Hi joe o,
have same problem with hyster 5-ton, after changing hidraulic tank cap, the 676-4 error appeared. Wiring from glow plug relay to vsm is good, fuses are not blow. Relay gets low voltage from vsm (aprox 8.5V - measured on relay pin and directly on output pin on vsm, so the wirings are good). Any solutions?

If you have no power at glow plug relay... wire 240-a comes from a 60 amp fuse coming from the starter battery post. Could be blown fuse or wire issue. Wire 754-0 also positive voltage comes from the vsm. If no power there, could be broken wire between relay and vsm, could be wire loose in plug. As to the codes for dash entrance, not at liberty to disclose that information.