No one has mentioned Marsden nuts which were developed by a gent named Marsden who worked for Packard, primarily in the marine division. They do not require lock washers. They are the nuts on the bumper bolts in 55 and 56 (G451007 G451011) and perhaps in many other places.

Hi BBCchris
Have you tried the very simplistic method? Take out the unit connect up the electrics. Ensure a good ground point turn on the ignition and get somebody to watch the gauge as you operate the float gently up and down. This eliminates complicated resistance readings.
Good luck
Terry

Well I just renewed the Server Hosting contract for the next year, so PackardInfo is locked in for another 12 months. Now I just have to hide the credit card statement from the wife when it comes in the mail or she will have me living out of my Packard!

Packard sales exceeded Cadillac's in the 1930's. By 1950, Cadillac and Packard sales were about even. By 1956, Cadillac sales far exceeded Packard's. After 1956, neither Imperial or Lincoln's (pre-1970's) sales ever came close to Cadillac's. So while some former loyal Packard buyers might have switched to Lincoln, Imperial, or maybe even a high end Buick, it appears that Cadillac got the majority of them.

Most of us don't realize how much progress there has been (and is still going on) in the development of new aluminum alloys, heat treating etc.

Possibly more than any other material on a car or at least tied with tire rubber.

To illustrate the point. After the fall of the Berlin Wall a prewar Auto Union race car turned up behind the Iron Curtain. It was shipped to England for restoration.

Now this was the most sophisticated race car of its day with an all aluminum, supercharged double overhead cam engine producing over 600 horsepower. It embodied all the latest German technology and materials science.

The cylinder head was ruined and had to be remade. The restorers went to a great deal of trouble to produce an exact duplicate. They had the original material analysed by the biggest aluminum company in England. When the report came back the aluminum company's metalurgist commented "this is the kind of stuff we use for lamp posts and lawn furniture".

Going back farther to the 1920s I recall a comment made by Buckminster Fuller: "There were only 2 alloys of aluminum - soft and softer. I had to wait 25 years before I could get the materials to build the way I wanted to."

This may be a slight exaggeration.

The first efforts I know of to make aluminum pistons were undertaken by W.O. Bentley in WW1. I know he had a lot of trouble making pistons that would not melt or develop blow holes.

The point is making pistons out of aluminum at that time was at the cutting edge of technology and mechanical science.

Loctite will work if you want to use the original fasteners and no lock washers. It does not show or change the original appearance of the parts.

Are you trying to add turn signals and 4 way flashers to a car that did not have them originally? If so there is an easier way to do it.

If you have it off the car, taken it to a sign shop that does painted signs. They should be able to repaint it for you quickly. That is what I plan to do with my wheel covers that need the red background repainted.

Generally 12v relays require a 12v trigger source to switch.

I would think that Taillights would not require a relay as they are not pulling the same type of load that lets say headlights or a horn is. Turn signals are already relayed by virtue of the turn signal flasher.

The headlight relays have merit as it keeps the high load off of the headlight switch contacts, this helps to extend the life of the switch, and it most cases gives you brighter headlights because of lowered resistance.

48 is bimetal & not a typical later resistance unit so readings will be all over. There is a discussion herehttps://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=29603#forumpost29603. I was measuring around 13 ohms on a NOS unit until I assume the contacts changed with the float action and it jumped high.

Assuming the heater element is intact on each end, wiring good and contacts & ground clean there doesn't appear much to repair. About the only moving part is the cam action which flexes the bimetal so it takes longer for heater to open contacts when tank is full. If that is happening, gauge heater should also be on longer and needle should move further.

After this info was posted, someone went and tried a Ford unit as mentioned in the thread. I believe it was for a 30 something on -maybe 37-8-9 and gave the place purchased which was a Ford antique auto place. For the life of me, can't find the thread now but he reported back & said it worked. If you have better luck with search, maybe you can find it if you decide to replace -- wasn't that long ago.