Isolating battery

Looking for information on mounting a relay at the stock battery location behind the rear bulkhead on my L21B, with a switch on the inst panel that will kill the power to the Master switch mounted on the right wing root panel.What kind of approval is required.?

A log entry from a A&P.

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you will still have a small hot wire coming from master solenoid..... for master switch... that will get grounded to turn it on...

best to relocate all electrical out of wing root....

What you are doing is making the electrical system turn on and off just like every other aircraft (except small Pipers). Not doing anything radical. Look at the master relay wiring for PA-28's or even Cessnas, for examples of how it's done.

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Just trying to remove the potential ignition source in case of an accident.I would probably use only in an emergency or a difficult landing situations,which many of mine seem to be now days.Thanks much.

IF, and I mean IF, your wires are in good shape, (seriously here!), you can simplify your electrical system with mostly existing wires and get what you are trying to do fairly easy.

Install a master relay on the side of the battery box, and connect it to the start relay with a bus bar or a short cable. Next, take ONE of the wires that run from the dual fuse block to the original master switch and connect it to the battery relay along with the bus bar to the start relay. Now go to the back of the master switch and connect the wire that now runs from the master relay, to the short bus feed wire and insulate well. Remove all unused wires at this point. Go back to the master relay. Assuming you are using a relay with two small terminals, install a jumper wire from the hot terminal for the battery positive, to one small terminal (doesn't matter which one). Then connect a 20 gauge wire to the other small terminal and route it to the master switch. Remember disconnecting those big feed wires? Connect that 20 gauge wire to the center terminal. Connect both of the other terminals (should be a top and a bottom one) to ground. Finally, connect the battery positive to the master relay

Now you have a 'real' electrical system. Pushing the master switch toggle up or down will turn on the master relay, providing power to the start relay and to the bus. If you have an electrical emergency or a stuck start relay, just flip the master switch to the off position and all electrical power will be shut off at the battery box. Safer for you and safer for your wiring.

The best fix is to move the bus to the instrument panel, including a new master switch. That gives you the above benefits and also moves the bus and breakers away from the fuel tank area.

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