I'm in the middle of converting my 715 tank sender and pickup unit. I've cut the top off a 33 gallon tank from a 77 chevy van and welded it into the new enlarged hole in the stock tank. I want to test the sender since it's 30 years old. It should be simple with an ohm meter, but I'm not getting any readings. Either the unit is bad even though it was working a few years ago, or more likely, I don't know what the hello I'm doing when trying to test it. Will someone smarter than me explain a good method for testing this thing? Oh, what is the ohm supposed to be on GM vehicles so I can buy the correct guage too please?