[FortyNiner]

The issue with many of the older units is with the rear lights. Seven wire systems were designed to allow the rear factory housings (with dual filament sockets and bulbs) to provide turn/brake/tail lights. Lesser set ups (those with 4 to 6 wires) need either additional light set housings on the rear or the installation of several relays to support all those same functions. Finding a schematic is a Google search. With the schematic, testing isn't a big deal.