.
Would I connect the fan Molex connections to the adapter and plug it into the NB_Fan?
My guess is your Vantec fan is an interesting intermediate design. It is set up with wiring to supply power from a PSU Molex 4-pin output connector, and then the second connector just replicates the one already "used" so you don't lose a Molex. This part is relatively common. What is interesting is that it also has a separate connector to go to a mobo fan pinout that has only a yellow wire to it. That wire is the fan's speed signal. So this fan can feed its speed into a mobo connector in case you want to know what it is. BUT with power supplied only from the Molex connector (which is always the full 12 VDC) the fan will always run at full speed. So although your mobo could tell you the fan's speed, it cannot control it.
If you have another fan and want to run it from the second mobo SYS_FAN pinout, just do NOT connect the single yellow wire from your Vantec to anything. You won't know the fan's speed, but it can only run full speed anyway.