Master Power Cutoff

[Ponymedic]

Need Ideas from the group.
Purchased and planning to install master power cutoff switch with removable key as well as jumper terminals. My thought was the jumper terminals in the trunk but unsure about the master cutoff.I know many install between the seats on the rear wall trans piece but unsure if there are better Ideas. finally interrupt positive or negative? I want to say positive but that would allow the engine to continue to run once started..

Thoughts from the group?
Carburetor 302
drop trunk and battery

[BEAR-AvHistory]

FWIW. Might be a better place but have not had any issues with the switch on the u-joint cover.

EDIT: Should have put thins in Have a 10amp self resetting circuit breaker on the switch. Keeps the ECU & radio memory alive with the key out but the car will not start.

[Jacob McCrea]

I have mine to the left of the steering wheel on the dash (Type 65), positive side, so I (and someone outside the car in a crash) can reach it in a big hurry. You can wire it as a true kill switch on the positive side, and I did that, carefully following instructions I found online. If I did it right (we shall see) it will shut down all power, and interrupt the alternator output, thus killing the engine, without frying the alternator. Electricity is not my strength and it took a lot of reading to figure out how to do that, and I'm still not 100% sure the alternator won't fry when I turn the switch.

[Avalanche325]

My thoughts.

There is a difference between a master cutoff and a battery cutoff. Most of us have a battery cutoff. A master cutoff would have two sets of contacts. One for the battery and one to interrupt the alternator.

Between the seats is a good place in my opinion. Easy to insert and remove the key. Unless you put your harness on with the key still in your pocket. It is almost invisible when the key is out, so a thief won't know it's there. On a race track it would be visible to a tack worker if really needed.

Put it on the positive. Putting on the negative wont turn the car off either. The battery is not the power supply for the car, nor is it the ground. The alternator is the power source and it is grounded to the engine and chassis. Cars run fine without a battery. They're just a little hard to start.

I ran a wire, fused of course, from the battery positive to my clock.

[CraigS]

I don't have one since I moved that battery up front. When the battery was in the back the red flag switch was in the trunk too. The few times I went into a restaurant where I couldn't watch the car, I pulled the flag and locked the trunk. BTW it's been 6 years and I haven't missed the switch even once.

[Avalanche325]

BTW it's been 6 years and I haven't missed the switch even once.

They are worth at least 10hp, so I'm keeping mine.

[silver_pilate]

I ran the same setup you are considering. My battery is grounded to the frame in the back with a lead running to a jumper terminal in the trunk, and the positive cable runs to a jumper terminal in the trunk and then up to a battery cutoff switch mounted at the rear of the transmission tunnel cover (on the angled piece). I did what some other members have done and mounted a 10-amp auto-resetting circuit breaker (blade style) in a fuse holder. It serves to "jump" the battery cutoff and provide 10 amps max current to keep the memories alive on the clock, etc when the battery cut-off is turned off. I've read that these can fail on occasion due to increasing levels of load trying to get through them as they weather, or if you forget to turn the cut-off back on and attempt to start the car. Then again, I've also read that they work well for years and years. I guess I'll see what happens with mine. I'm hopeful to do first start this weekend.

I view a battery cutoff as an extra safety not only against theft, but also as a protection against all of that potential energy housed inside the battery. My alternator has a mega fuse in-line to protect against that side of things.

[Ponymedic]

Could always use an extra 10hp

[GTBradley]

They are worth at least 10hp, so I'm keeping mine.
I got 11 out of mine.

[BadAsp427]

I installed my battery cut out switch up in the passenger foot box top inside front corner. Totally out of sight and in fact actually left the carpet a little loose there so it is actually behind the carpet. I used it every day during the Hot Rod Power Tour when I went in for the night. Only negative issue is that the power connections are on the inside of the engine bay and while working on the headers one should disconnect the power at the battery as it is easy to ground out. But on a positive note, that also provides a great place to "jump" the battery if needed. It also provided a great place to put the wires + wires -vs- all on the starter. Worked out real well for me. I'm mentally designing a nice cover to go over the wires to clean it up a bit. And FWIW, my son who road shotgun for the past week and logged 2500 miles with me, was able to reach down and switch it for me pretty easily when needed.

109248

[John4337]

I put my battery cut off on the horseshoe above the transmission tunnel. With the key out, you don’t know it’s there. I see it as a theft deterrent on trips. With it out, everything except the clock and EFI memory is dead.

Sadly, I can’t verify Avalache’s claim of extra horsepower....

John

[Big Blocker]

Mine is mounted on the upright between the trans cover and underside of dash . . . been there 17 years with no issues (that should answer the question about longevity). Mine is wired to cut off the alternator "exciter" lead (thru a relay) so the alt stops producing voltage and the engine quits along with everything else. That only works if you have an earlier alternator with a "stator" terminal - Old school racers trick for extra HP (above the 10 mentioned above).

Doc