I mentioned this on the fuel changeover switch page: the left-hand fuel sensor on this car has been a problem for as long as I've owned the car (21 of its 36 years now as I type this). It was dead completely when I first got it. Turned out the float had a pinhole and sank. After that it worked for long while. Then it was on the Johnny Carson schedule. Then a couple years ago it just went into permanent retirement. I had to remove it when I drained the gas tanks for the head-gasket job. I probably should have replaced it then, but the head gasket was going to take up so much time and money that I didn't want to deal with the sender too. I verified that the float was okay and not full of gas, hoped that all the handling would free it up if it were stuck, and put it back in and moved on.
That didn't fix it.
I've been putting it off ever since. To remove the sender you have to siphon out the gas or otherwise drain the tank, because the sender is mounted on the back side of the tank well below the normal fluid level. So you either have to purposely run the tank dry (or nearly so), or siphon it, which requires a gas can large enough to hold it. I've got a 1-gallon can and am too chieap to buy a bigger one just for this job. (I do have another can but it's for diesel, and I don't want to cross-contaminate.)
Even then, with the fuel gone, you still have to remove the tail lamp assembly, which I'll grant is pretty simple. But Now For the Hard Part: the sender is mounted on a sheet metal disc that acts as the stopper on the gas tank. There are raised nubs on this disc, and you are supposed to have a special spanner tool that will grab them; you give it a turn and it pops out.
Good luck finding this tool. I've seen drawings of it, but never actually for sale. It is pure unobtanium.
Instead, this is how I get the damn thing out. I took an oil filter wrench (right), the type that fits like a cap over the end of the filter, and bent tabs over to catch the nubs on the keeper ring. The nice thing about this is that it's got a built-in hole to take a socket wrench. It doesn't work perfectly, but it will do. If I can't get it to work, I put a drift punch or a big flat-blade screwdriver on one of the nubs and tap it to rotate the ring counter-clockwise. You risk damaging the nubs this way, so you have to go easy.
I found a new sender for a reasonable price and ordered it. But while I was waiting for it to ship, I found a car at the wrecker and decided to pull one to look it over. Here is it what it looks like inside the car (below left). I've removed the tail light housing and moved it out of the way.
Note that you have to pull two plugs that connect it to the gauge. This is a 12V DC system and polarity means something, so don't get them backwards.
I ordered a new one. It came in a bag. I shot this picture without removing it from the bag--I don't want to open it until I'm ready for installation. You can see the wire is directly connected.
The new sender went in easily enough, Everything works great. I should have just purchased the sender rather than going the junkyard route this time. Tuition.