I didn't use anything other than what came with the gauge kit.
I put the controller under the dash where the dash speaker used to be.
What I did have to do and I didn't like it, was that any idiot light indication that you want to go to the VHX controller had to be cut, and the wire(s) connected to the controller. High beam, Brake, etc.
In my setup, the only thing the controller gets from the engine is the oil pressure and water temp. But they came with the VHX kit. I don't think I have anything going to it from the ECM or TCM. I could be wrong... the swap was a wiring science project because I kept the original LS engine\trans harness.
I do believe the Check Engine MIL is controlled by the ECM, but I'll have to remember how I hooked it up. The ODBII isn't connected to the VHX controller at all in my setup.
Now that I think about it, I DID wire the E40 computer MIL output to the VHX controller. I get trouble codes, but the CIL doesn't come on... probably because they're not major codes. I'm still learning.
I have to say that the water temp and oil pressure analog gauges are very accurate. As are the digital read-outs. The fuel gauge is another story. Only because that will depend on your chosen fuel tank\sender setup. I set the VHX digital fuel display to blink when the fuel level gets to 10%... then I have very little time to get to the gas station. If it gets to 8%, I'm on fumes.