Sam, you probably are using the wrong "telephone" wire. There are lots of different types (I work in the telephone industry, trust me). For wiring & plumbing you need a solid wire (around 26 or 24 awg) that you'll find in CAT5 or CAT6 cable. CAT5 is a 4-pair (8-wire) 24awg, solid, tinned copper wire cable. You should be able to get a spool at Radio Shack.
Now using solder brings up an interesting discussion. Just how big are the air lines on a truck anyway? I would have to assume (dangerous word) that the main air lines from the compressor to the air tanks would be larger than the lines from the wheel lock modulators to the air brake housings. What about the air lines in an air ride suspension? I have a diagram that has the air line as 3/16" ID. Well, that's all fine, well, & good; but what's the outer diameter?