Gauge grounding question(s)
 

Ok I'm in the process of doing a complete custom rewire while I'm installing my MS3X. When I originally wired the MS harness I only allotted one ground per sensor and one ground for my wideband. Well since then I have added two more gauges that require a sensor ground so I can properly log them with my MS.

My question is will the one 20ga wire I have run to the center console enough to run 3 sensor grounds for my gauges or should I man up and deloom the harness, open up the DB-37, and add two more grounds? Or should I tap into one of the other 4 allotted sensor grounds I have running to the engine and just have one engine sensor share a ground so that I can have at least two 20ga wires to run the 3 sensor grounds I need?

A 20 gauge return wire is fine - sensors don't carry much current.

So each sensor I have on my engine with its own separate 20ga ground wire is over kill then? :giggle: Better over then under I suppose.

Ken and James recommend five separate grounds off the expander board to the main ground.

http://msextra.com/doc/ms3/General_Pix/ms3x-wiring.png




all the sensor grounds should run back to the MS directly (notice the AIT, CLT, TPS, o2, etc):

https://www.miataturbo.net/attachmen...ine=1343236085


and again, a bunch of separate grounds run directly to main ground sport.

I know all that and am very familiar with those diagrams. I have all 5 off the expander to the back of the cylinder head as well as 5 (pins 15-19) off of the main board. I then have pins 1,2,7,8 running to the engine grounding the AIT, CLT, TPS, and CAS respectively. I then have pin 9 run to the center console and was planning on running just a wideband. I have since purchased two more gauges and wanted to know if I need to add more grounds or if I could get away with the one 20ga off of pin 9 I currently have.

That make things more clear?

As Matt said, a 20 gauge return is fine.

The only thing you need to be concerned about is if you have something drawing a lot of current. As a general rule gauges don't. Drawing a lot of current will create a voltage drop across the ground cable, so the reference voltage would be off.
So if you ground the heater for the WBO2 through the MS3, then I would definitely ground that one separately. All other sensor grounds and display grounds can be bundled.

I got that. Matt answered my question right off and made me realize I went over board with sensor returns. Then Brain posted a response thinking I had no idea how to ground anything. I just replied to clarify my actual question.

Thank you for all your help.