Sounds like Wayne is probably the authority on this specific MS, but I can give you some general background:

All of the "JSx" pins are, at their most fundamental level, raw CPU pins inside the MS which terminate at little holes on the MS board which are labeled "JSx" to match their designation on the schematic, the software, etc.

Now, you can't just take a CPU pin and connect it directly to the outside world. Well, you could, but you'd very likely blow it up. (This is why the JS11 CMP mod bugs me so much.)


Instead, you build a circuit to interface that pin with the real world. For an output, this would most likely be a relay driver, which is documented here, and for an input, a circuit such as that described here.

Dude tell me about it. I've been putting off finishing my GTX engine all morning/afternoon because its cold as hell outside and my garage does not get warm even with a heater.

Thanks for the info Joe that was a good read. I'm slowly starting to understand the fundimentals of how this system works. For the last year, it was basically install it and let the tuner tune and drive the car. But I'm getting a bit more interested in how it works.

Did you get snow as well? We got at least 5cm up here. Super gay. I've got the heaters cranked in the garage right now. I'll give it a few more minutes before going in and braving the cold... lol

I just realized that I need to re-connect my COPS harness before the car will fire. So gotta do that first then I can test if the relay is up and running correctly. Oh, and put all the body parts back on.

Then the only thing I need to do for now is wire the AIT to the ECU. The TPS and IAC wiring will wait until the new engine goes in since it will be easier to access everything.

Ok, so it runs. Drove it around the block a few times.

Now here is the odd thing. The fan is on, but it's on all the time. From the minute I turned the key to ACC it turned on and stayed on regardless of temp.

Another odd thing, I disconnected my IAC valve and my idle was stuck at 2000RPM. I had to turn the screw in to bring it down but it still only went to 1000RPM and no less. I think I have a vaccum leak somewhere which dosen't make any sense since I didn't have one before...

Had some snow this morning that I heard about. It was gone by the time I rolled out of bed at...11:40am lol. Had the kerosene and electric heaters going in the garage and it warmed it up to a toasty 47 degrees (8 degrees C for you crazy canucks)!

Not sure about your fan issue. Something is grounding it. Perhaps try disconnecting the wire at the megasquirt harness to see if that kills it? Did you notice if it was doing this before?

Your IAC valve might actually be stuck open like mine. Mine actually wont idle less than 2k when its unplugged and the throttle stop is all the way closed. I shoved a lug nut in the IAC hose to block it off and just run no valve now. Much better.

You know to be honest, I don't. I don't *think* it was on all the time before, but I can't be sure? I'll dis-connect the wire and see where that goes.

Do you know where the fan relay is located on the car?

As for the IAC, I'll try the plug thing too.

The snow is still on the ground here. Today would have been a great day to hit up the local mountains, if only I didn't feel like a total bag of shit right now. With both my heaters on full blast I can work in shorts and a t-shirt in my garage :D.

JS0 through JS3 are exceptions on MS2 or MS3; they're the outputs for the stepper controller H-bridge, and have enough current to drive a relay or some solenoids directly.