Are you leaving the key in the ignition with it in "ACC" position for long periods of time? If not, then having an accessory switched circuit or a Ignition controlled circuit doesn't make lick of difference...other than the relay cycling twice during starting of the engine. Just change your setup to use the Power point fuse in the panel instead of the EFI. Playing with the EFI controller's power is a bad idea. Maybe I'm just dense (ask my wife, she'll let you know), but what's your need of a circuit that only powers when the engine is running? You're not going to draw enough out of the sienna battery during the moment you pass through the ACC point in turning the key to drain it to the point where it won't start.brian_bp said:A simpler low-voltage cutoff device in the control wire for my basic trailer power relay would suit me better, and make me more likely to use an accessory circuit (instead of ignition-switched circuit) for control.
I've got a relay setup similar to yours, but on a switched circuit in the network of wires under the glove compartment inside the vehicle. My "off" switch and relay are inside the engine bay by the windshield washer fluid tank. I also run a second fused wire to the rear and have a circuit that isolates the running lights/brake lights/signal lights. These get switched through a number of P-channel Mosfets to control the light action of the trailer. Completely isolates the sienna's lights from the trailers and has no moving parts. Works like a charm and can push 20 amps through each circuit, if required.