Low Amperage Variable Voltage Input to Control High Amperage?

Hello: I am trying to add on additional lighting features into my car (350z), which has a dimming circuit controlled by the vehicle's BCM. I would love to tap directly in parallel to the wiring circuit that dims the lighting already, but I'm concerned with overloading the circuit and blowing the BCM or a fuse, as I cannot find the max load that illumination circuit would be able to handle. I would like to find a relay module that allows a low amp draw variable DCV input from ~0-15v and could control voltage output from another 12v circuit in the car (tapped directly from IGN 12v+), outputting the equivalent voltage as the input, but without the worry of amperage draw. Does anyone know of such a module?

Essentially, here is what I am trying to do:

You could use an op amp capable of high current. I'm no electrical engineer, so I don't have a circuit for you, but here's some good reading: https://electronics.stackexchange.com/questions/70884/voltage-regulator-ic-with-external-reference/70906#70906My ex once told me I have a perfect face for radio.

A P-Channel MOSFET is all you would need (along with 2 resistors). The appropriate device would depend on how much current you want to draw.

Thanks guys. I like the OPA549T for the purpose. Looks like I can configure it to accomplish what I'm looking for.

The OPAMP is a poor choice for your application for many reasons. It can't accept input voltage greater than V+ minus 2.3V. It can't output more than V+ minus 2.7V A good heatsink is required. An FQP27P06 MOSFET with a 20K resistor between the Gate and +12V and a 1K resistor between the Gate and your control signal would work.