What do all the idiot lights mean on 2001 gmc isuzu 3400 diesel - especially the one in the center that looks like a goal post for football, with 3 verticle bars above the goalpost cross bar?

IDIOT LIGHT
A derogatory term for an instrument panel warning light. They're called idiot lights because they're for idiots who don't know how to read or understand gauges. Actually they're not all bad. An idiot light won't give you any indication that a problem is developing until it happens. On the other hand, a light commands more immediate attention than a gauge. The "ultimate" instrumentation should include both: gauges to give an accurate indication of coolant temperature, oil pressure and charging current, and lights to catch the driver's attention when readings approach the "danger zone."