The MOSFET idea is what I'm running with trying to drive a pump from an ATTINY13a. Initial tests indicate that the MOSFET is a good fit for this type of application, however it has to be wired in an "odd" way (odd to me, anyway). Think of the MOSFET as a switch that sits closer to the ground in the circuit rather than closer to the positive terminal. Base connected to the signal generator output, drain connected to the negative side of the lights, then source connected to battery negative.
This is all from memory, so I take no responsibility for getting the wiring wrong. Good luck!
