MSefi.com read only forum (Jan.15,2018)

Hi all,

I am planning to relocate the battery back in the trunk. I'm using a relay board with negative connected to the engine. The engine is connected to the chassis down the firewall by a cable. I know negative can give issues. Can I connect the battery negative somewhere in the trunk or should I run a cable to the front and connect it where the engine is connected down the firewall? Or should I connect it to the engine?

Thanks in advance!

GGR wrote:Hi all,

I am planning to relocate the battery back in the trunk. I'm using a relay board with negative connected to the engine. The engine is connected to the chassis down the firewall by a cable. I know negative can give issues. Can I connect the battery negative somewhere in the trunk or should I run a cable to the front and connect it where the engine is connected down the firewall? Or should I connect it to the engine?

Thanks in advance!

Assuming a steel body normal unitary construction, it's usual to ground the battery locally.

Thanks.

Yes, it's a steel unitary body. I'm asking because I remember reading in the manual that the relay board negative should be connected to the engine and as close as possible to the battery negative terminal. I assume this requires having the battery grounded not too far from the cable grounding the engine to the body.

I also read this on a Mustang forum about relocating the battery in the trunk: '"The disavantages [of relocating the battery in the trunk] are with computer controlled cars, the ground side is further away, and the steel isn't the best conductor compared to copper or gold and this can fool with sensors. Many people run a negative cables from where the original negative cable hooks, to the back, and some also like to put the computer grounds on their own circuit to the battery".

GGR wrote:Thanks.

Yes, it's a steel unitary body. I'm asking because I remember reading in the manual that the relay board negative should be connected to the engine and as close as possible to the battery negative terminal. I assume this requires having the battery grounded not too far from the cable grounding the engine to the body.

I also read this on a Mustang forum about relocating the battery in the trunk: '"The disavantages [of relocating the battery in the trunk] are with computer controlled cars, the ground side is further away, and the steel isn't the best conductor compared to copper or gold and this can fool with sensors. Many people run a negative cables from where the original negative cable hooks, to the back, and some also like to put the computer grounds on their own circuit to the battery".

Well, my BMW has the battery in the boot and grounded locally. And more electronics than you can shake a stick at.
The important thing is to ground all the sensors for each individual processor at the same point to prevent differential currents flowing. If two processors have to communicate and you can't do this to both, use some form of balanced line etc that doesn't have a ground reference.

All IMHO.