I have a device called a battery brain. It disconnects the battery when it sits at 11.8v or lower for a few seconds. It test out fine on my "bench", an old optima that holds 12.2v and an old Southern VP red/blue light bar. I watched the voltage, it had 12.1v before hooking anything up. I put the BB on the stud, then moved my DMM leads to switched side of the BB and the ground post, still 12.1v. I then hooked the light bar up just like the DMM. It ran for about 5 seconds and the BB clicked, shutting off the bar and the DMM read 0v. I put it on my truck again. The power dist is set up as so (using tsunami parts.) The alternator has it's own 1/0 wire going to a 250amp fuse (230 amp alt), 1/0 between the fuse holder and the + battery terminal. The Accys run from the battery terminal to a 200 amp fuse then to the battery brain all with 4ga wire to a distribution box with 60a fuses. It does not work right, it clicks but it doesn't disconnect the power. It has a solid ground, and I tried leaving it hanging so my mount isn't the trouble. Anyone have any clues about these things and if they dislike fuses?

 

Are you reading the voltage after the device with just the meter? Or are you trying to start the truck? With just the meter you may get a voltage after the device that doesn't mean anything, but the truck may still be disconnected(won't start).

 

Yes I am metering voltage after the BB. I tried it with the head lights on to bring the battery down to 11.8v. The headlights did not turn off like they should have when the brain clicked.