I have an original Prodigy from 2003 that's been used on 2 trailers and 3 tow vehicles. The P2 or P3 are the best bang-for-the-buck.
Grab that P3 and cable from wtxdxer (send Alan a PM). These have no moving parts internally, so there is very little that can go bad on them, compared to the types with mechanical pendulums, etc.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller