Yes, as our slightly paranoid friend Jimmy has said (
) , it is most important that everything is dry. Water has a more profound effect on electronics than these old gauges, but as long as everything is cleaned and dry you should be fine.
You need to make sure that all the silt the floodwater has brought in has been removed. This will be nearly impossible with the alternator, heater motor and starter motor, but should be simple enough with the gauges.
Gauges are very simple inside being more related to simple mechanical gauges than anything too technological. You can try flushing them through with clean water to wash the silt out, or you can try heavier cleaning agents like Electra Clean. This stuff may affect the way the front of the gauge looks, and ruin clear perspex so be careful how you apply it. Apply it to the parts you want to clean only, and be careful elsewhere.
Headlights will need to be drained out and washed, indicator lamps as well. The lights inside the car will be fine with a wash out. I would change the bulbs out and spray sockets and connectors with a spray of Lanotec. Lanotec is sheep lanoline mixed with a thinner which protects contacts and prevents corrosion, I use this stuff at sea on communication equipment frequently submerged on the forecastle. It works most excellent.
All the same, they've been wet once, it will not do any harm to wash them out again. The dirt is your enemy, not the water.