67 cuda wiring issues

Ok guys, I need some help here. I have a few wiring gremlins I need to get sorted.

1. I need to connect my msd to 12v ignition 'on' but I'm only getting 11.6v from that wire which is a black with white tracer wire at the ignition Switch. 11.6v isn't enough to fire the engine. I have 12.3v at the bulkhead connector inside the car for that same wire. So I am loosing volts Somewhere?
I have replaced the starter relay but same problem. If I hook that msd wire to another wire under the dash that does have 12v such as the cigar lighter positive wire, she starts straight away but obviously it won't turn off with the key.

2. My RH reverse light is not working and RH flasher/blinker is very dull. When I earth the housings on both near where the globes fit, they
work great. It's weird that's it's both RH side earth problems. Do they share earth the same earth wire somewhere in the harness.

3. Fuel gauge not working. I have the pulsating signal at the fitting to the sender which is new.
If I put power to the blue wire from the kick panel, the gauge goes up to full. I've read a heap of old posts about this but....

4. I have dull dash lights at the speedo gauge, but not the little vac gauge in the middle or fuel/temp/amp gauge. I have tested each globe and globe holder. The dimmer works, but they are still dull.

5. At the back of my cluster I have a big red wire and a big black wire that bolt straight to the cluster mother board. Both of these have power. I would have thought the big black wire would be neg and the red being positive??

6. My grounding wires are new and I have the following: battery to chassis, engine to chassis, chassis to dash frame.
I don't have one from the sender to the tank strap and I can't see one from the dash frame to the cluster, I'm not sure where to connect it to on the Cluster.

So apart from all this, everything else works fine. :banghead: