Battery isolator advice?

Hi,

I’m new to wiring and struggling to understand the wiring diagram in regards to the the engine isolator ‘suggested cut wiring’ as in the attached wiring diagram.

The bit I’m confused on is where in the ignition circuit does this cut off relay fit in.

1. terminal 87 from ignition circuit? Where from?

2. To engine IG power? Where to?

I want to wire it up with one main relay that once is live, kicks in the fuel, ignition etc. but were does this ‘engine cut off relay fit in to the circuit?

Any help would be much appreciated? It’s to fit in a rally car.

regards

justin

Do you have an ignition switch? The +12V output from that switch would have the relay inserted between that and the things it powers (like Ignition coils, maybe ECU, etc) If you have a key switch (like a road car), then you would find the output from that key switch that turns on (12V power) when in the run and start positions (ie, Ignition Power), and insert the relay into that output from the switch -- be careful not to get the accessory output -- it will be on in the RUN position, but not in the Start position typically.

If you are wiring an igition relay, this could either be on the positive trigger side of that relay, or on the relay output. Either should work.

Before getting into it too deeply, I'd suggest a careful read of the RAC "Blue Book"- if they still do that - to see exactly how the cut has to be fitted, and what it needs to control, maybe talk to a head scruitineer/certifier.

Thanks all. Here’s a few more details…The car is a rally car and the battery cutoff needs to isolate all battery circuits and completely stop the engine.

The car has already got a professionally built engine loom. I’m just wiring the dash, lights, interior and exterior wiring.

So, back to the engine cutoff and relay terminals 87 and 30 which I’m unsure how or where to wire up? (See attached wiring cut off diagram)

As the engine loom is already complete and ignition circuit finished. I can see that the Ecu (DTA s80) needs +12v power and also +12v switch ignition power. Can I wire relay terminal 87 to the +12v power or +12v switch on the ECU and would it be safe for the ECU? If not how do I make it safe? And power coming straight from the ignition switch to terminal 30? Or just bypass the Ecu and modify the ignition circuit somewhere else to stop the engine?

I hope that makes sense?

Quite often you will need a multi stage attack with a kill switch, as you have to be able to stop the engine so that the alternator is not energising the power circuits. I have seen a number of vehicles keep running when doing checks of kill switches as they have cut the battery, but the alternator keeps the engine going. You need to cut the power to the coils and or injectors when the switch is thrown to ensure that the engine stops.

The other thing to be aware of is that if the battery is disconnected before the engine stops, the current being generated by the alternator that is normally going into the battery has to go somewhere, this is why the four pole "Big Red Switch" kill switches came with the ballast resistor, so that the alternator could load dump through there, rather than finding the path of least resistance (which on a race series that I worked on, was the ECU) back to ground.

Ok, I’ve drawn up a basic ignition wiring diagram to incorporate the battery isolator. (Brise/tyco ev200)

Can you tell me if it will work? Any advice would be much appreciated.

1st attachment is the isolator diagram.

2nd attachment is my wiring diagram

Thanks.