Do a Step by Step anylysis like Dave mentioned above, followed by my additional proposals.
This will help you exclude things to finally encounter the guilty one. Many things could affekt engine running, also false air, control pressure and much more.

Beside water damage, ECU themselfes can fail also due to flawed capacitors where after after 40 years thats normal. I checked many of them which where not proper working anymore and often a replacement of the ECUs whole internal electronic to a CPU based one beside makinge problems going away even enhance the process of lambda control and therefore optimize the air/fuel mixture generating.

When you unplug said relay or the interior light fuse, does the idle drop and get rough, or stay the same? Should drop if the system is working.

so with the relay unplugged / interior light fuse removed, it does run rough.

It starts up fine and runs, but no feels like no power. FV appears to be working everything else checks out, could it be the ECU or a fuel injector causing the miss or rough running?

Have you verified if the FV is indeed vibrating? It's an audible buzz, which you can also feel by touching it.

There's a way to turn it on without starting the car by unplugging one of the connectors to the throttle body behind the airbox - someone please correct me as it's been a few years since I did this.

I ask as I had this exact same issue with my SC. I neglected to check the FV buzzing which it indeed was not working. Turned out I had a burned lambda ECU that prevented it from functioning properly. Replaced the ECU and all was well again.

my exhaust is pretty loud, so Can't be 100% sure its working. That said, as I was reaching around I noticed that my injectors seem loose at least a couple of them. could that be a problem as well? I think I will have my ECU rebuild, can't hurt its 40 years ol

Jason, this is what SkunkWorks is refering to:

http://forums.pelicanparts.com/uploa...1642194561.jpg

Its a bit difficult to reach but its possible. Disconnect the plug and just turn the key before its position where the starter turns, means current reaches the fuel pump relay.
With the plug above disconnected the fuel pump safety circuit will be off and this will make the fuel pump on the front and the FV in the engine compartment buzzing as it gets its current via the fuel pump relay.

You also could brindge specific terminals in the fuel pump relay socket but the method above is more newbie proof.