Still battling my no start and oil light mystery

[WH23G3G]

This problem is still my 65 Valiant. Ok I looked at my 73 Charger's oil light system to get familiar with how it might work on my 65 Valiant. I assume they work the same. I thought maybe the oil light on my 65 Valiant may not suppose to be lit up when you turn the ignition key to ON. But it does on my Charger. The only activity I can get from the oil light is a flicker on the dash when I turn the key from run back to OFF position. Nothing happens between OFF and ACC. I've checked and rechecked my wiring to the round plug on the back of the instrument cluster thinking I have the wires in the wrong spot so I even tried every possible way and nothing changes. I pulled the donor harness out of a 64 Valiant so there is an extra wire on the back of the plug that is a very close color to the gray wire for the oil light, so I switched them back and forth with no change. I unplugged the wire from the sending unit under the hood and connected a jumper to a ground to see if I could get it to light up and again nothing at all. I noticed 3 of the spade terminals going through the bulkhead firewall connector were not pushed out enough through the bulkhead so I figured maybe that was causing the no start and oil light problem. But it didn't change anything. All the lights and signals work. The radio doesn't turn on but that's probably because there's no antenna but the light works. The heater fan doesn't turn on either, but I don't know if the switch was bad to begin with. The worst thing is I can't even start it with the ignition key. I must arc the starter relay under the hood. All the electrical components are new. Even the forward light/engine harness is new. There's no sound at all when you turn the key to start. I'm figuring the no start and oil light problem have to tie into the ignition because they all work off the ignition switch. What's happening when I turn the key from the ON position back to OFF, in between there is when the oil light just flickers on the dash? Is it a bad ground? If so where is the common ground these two share? I tried jumping the neutral safety switch and tried in all gears and nothing happened with the key either. There is an extra terminal on the back of the new ignition switch and I tried running a ground wire to it and nothing changed. Any ideas?

[Chryco Psycho]

the start issue is one of 2 things , have some one turn the ign switch & see if you have power to the yellow wire at the start relay , if you do then either the relay is bad typical or the brown wire from the relay is not grounding at the trans assuming it is an automatic , this can be a bad NSS switch or a bad plug at the trans . if you run a jumper from the brown wire terminal on the relay to ground & urn the kay & it starts the NSS switch or plug is the problem  , if not the relay is bad .
The oil sender should have power into the light & the wire from the light [usually grey] goes to the oil pressure switch , there are 2 types of senders , a bell shaped pressure gauge & a smaller switch so you could have the wrong sender in place , , when you ground the grey wire the light should come on but it is not so you need to check for power at the light & see if youhave power there then see if youhave any power down the grey wire

[WH23G3G]

I went over and worked on the Plymouth today because it was nice out. Trying to figure out why I can't start it with the key. I took the instrument cluster out and checked the pins on the back of the circuit board. The one for the oil pressure light was coming apart but all I had to do is squeeze it back together with pliers. But I swapped the whole board out with another one I had. That didn't fix the oil light problem. I replaced the starter relay on the firewall again but it didn't change anything. I tried again to put a jumper wire on the Ground terminal of the relay and tried starting in any gear but nothing changed. My last idea was to remove the entire dash harness and make sure there is no breaks between the ignition switch and the firewall connector. The wires were totally intact not even and chaffes. I verified once again that the colors of the wire were in the proper location on the bulkhead connector and secure. Again they were. I have an extra light green wire going into the back of the instrument cluster round plug that goes to nothing. So I put it in one of the empty slots on the back of the plug. The color on it looks very similar to the gray wire for the oil pressure light so I verified that the one I have plugged into to the oil light location goes out to the bulkhead connector for the oil switch and it did. I do need to see if there is power at the relay when I turn the key to run. Is that how you do it? Have someone turn the key like they were starting it and probe the yellow/black tracer wire on the relay with a test light? Does the yellow wire/black tracer stay plugged in? Can I do the same with the gray wire for the oil pressure light? Have someone turn the key and probe the gray wire on the bulkhead connector and the test light should light up. I've been trying to figure this out for months. I'm almost ready to just replace the whole dash harness with a new one but I don't think the car is worth $550.