No oil light illumination on my Plymouth

[WH23G3G]

Ok I had a spare instrument cluster for my 65 Plymouth Valiant I'm trying to get working again. I bench tested it and installed LED bulbs on the spare one. Everything lit up with a battery put to it. The only issue when bench testing the lights was that eventhough the high beam indicator bulb was lit up it didn't even look like it on the outside where the symbol is. I took the old one out today and installed this new one because I wasn't getting any illumination lights or oil light but the radio light was working. So I took all the wires out of the round connector that plugs into the instrument cluster and went one by one plugging them back in. Looks like some were out of order. However when I got to the last spot which was a Dark Blue wire for the fuel gauge and high beam indicator. Well I had already plugged in a dark blue wire in for the oil pressure light/ignition. So the only two wires I had left was a black and possibly a gray or very faint green wire. This harness is not original and may have come from a Barracuda or even a later year. But all but those last two wires appear on the factory diagram I have. The dash lights work now. But the oil light only illuminates and doesn't stay on when you turn the ignition key back and forth from one position to the next, it flickers for a second. Is that a wire crossed or something bad? All the other wires I plugged in were the same colors as were on the wiring diagram except the black and the gray/faint green. So when they're all plugged in right I will have an extra wire. But which one would be the same as dark blue?