If "no change" means that the only issue is dash lights not working, that is a very small issue. Easy to troubleshoot and does not require a harness. Be sure that is the only electrical issue, then we will help fix it.
It seems you are buying parts and have not done proper checking.
Don't know what you mean by other wires being "upgraded". Generally speaking, if 6V wires are OK, if insulation is not all dried out and cracked, they are just fine for 12V.
It could be you have the headlight knob rotated CCW. That may dim dash lights to almost off.
1. Who did the 12V conversion?
2. How did you know the dash lights were 6V bulbs? Were all the filaments burnt out?
3. How did you find 12V bulbs so fast without asking for a number?
4. Do you have the dash disassembled?
If you have any more trouble, as a person who is new to electrical, you need to ask before acting. We started out by advising to change to 12V bulbs and after you did that you moved on alone instead of reporting back. This is not usually a good way for a novice to work. But as you said, you can figure things out.
