If you have a freightliner chassis I think the dash gauges get there power from the gauge (I might have the wording wrong) module. The module is part of the enunciator panel with all of the warning lights. The power goes thru the light switch, then thru the dash lamp dimmer (may be part of light switch or separate like mine) then thru the guage module then finally to the guages. If some guages light then there is nothing wrong with the light switch, dimmer or fuses. With three guages out I dought that the bulbs are burnt. You may have a wiring problem or guage module problem. Do not use a test light (to much current) use a digital volt meter and check for power to each guage. Again, if you have a FL chassis, you can remove the guages from the front. Just twist the guages bezel a quarter turn to remove. Under the bezel you will find two small cap screws to remove guage.
Dave and Laura & two cats
02 Discovery with Accord toad
retired auto rv tech and teacher, wife rt nurse