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Car earths / ground query

Practical Motorsport Wiring - Club Level

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I have watched the Star grounding video a few times and I am still not 100% on whether my grounds are correct. I fully understand ECU grounding and sensor grounding as followed the Fueltech FT550 ECU documentation. My confusion is the main grounding. Just for background the engine is a SR20DET which has been installed into a Mk2 Escort and all the wiring is in design stage.

1. Starting at the battery I have a 25mm2 negative cable from the negative post to the chassis right by the battery.

2. I also have a 25mm2 going from the negative battery to a firewall connector/post.

3. From this post I have a 25mm2 going to the engine plenum (OEM location).

4. I also have a 25mm2 going from the plenum to the chassis.

5. I plan to run all my front lights, horns, fans etc. grounding to chassis ground 4 above.

6. All my rear lights, fuel pump etc. to be connected to a ground at the rear of the car.

My confusion is whether 4 above is correct - engine to chassis as I have a battery negative to the engine.

Any advise gratefully received.

I assume you have a boot, or passenger compartment, battery position rather than the OEM in the engine compartment?

It seems you're going a bit over-board, but there may be details I'm missing - that said, if rear mounted, I'd just run the ground from battery to body, and in the engine compartment from body to engine - that gives a good return for the highest drawing starter motor. Auxialries that don't specifically need a return to the ECU, or a common point, like lights, can use the chassis, voltage sensitive/sensors can use the ECU and/or a common point on the engine.

You're probably using a vibration suppressing alternator mount, so don't forget to size the alternator output AND it's ground to the engine - I've seen OEM alt' ground wires get hot enough to melt their insulation!

Hi Gord, thank you for your reply. My battery is located at the front passenger footwell. I do have a grounding wire planned from the alternator to the chassis point.

To be clear in my mind are you suggesting I do not need the cable from the battery to the engine plenum?

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