First, are you sure that tap is hot? Maybe it's a box that is used on other models, but maybe there is no bus behinf the open tap when it's used in a Mx3.
Also, how is it rated at 7.5 A? Is there a fuse in it? If there's no connected load, why is there a fuse?
Connecting 2 X 15A is a pretty big increase in possible current. I'd look at whatever the bus supply is before I'd add that much.
I don't understand. If there is no fuse in it. how is it powering METER2? How are you using 2 fuses? Are you using some kind of double tap?
When you ask a question like "What do you mean hot?" it makes me think you should find someone who understands electrical systems and who has actually looked at the car. There's lots of bad advice on the innernets.
I "think" the add-a-fuse type devices that I have seen work like this:
1. A fuse in a port in the vehicle's fuse box is removed and the add-a-fuse device is plugged into that original fuse box port.
2. The add-a-fuse device has two ports for two fuses: the first fuse port is where the original fuse removed from the fuse box is placed, which protects the original appliance that the fuse box was protecting. The second fuse port is for a newly added appliance and is there to protect it by an appropriately sized fuse.
Now, the OP asked why is the fuse port that was empty is specified at 7.5A. My assumption is that some vehicles using the same fuse box have an appliance that is protected by a 7.5A fuse placed in that fuse port. Since there is no fuse in that fuse port, obviously the OP's vehicle does not have that appliance, so the factory does not supply a fuse for that port.
So, the OP might not have to put a fuse in the add-a-fuse's first fuse port because it would just be energizing a circuit for a nonexistent appliance. The second port with an appropriately sized fuse can be put in the second fuse port to power the new appliance, e.g. fog lights.
I've described more than I know, so I can't testify to its veracity. My head hurts.
Fog lamp DRL. i am tapping in the engine compartment fuse block. Isn't the cig fuse in the inside?
I am indeed using a 5A fuse for the DRL fog light covers. I'm not sure of the Amperage rated for it, as that mine are Chinese haha. I do know that they have very little electrical draw though.I will do that once I get my 10A and 7.5A fuses. Are you using 5A there? Isn't the fog DRL drawing 6A? Or maybe you have different one.