Hi,
I removed some of the interior, amongst other the plastic under passenger side dash. Today I noticed that the ECM and a yellow box(has to do with cruise control?), have dropped down and are hanging under the dash. How are these mounted, stock location? Pictures?

 

Car is an 88 Trans Am GTA

 

I looked around for images but didn't find any. The yellow box is likely the VSS 4-OUT BUFFER box. It is usually mounted to the lower rearward piece of the dash. It sits vertically with two screws up from below holding it in place.

Note that this buffer feeds the speedometer, ECM, and cruise control, so don't remove it.

The ECM will have a plastic holder for it. In '88 it is possible that the ECM has four studs & nuts, or two studs & nuts that fit into slots on the holder. Or, two posts on one side with studs & nuts on the other.

The posts slip into larger holes in the mount. The ECM is vertical with the connectors at the bottom.

As you can tell I'm not positive on all aspects of the '88 ECM mounting. But this should get you going.

RBob.