Proper Grounding PDM harness?

Hi guys,

Still researching on my own, but basically here is where I am:

I built the full chassis harness for power (12V) circuits only. Now I need to design the grounds. So from what I have researched the best method would be to run all the grounds to the engine, but that seems impractical. What I am thinking is single main ground from the battery to the engine, and then a large ground to the chassis from the engine? Ground all relative circuits (headlights, radiator fans etc to the chassis via short grounding wires.

Not claiming to be a genius on this obviously. All help appreciated.

I find it to be convenient to have a good chassis ground near the PDM that things controlled by the PDM are grounded to. So you basically have two wire power leads to each device.

Random question, if I have a PDM powering everything and is also the ground point for everything, and it's connected directly to the battery positive and negative terminals, is there a need to add ground wires to the engine and chassis?

I'm asking because I see that star grounding is the golden rule, but do I need to in this case? It's a motorcycle so it's all short runs.

Also, is there advantage in having the coil grounds grounded separately to the engine like I've been reading?

Generally, your starter (one of the highest current devices on your bike) will be using the chassis ground - so a good ground strap from the engine/transmission/starter to the chassis / battery is important. Smart coils often have a specific ground that is to be connected to the cylinder head.

Forgot about that one connected to the starter.

So I should connect that to the frame, then add one from there to the battery and then one from the battery to the PDM?

The PDM normally doesn't need much ground current. It is only switching the high-side (12V) to devices on the vehicle. I would consider the battery connection to the chassis to be the main ground from a star point, so that is where I would connect the PDM's ground and any other devices that are voltage critical (like ECU, fuel pumps). Lights & fans can just use a local chassis ground.