Problem with gauges

I have a 76 MGB. When the oil was changed, suddenly none of the gauges work--the gas gauge, the oil gauge and the temp. gauge. I looked up in the owners manual but it didn't specify if any of the the fuses work those gauges. Does anyone have any ideas of what could be causing this?

Do you have a Midget or a B model?

I believe it is a B model.

Use a meter or test light to check the terminals that go to the third fuse.
Wiring diagrams are available at http://www.advanceautowire.com click on stock schematics.