First MS build, questions to follow.

[toointoxicated60]

So im working on my adapter harness and was wondering what gauge wire everyone else uses.

I ended up using OEM wire and preserved all the wire color codes except MS pin 28 since i didn't have any Red/Blue wire. I used 20 gauge wire for pretty much everything, stock black/yellow shielded cable for the crank sensor(i assume i just ground the shield to any available ground pins on both sides?), pins 32-35 i used 18 gauge wire. What do you guys use?

Also do you guys use plain old heatshrink? I like to use clear adhesive lined heatshrink.

[Jaxx_]

20 gauge is probably good, I think I used 18? and 16 for ignition and high-load drivers.

For the ground there is a sensor ground that is a single ground that should be grounded somewhere else besides the rest of the MS grounds. it's supposed to be separated to reduce noise. You shouldn't ground the shield at both sides, only the originating side. The shielding should go all the way to the crank sensor connector. make sure you twin the wires, which can be done by hand or with a drill. You should run the wire away from other influences of magnetism (spark plug wires, etc)

I use plain old 3:1 harbor freight marine heatshrink. I'm re-wrapping my entire harness in fiberglass shielding soon... But right now getting rid of all the extra wires in the body harness.

good luck.

[nando]

All sensors should ground at ms, do not seperate them. Not unless you like ground offsets.

[Jaxx_]

All sensors should ground at ms, do not seperate them. Not unless you like ground offsets.

I thought there was the seperate sensor ground that came off the MS wiring, which was supposed to be for sensors only?

[nando]

no, there is only one ground plane. use all of the grounds available - 15 of the top pins are grounds. 1-2, 7-19. I think a lot of people just use a handful of them and leave the rest blank.

[Jaxx_]

no, there is only one ground plane. use all of the grounds available - 15 of the top pins are grounds. 1-2, 7-19. I think a lot of people just use a handful of them and leave the rest blank.

good to know when I redo my harness.

[Jaxx_]

From the megamanual clarifying this confusion:

"To start, both the temperature sensors (IAT, CLT) have one or two connections. The recommended sensors have two connections. With these, one goes to ground, the other to the MegaSquirt® EFI controller (the pins on the sensor are not oriented, you can connect the wires either way). With a one-wire sensor, the connection goes to MegaSquirt® EFI Controller, and the sensor is grounded through its body to the engine."

Don't listen to me. ;)

[nando]

that isn't saying anything about ground planes. it's saying you can ground your temp sensors at MS, or through the body of the sensor (like the E30 coolant gauge sensor). grounding at MS is definitely better, because over longer distances resistance adds up, and you get ground offsets and noise in your sensor readings.

there's only one ground plane, there's no dedicated sensor grounds on MS. The wiring diagrams may say to ground a sensor at a specific pin, but they're just giving an example - any ground pin is fine because they're all the same.

Look at any BMW wiring diagram since the m20B25 and tell me one that grounded a sensor somewhere other than the ECU. You won't find any, for good reasons. I'm no EE so I trust what BMW and the inventors of EFI (Bosch) have done for the last 30+ years. :)

[toointoxicated60]

All sensors are grounded at the MS.

I thought it should be grounded on both sides. Why is only one side grounded?

[nando]

ran into this today:

http://www.msextra.com/doc/general/grounding.html

[Jaxx_]

ran into this today:
http://www.msextra.com/doc/general/grounding.html

awesome info, nando.

[toointoxicated60]

Is the stock screen connected at the sensor?

Should i just connect one side of the shielding to ground at the MS for my adapter?

[nando]

it goes to it's own ground pin. if you're using a stock harness with an adapter, just ground all the stock grounds at MS, the shield will already be included. you don't even have to think about it.