My MS3X is draining the battery
 

'99 with MS3X. Wired mostly according to Frank's instructions.
My wiring in hte attachment.

I used to run it off the stock ECU and the MS3X just running spark, fuel and boost. Now I decided to go for broke and kick out the stock ECU. Almost everything is much better now, everything works (except some trouble with the CEL).

With the MS3 and MS3X plugged in, I'm draining my battery to the tune of almost 3.5A. Unplugging the MS3X and leaving the MS3 plugged in, this drops to ~150mA. Unplugging the MS3 as well gets me down to 25mA or so.

Short of pulling every single connector and checking where the drain stops, is there anything smarter I can do to diagnose?

Did I screw up my wiring somehow?

id double check you wired harness correctly, then go through all the ms3x outputs that go through stock wiring to alternative functions.

do you still have the front and rear o2 installed and plugged in?

Rear O2 is disconnected. I re-purposed the wiring for the boost solenoid since the wires were somewhat close (California model).
Stock front O2 is removed and has been replaced with LC1 sensor. Spliced the LC1 output into the Stock front O2 wire- but just the signal.

What has me baffled is that pretty much all the outputs on the MS3X are switched grounds. In order for them to cause a current to flow, there would have to be something connected straight to battery somewhere on the harness. And I just can't find anything there. It's all switched through relays.

I'm not 100% sure what I did with the CEL, but I think I used JS10, so that would be on the main board and not the MS3X. Maybe it's the Nitrous input- I've never trusted a +12V switch :-)

you can't just use js10.

and you cant use the 12v input for an output...

That may be my problem then. I'll check tonight.

Power to the MS3 is shut off by the ignition switch. There is NO current draw possible when shut off, due to the open circuit. There is no keep alive circuit that draws power when ignition is switched off.

The ECU's current draw is less than 1 amp. If you are reading 3 amps draw with the ignition off, you have something wired incorrectly the MS3, and it's backfeeding through the MS3 when the key is off.

Haven't found the problem yet due to shortness of time, but I believe that I am somehow grounding something through the MS3X that is connected to battery on the other side. Pretty sure the 36W (12V at 3A) are not being burned off in the MS3, since I can't feel any heat emanating from it.

Any anciliaries directly controlled by the MS3 should only be powered by the ignition switch.

You can unplug the Expander. If the draw goes away, at least that narrows down the search to half the pins.

Weird. I opened the case of the MS3 and poked around a bit. Closed it again without changes and the draw is gone.
I guess there's something lose in the harness adapter that got 'fixed' by removing and re-installing the MS3. Couldn't reproduce the problem yet...

Oh well. It's fixed for now.

Possibly a couple of pins on the tyco connector that were shorted or even touched the underside of the MS3 card. The pins are very close to the card. You did use heatshrink tube on all pins?