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Relocated Battery Ground & Power Layout

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi Guys,

I'm looking for some feedback regarding trunk mounted battery wiring layout I'm working on. I wanted to design a layout so that it can easily adapt to future modifications if needed and avoid multiple grounding points. See attached diagram.

For Ground wire: Battery => Isolator => Firewall bulkhead stud => Engine

-My thought process here is that I would use the firewall bulkhead stud as my power grounding point at the front of car for anything that needs a power ground and if needed use the battery isolator stud as a rear grounding point with everything leading back to the battery.

For Positive Power wire: Battery => Circuit breaker => Firewall bulkhead stud => Alternator, Starter, ECU/PDM, OEM Fuse Box.

-Just like the negative wire my thinking here is that I would use the firewall bulkhead stud as my positive point at the front of car for anything that needs power and if needed use the circuit breaker as a rear power point.

I appreciate any feedback/recommendations you guys have. Thanks, Marko.

Attached Files

Is this for a road car, or a race car? A lot of ASN's require that the Positive circuit is broken by the battery isolator, and will not accept having the negative being used only.

At the moment it's just a street car, but I'm building towards time attack/road racing.

BlackRex is correct. Even for a street car, if you are going through the effort to redo it all, you should do it correctly.

Check out the DataPanel 30021 for a solid state isolator. Pretty inexpensive and work well.

Any particular reason your running the ground all the way to the block instead of just grounding to the chassis?

I appreciate the feedback. I planned on running the Cartek isolator which uses the ground wire to isolate the battery and it seemed like an easier setup since I don't have to worry about the alternator continuing to provide power. Plus my current ECU doesn't have the input to receive a "shut down" signal that some isolators support like the MSEL.

For grounding I wanted to have one star grounding point. I could potentially have two, with one being at the front thru a chassis ground and one at the chassis rear for the battery.

Disconnecting the Ground from the Battery will not stop the engine if the alternator is still powering the vehicle. The vehicle grounds for the engine and other components such as the ECU will still be in place to keep the engine running.

The reason for having the battery isolation switch in a race vehicle is not to stop the engine, but to isolate the battery supply voltage so that the vehicle doesn't become live from the battery cables being damaged in a incident. The engine is usually killed by a separate (lower current) circuit in the master switch that powers a primary device (Ignition coils/ECU/Injectors/Fuel pump circuit) that is also broken when the switch is moved to the isolated position. The approved motorsport isolation switches also have another circuit in the switch that is made when the switch is moved to the isolated position and is designed to be connected to the alternator supply on one side, and to a load resistor on the other, this load resistor is designed to be a high enough load that it will drain all of the current out of the charging circuit in a safe manner.

Example setup

Great info, thank you. With that in mind I think it makes sense to plan and route the wiring so that an isolator can be added at a future date once I get the proper ECU/PDM and utilize the low current signal from the isolator.

Aside from the isolator what are your thoughts on the star grounding with the battery in the trunk.

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