Which grounds to use where.

[WELDER]

In my MSII wiring harness, there are the standard 6, black grounds.

As per the megamanual, pins 8,9,10,11 and 18 are to be grounded to the same lug. Leaving the ground from pin 19 for sensor grounding.

My question is, does pin 19 HAVE to the sensor ground?

I am trying to get around taking my harness apart, as it is heat-shrinked at the clamshell from DIYAutoTune.

Thanks in advance.

[Bernard Fife]

Welder,

There is nothing special about pin #19 on a V2.2 or V3 main board, it joins the others at the DB37 on the PCB. However, it is important to have a separate wire for the sensor grounds, so the the internal circuits aren't fooled by the high currents (and resulting voltage offset) from the injectors (and possibly ignition) passing through the same wire.

Lance.

[WELDER]

Sounds good.

Looking at the V3.0 diagram (http://www.megamanual.com/index.html), should the O2, fuel pump and main relay be grounded to the engine, or is the negative terminal on the batter good enough? I was also wondering the same about pins 8,9,10,11 and 18; should they go to the engine ground or - on the battery?

I apologize for the newbie questions, just trying to figure out the basics.

[trakkies]

Sounds good.

Looking at the V3.0 diagram (http://www.megamanual.com/index.html), should the O2, fuel pump and main relay be grounded to the engine, or is the negative terminal on the batter good enough? I was also wondering the same about pins 8,9,10,11 and 18; should they go to the engine ground or - on the battery?

I apologize for the newbie questions, just trying to figure out the basics.

The fuel pump should be connected via a relay. So where the actual pump ground is won't matter to the MS.

[WELDER]

Sounds good.

Looking at the V3.0 diagram (http://www.megamanual.com/index.html), should the O2, fuel pump and main relay be grounded to the engine, or is the negative terminal on the batter good enough? I was also wondering the same about pins 8,9,10,11 and 18; should they go to the engine ground or - on the battery?

I apologize for the newbie questions, just trying to figure out the basics.

The fuel pump should be connected via a relay. So where the actual pump ground is won't matter to the MS.

Fair enough, thanks!

As for the relays (excluding the FIdle relay) in the diagram, it it best to ground them to the frame, engine or back to the battery?

[twofouroh]

Grounds arent really that complicated, you just need to make sure you get a good ground! Start at your battery, and make sure that it is grounded to the engine and frame really well. I always make sure I have a bright metal connection on both. After that, generally, you would ground to the nearest factory ground point, or just make your own close to where you need it. The only exception to this rule would be sensors, which are usually using resistance bridges to create an output voltage. Ground these to the sensor ground at or near the ECU, and never to the block, since it sees high current through its ground, and some high voltage thru the plugs. These make for potential ground offsets and voltage spikes, so the block is not a good signal ground, but should be fine for relays and other 'output' type devices. The MS has a dedicated ground wire for sensors (pin19), so connect all the 'input' device grounds ( TPS, CTS, IAT ) to that wire INSTEAD of the frame, block, etc.

Hope this helps

[WELDER]

Thanks twofouroh.