Jim Butler wrote;
"suitable wire for 120 volt that will go from the light connection points on the conduit to gauge lights, etc."
I would recommend you reconsider that plan;
I think a 120VAC to 32VAC step down transformer (hidden under the cab floor?) might be safer.
All the wiring out to the the light fixtures, gauge lamps, etc, could be 32VAC (nominally).
The National Electric Code (NEC) has a "breakpoint" at 50 VAC, above that the rules get progressively more stringent. Below that, you can do almost anything that "works".
Otherwise you get into messy stuff like "bonding" / "grounding" / "conduit fill", etc.
And most of your fixtures are likely not rated for 120 VAC. If it's a static display that is "connected" to "premise" wiring and I was the inspector I would want everything "up to code".
With a transformer in an enclosure with a "disconnect" your NEC worries end at the transformer enclosure.
You can get "THHN" wire in many gauges and colors at your local "big box" home improvement stores. It's good for 600 VAC (the next "break point" in the NEC), enclosed locations, "damp" (but not "wet", there is a difference) locations. And it's easy to pull through conduit. Oh, and "technically" you are not allowed to buy "romex" (the common house wiring cable;14/2, 14/3, 12/2, etc.) remove the outer insulation and stuff the bare wires into a conduit. All wire must be marked on the exterior every 36" (?) with the gauge and rated temperature. If you strip the "romex" you remove the markings and violate the code.
Regarding colors; Green Insulation (or some other color with a green stripe, or bare copper) is reserved for grounds. Neutrals are supposed to be white wire (120 VAC), or a wire with a white stripe (can be white electrical tape). Black, Red, Yellow, Blue, Brown, etc. are expected to be "live wires" (maybe switched). These color rules apply above 50 VAC. These rules are so somebody that opens up your work in 20 years has a "clue" about what you did.
Also, the interior edges of some of those old conduit fittings can be quite "sharp", it's easy to nick the insulation on the wire and have a hard to find short show up a few years down the road (well not exactly for a static display). I like to put a few wraps of electrical tape over my wires wherever they encounter a conduit fitting. And they make plastic bushings to "line" the bore of the fittings. I would rather do things once and be done with it.
My two cents (I am a degree holding electrical engineer who has done many NEC complaint (and inspected) jobs).
If I can help, just PM me.
Cheers, Kevin.
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