Gauge of interest

The sender is turning out to be a little less cut-and-paste than I'd hoped.  Most of it has to do with the difference in form factor, as might be expected.  Turned out that I'd actually have to cut some spot welds to get a workable solution in place, providing me with a stopping point last night because of concerns about volume and waking people up.  All that kind of stuff.

While this means I don't have the sender completed and installed, it also means I at least have a good idea of where things need to go from here.  The plan will make more sense once I've got you caught up on the other details, though.

First thing first, I wanted to check if the sweep of the new rheostat lined up with the '78 sender's sweep.  This came first because I was almost certain it wouldn't, so wanted to get that out of the way before I started trying to get smart.  As the picture below shows (left), it doesn't match with the pivot points centered.  I decided to check it against the pre-'78 sender (right), and found it was even further off.

With that confirmed, my next thought was to see whether I'd be able to trim the new resistor strip to fit the original sender's rheostat housing.  Here's a comparison of lengths.

I figured I'd have some excess I could trim, since my read of the resistor value at max resistance was a little over 270 Ohms.  I measured the strip for the desired range (between roughly 30 and 250 Ohms) and found that the winding pattern used didn't allow for me to trim off the 15/32" or so that would be needed for the board to fit without sacrificing a fair amount of resistance wire and usable gauge travel.

Left: point where R value is approximately 30 Ohms.
Right: point where R is slightly over 248 Ohms.

At that point, I had officially ruled out all easy answers.  I wasn't going to be able to effectively transplant the rheostat assembly or resistor strip into the '78 sender and the sweep was all wrong for the older sender (which wouldn't have been as easy, anyway, since I would need to further modify it to work with my '78 tank). 

As I was getting ready to shut things down for the day, I took one more look at the sweep of the new sender against my '78 unit.  I found that, by lowering the pivot point about half an inch, the sweep actually did match.  Having figured that out, the plan is to cut the backing of the rheostat housing off its mounting strip, then trim the housing on the '78 sender to accommodate the new one.  I'll have to make some adjustments to the float arm to compensate for the different pivot point, but I think it should work out alright.

That's all going to be done later, though.  Right now I need to finish this radiator and cut the exhaust down.