Identifying WEMA Gauge

[codingparadox]

On the boat we just bought (Endeavour TrawlerCat 48), we've noticed that the fresh water level meter is funky. It shows full for maybe half the tank and then starts dropping for the lower half of the tank. I finally dug in today and I'm pretty confused. It's following the standard wiring of a WEMA gauge (black = sender, red = power, blue = ground, red+white = LED backlight). However, after I cut the black wire so I can independently measure resistance between it and ground, I'm getting ~320 ohms, which is way off the chart for any resistance-based sensor I know of. We have near a full tank, so if it was a standard US gauge I'd expect near 30 ohms resistance.

The fact that it does, in fact, linearly drop with usage after that half level, all the way down to a nearly empty gauge at a nearly empty tank (visually confirmed at tank), implies that it is working and responding linearly, to something... I checked voltage at the gauge black wire without the sender connected and it's at about 6 volts. Then with the sender hooked up, it drops to ~2 volts, so it does appear to be a standard voltage divider intended to measure resistance.

I also have the problem that I can't seem to access the sender to check that side. At this point I'm guessing it's hidden under the single bed in the office, since I've checked both ends of the tank, but the bed is sealed down with sealant, so I'm a bit loath to try to dig it up just to verify a guess.

So is there something I'm missing? I've read that VDO, at least, has current-measuring gauges.

[codingparadox]

In case other people run across this, I'm guessing that, in fact, this thing is a current-measuring gauge. Something like: https://www.vdo-instruments.com/sens...th-4-20ma.html

No matter what I did, the resistance always sits right around 314-320 ohms standard, but when you apply a voltage to it, it fluctuates nicely. So, I'm back stuck on the stock gauge for now, and someday need to drill a hole in the bed to find the sender to replace it with something less crazy.

[ranger58sb]

WEMA is now KUS USA or something like that. And they make senders in all the various common resistance ranges. Customer service on the phone is generally adequate.

FWIW, our WEMA freshwater and holding tank senders used only two wires, power and ground... and each circuit was fused, something like a 3A (?) blade for each.

-Chris