just had same problem with turn signals and gauges, after weeks of headaches it was something as simple as sanding the terminals at the fusebox! Also had all gauges not reading it was the black wire with the violet resistance wire i mistaken it for a ground, also the post on my gauges were touching the housing
the black wire is for some kind of testing purposes. Wiring kicked my ass ! I I bought a parts harness of flea bay for 40 dollars because my ignition switch connection was melted on both sides and also replaced my ignition switch. A good source for a turn signal switch is Auto part sales in Colorado mfg. by shee-mar( american made) for $72.80 every one else wants over $100 for chinese crap. THis is for a 1970 Mach 1. PS my buddy just put a tranny in a Toyota Solera to save over $500 in labor.