I have a 96 T/A that I what to put a manual fan switch on.
I converted the car to OBD1 a few years back and all is well.

I been looking at the wiring schematic instructions from shbox.com

http://shbox.com/1/fan_sw_diagram1.jpg

This where I'm at with this, because I have converted to OBD1
I should use the OBD1 instructions. Yes/No


I tested terminals H and J without the car running this afternoon
using my Powder Probe by applying ground.

This is what I found.

Ground terminal J "low speed" both fans run on low.
Ground terminal H "high speed" only one fan runs on high,
"the passenger fan"
Ground terminal J and H and both fans run on high.

Is this how this system should work? Ground J and H for both fans on high?

 

Yes. You have discovered the medium air flow speed with terminal H alone, that isn't used by the pcm. Most folks don't know it exists.

 

So my findings are correct? The PCM just adds H to J for high speed?

 

Once again...Yes.

 

That's exactly the way the DPDT switch in Shoebox's diagram is wired.