Installing Battery Switch, want to cut ALL power

wiredwrx · May 24, 2007

Hey All,

I got a battery switch, rated at 110 or 120 amps. I want to use it in the race car, as the main power switch, so that the car will turn off when I turn off the switch. Of course, I have the switch between the battery terminal and the cars wiring, but since the Alternator is supplying power to the car, removing the battery fromt the system doesn't shut down the car. I want to connect the alternator to the battery BEFORE the switch, so that ALL electrical power flows through the switch. I have looked at the alternator, and it looks lke there are a couple of wires leaving the alternator. Can any one help me identify the wire I should "interupt" Can this be done. I have looked at the service manual, but the description of the alternator and charging system is sorely lacking.

Thanks for the help,
Michael

Skywise · May 24, 2007

why not switch the battery's ground

quazz209 · May 24, 2007

Skywise said:
why not switch the battery's ground

I would agree with this, it is the simplest way for the switch to function. However I might check the rules of the sanctioning body that you are building the car for. Some of them require that the postivive needs to be interrupted; not the ground if my memory serves me correct.

Sean485 · May 24, 2007

First of all Skywise please work on your grammer as per rule 7...

Secondly installing the switch on the ground of the battery will do nothing that having it on the poisitive side wouldn't do. The alternator makes electricity so as long as the alternator is still charging the battery is just there as a reserve/buffer for sudden voltage spikes/current draws.

To the OP if you search this has been discussed many times and you have the correct idea on how to wire it; the wire you want is the one with the 10mm nut on it (terminal "B"), the other 2 are for the alternator relay and the idiot light in the dash. Run a proper gauge wire (I run 2ga from the battery to the starter/accessories and 4ga for the charge-back wire) from that terminal ("B") to the same terminal as your battery hooks to on your cut-off switch.

Skywise · May 24, 2007

If you would be so kind as to point out my grammatical errors, I would be so grateful because I have no idea what you're going on about. Secondly, the reason I suggested the ground is because its simpler where you only have 1 common point to interupt, and the negative terminal doesn't have the fuse block to work around. But you're right in that since its a circuit you can break it anywhere you find convient. As a casual aside dsms are electrically engineered as a ground switched system. (some headlight harness manufacturers don't support some imports because of that, domestic cars are positive switched)

wiredwrx · May 24, 2007

Thanks for everyones response. I will do some more research as well, though all are viable choices.

Michael

Sean485 · May 24, 2007

Skywise said:
If you would be so kind as to point out my grammatical errors, I would be so grateful because I have no idea what you're going on about.

Lack of ending punctuation and lack of capitol letter at the start of a sentence?

joebag · May 25, 2007

quazz209 said:
I would agree with this, it is the simplest way for the switch to function. However I might check the rules of the sanctioning body that you are building the car for. Some of them require that the postivive needs to be interrupted; not the ground if my memory serves me correct.

The reason to cut the positive is that the positve connection could find its way to ground. A short any where in the electrical system woould complete the circuit. It would be best to stop the power at the closest point , which would be the positve post. Think of it this way. the power comes out of the positve post and runs thru the wires all over the car and return to find ground. If it finds the ground in a bad alternator or a bad wire rubbing at the block or frame it will complete the circuit. This can't happen if no juice at the battery. Hope this was helpful.

Joe

4SFED4 · May 25, 2007

I recently changed my kill switch to cut the ground.
By killing the ground the switch lasts longer and it reduces corrosion build up on your terminals.

Also if you have a modified stereo system in the car and you kill the power through the positive you can get nasty feedback through the speakers connected to the amplifier(s).

As far as the NHRA rules go, it doesn't specify how to hook it up other than you need visible, written "OFF" direction and that it kills the engine.

When I hit mine everything is dead in the water, works great.

If you go the positive route and don't rewire the alternator, it can keep the car running, it did on mine. That can be solved by running an 8 gauge wire from the B terminal of the alternator directly to the positive terminal on the battery.

dsmskyline · May 25, 2007

Even if you kill the ground with the switch the car will stay running as long as your alternator is working properly.

The switch is meant to kill the power to everything, the motor shouldnt stay running when the switch is turned off.

Thomas
90 TSi AWD

4SFED4 · May 25, 2007

My car won't, the TEC3r loses ground it dies, same with the Aeromotive fuel pump.

Installing Battery Switch, want to cut ALL power

wiredwrx

Skywise

quazz209

Sean485

Skywise

wiredwrx

Sean485

joebag

4SFED4

dsmskyline

4SFED4

Top Contributors this Month

Recommended Communities