Just got done trying what you said. Put the meter on the wires going to the top of the tank and the meter went all the way over to "0".
If you could drain the tank and then read a bit over 200 ohms, that would tell you that your tank float is working properly for sure. Analog (with a needle) ohmeters have to be zeroed to get an accurate reading, especially on the lower scales. You put the leads together and adjust the zero knob for exactly zero ohms. If you leave the meter on the 1000 ohms or greater scale and try to read low resistance, the needle often looks like it is pointing to zero. On a digital meter, you don't have to zero the scale, but you need to be in the 100 ohm range to get a good reading. If you have an expensive auto-ranging digital meter, then you don't have to worry about any of this.
One other thing to check with the ohmeter is whether you have a short to ground, but from what you said about the gage, I think that is where your problem is and not a ground short. I'll try to look up your part online and see if it is replaceable. I'll get back to you in a later post or edit this one.
EDIT: I checked Messicks.com and found that they have two of the TC33D temperature gages in stock. The part number is 86540853, and sells for $51.59 each. With shipping, that will probably make it over $60. It's too darn expensive, but it's a custom gage. You just have to grin and bear it.
Also, I want to give you a link to my post on where I replaced my temperature gage. The fuel gage mounts in the instrument panel the same way as my gage, so this post will be helpful in showing you how to get the gage out of the instrument panel. Once you have the instument panel out, look at the gage to make sure it is still stuck on full. If so, go ahead and pull it out of the instrument panel and replace it.
Gage removal