1994 Mercury Cougar.. gas gauge don't work.

Did you check the fuses?...doesn't work?...not at all? you could put a multi-meter on the connector what leads to the tank...or pull the connector off of there and measure the voltages there with the ignition key on and off to see if it's powering up....'nother trouble area could be your gauge (dashboard)...what makes you think that the dash panel is okay? You might think about renewing the chassis ground with a wirebrush to the battery 1/0 cable at the chassis...a lot of times electrical problems can stem from this "iffy" connection~

...and a BRAND NEW battery as 10% per year the thing will not take a charge...so if it's an OEM...you're asking grampa to take your barbells to the attic~

It's usually the sending unit in the tank. You can unplug the sender and short the wire to ground (orange wire I think) and watch the gauge go to "FULL". Typically, if the rest of the gauges work, it's the sender in the tank. You could get out a volt/ohm meter and check voltages and continuity of grounds BUT: if the electric fuel pump operates then you KNOW the ground circuit is in tact. Be sure to drive it until the tank is as empty as you dare before pulling it to change the sender. It's much easier that way.

My speedometer;tachometer and gas gauge doesnt work since someone was checking fuses under the hood.

my speedometer does not work