Spare GND pins 8-14

[hiltonlo05]

Building my harness and got an embarrassingly basic question...

How many sensors can share the sensor ground line (pin 7) on the harness? The manual shows pins 8-14 as spare gnd, and it looks as though I've put black wires in all those spaces (not sure what I was doing). Can all 15 something sensors come back to pin 7 or do I need the spread them out over 8-14 and tie then into 7 (sensor ground) inside the ms3 case?

[kjones6039]

or do I need the spread them out over 8-14 and tie then into 7 (sensor ground) inside the ms3 case?

Pin 7 is already common with all the other ground pins inside the v3 case (board), so you don't need to "tie" it to anything.

Ken

[hiltonlo05]

Ok, hated to ask a stupid question but being cautious on my first build.
Thanks!

[billr]

Is this an MS3Pro, with grounds only up to pin 14? MS3 has grounds from 7-19...

[hiltonlo05]

MS3X from DIY Autotune.

[hiltonlo05]

The "confusing" part was the manual calls some grounds POWER GROUND, SPARE GND, SENSOR GROUND. I'm just being overly cautious in case it made a difference.

[Raymond_B]

The "confusing" part was the manual calls some grounds POWER GROUND, SPARE GND, SENSOR GROUND. I'm just being overly cautious in case it made a difference.

But it's important to know the **difference** in those labels. Just because they have ground in the name doesn't mean they are all the same. In the case of sensor ground, yes ALL sensors must ground to that pin. The manual is pretty clear on that.

[billr]

I'm going to offer a dissenting opinion: all the ground pins on the MS3 mainboard are tied together internally and are functionally identical, any can be used for any "grounding" purpose. Note that you have five more to use, 15-19.

[kjones6039]

I'm going to offer a dissenting opinion: all the ground pins on the MS3 mainboard are tied together internally and are functionally identical, any can be used for any "grounding" purpose. Note that you have five more to use, 15-19.

Absolutely correct! As I attempted to point out in my post above...............

Ken

[billr]

Yeah, I know Ken. Figured I would give it a try...

[kjones6039]

I certainly wasn't chiding you Bill!!! Thanks for re-enforcing my original point!

Ken

[Raymond_B]

No way I am going to argue with you guys, you know way more than I ever will. It just seems there has been a lot of distinction between ground and signal ground.

[kjones6039]

No way I am going to argue with you guys, you know way more than I ever will. It just seems there has been a lot of distinction between ground and signal ground.

NP Ray! I promise you that this is one that you (and the op) can take to the bank!

Ken

[hiltonlo05]

I absolutely understand the importance of signal ground vs power ground...however, what was the spare gnd intended to be used for? The manual color coded diagram doesn't show them being connected to anything, so are they spare power ground or spare sensor ground?

[DaveEFI]

I absolutely understand the importance of signal ground vs power ground...however, what was the spare gnd intended to be used for? The manual color coded diagram doesn't show them being connected to anything, so are they spare power ground or spare sensor ground?

Personally, I'd not add anything which needed a power ground to MS. By all means ground it to the same point - but not through the MS PCB.

[hiltonlo05]

I may have worded that poorly...I don't intend to ground anything thru the ms3, the original thing that spawned the question was that I have about 12 items that require sensor ground, and was concerned on how to get that all back to the ms3. I'm tieing al the ms3 power grounds together and taking them directly to the engine block.

In general, is it an ok wiring practice to splice sensor grounds together throughout the wiring harness and only have say 2 or 3 wires that come back to the pin 7 on the db37 connector? For example, TPS, MAT, and fuel pressure sensor are all in close proximity, so can I splice (solder and heat shrink) them all together and just run 1 wire from the manifold back thru the firewall to the MS3?

[billr]

^^^^ +1 on the reply from "DaveEFI"
(Ken, I did not think you were chiding me, was just acknowledging your previous advice)

[billr]

I would avoid having the CLT or MAT share a ground wire with any others. Others, like the MAP, FPR, and TPS are less likely to be a problem, but why risk it? You don't need big wires for those, 22 AWGwould be very "robust" and a bundle of those takes hardly any space and can be quite flexible. Put them in a loom with the rest of wiring and they won't ever be noticed.

[hiltonlo05]

Bill,
I agree, it's not a huge problem to do and I'm not in favor of taking unnecessary risks. So once I bring all those individual wires back into the car, it's ok to tie them all together say 3 inches from the db37 plug and then 1 single wire into the pin 7 on that plug?

I know these are basic questions, but just trying to thoroughly cover my bases.

[Raymond_B]

Bill,
I agree, it's not a huge problem to do and I'm not in favor of taking unnecessary risks. So once I bring all those individual wires back into the car, it's ok to tie them all together say 3 inches from the db37 plug and then 1 single wire into the pin 7 on that plug?

I know these are basic questions, but just trying to thoroughly cover my bases.

They are good questions and a good discussion. I had a misunderstanding that was cleared up so thank you. I had been planning on using a marine type busbar to bring all my under-hood sensor grounds to one spot and then a single wire through my bulkhead connector to the "sensor ground" pin on the MS. I was going to connect all the "ground" MS pins to another separate busbar that would connect a heavy gauge wire to the engine block.