First thing to do is check wether you have no positive supply or no earth.
So Turn on your dash lights and check for 12vdc Positive on one side of
youre dash light somewhere with a multimeter....ie a plug or bulb holder...Ground the neg lead tfrom youre meter to a known good earth..If you have 12vdc Positive then youve lost youre earth, somewhere common for all bulbs/lights on dash. Check the otherside of the plug / bulb holder for an earth by setting youre meter to continuity and see if you have an earth. It can only be one or the other....
No positive with good fuses is usually a broken wire in a harness. Maybe rubbing on a sharp bend or pinched too tight by a clamp/cable tie..etc
Bear in mind that this is assuming no inline relays or dimmers are in the wiring which may have failed.
No earth can be simply a common earth bus, rail, tie off point, that has come adrift or needs to be reseated due to a bad earth.
Always start from the battery and work youre way along checking for 12vdc Pos as often as possible ie..back of plugs etc..untill youve got youreself all the way to the dash light themselves.
Hope this helps.
