FIGJAM wrote:Red is+, black is-.
In AC wiring, white is neutral, green is ground, black and red are hot. Often black and red are opposite sides of a 240 volt circuit.
In newer solar and DC installations, white is generally negative, red or black is positive.
In older DC installations (car stereos etc) red is + and black is -.
What all that means is that you sometimes can't trust the colors, but there are some general assumptions you can make.
Most RV generators are 120VAC, which means there will be one hot, one neutral and one ground. The hot is generally black or red, neutral is almost always white and ground is green (often with other colors striped in.)
TT-30 plugs are 120VAC 30A plugs, so you will end up with 3 wires that are doing something. (The 4th wire is either disconnected or is connected in parallel with another wire.) To verify this borrow or buy a multimeter (they're only $10 or so at Radio Shack) and measure resistance from black to red. If it's zero they are connected together.
From your description the most likely connection scheme is:
Your old cable The new cable
(nothing) Red - just tape this one up and don't connect it.
If there's no green wire in your old cable, connect green to the RV chassis. If the red/black options aren't making sense it is sometimes OK to connect everything together (all reds and all blacks.) This is always OK on 120 volt only systems since both have to be at the same potential, and the TT-30 can't carry 240VAC anyway. If your RV load is expecting 240VAC, and you connect everything together, then all your 120 volt loads will work but your 240 volt loads (A/C?) won't - but they won't be damaged, they just won't turn on. The only time it is NOT ok to connect red to black is if you are using a 240V source. If you do that the circuit breaker will blow pretty much instantly.
If you are planning on connecting your RV to a generator it may be easier to just buy a 12 gauge extension cord, cut off the female end and wire that one in. That's guaranteed to have three wires so connection might be simpler, and most generators have a standard NEMA 5-15 or 5-20 plug (i.e. one that looks like it's a regular wall socket.)