Help Please - Hw can I change resistance?

[cts2013]

Good afternoon, appreciate some ones help.
I understand resistance a little but how can work this backwards?
My problem - I have a Volvo Penta Boat leg that registers 430 ohms when the leg is fully down and 740 ohms when the leg is fully up.

My gauge on the boat requires 20 ohms to show the leg fully down and around 150 ohms to show the leg fully up.
These numbers are from my ohm meter with the dial in the 2000 range.

Its way hard to change the potentiometer on the leg, or the gauge on the boat - Is there a circuit I could build to make this all work?

Thank You
Peter

[cts2013]

And I should add. 12 volts DC goes to one side of the gage. It's the earth being adjusted that is moving the needle. Sorry for my lack of a technical explanation.
Appreciate any comments, even if it's a 'can't be done'!
Thanks

[pebe]

Your question is similar to 'Low-power tuned variable resistor' posted in the 'Parts' section of the forum.

It may be possible, but more needs to be known about the gauge. Make? Type?

[cts2013]

Hi, thanks for thinking about this.
Sorry can see no brand marking on the gauge. Its from a USA built Cruiser Boat.
The gauge seems a simple mechanism - has constant 12 volts DC on one side (ignition switch).
The other side if put to earth swings the needle to full down (down to the stop pin).
Using a variable pot on the gauge I can sit it on the down line with 20ohms.
Adjusting to 170ohms swings the needle to fully up.
If I can just get the leg to match these numbers!
Thanks again

[pebe]

OK. How many terminals on the gauge? Where do they connect to?
What resistance will take the reading to half scale?

[cts2013]

Hi, gauge has 2 terminals. One terminal is direct connection to ignition switched +12v DC.
The other terminal goes to the 'pot' on the leg. As the leg rises and full it turns the pot.
Ill check this afternoon re resistance at 1/2 way, also confirm down and up.
I'll post a photo of the gauge etc.
Most appreciated.

[pebe]

Thanks.
What is the resistance of the gauge between the 12V connection and earth?
When you send a photo of the gauge will you show the face of the dial with the 12V supply disconnected, ie. with the needle at rest?

[cts2013]

Great thank you - I'm on it. But cant get back to the boat till tomorrow, will send the data then.
You are from Scotland! Hello from New Zealand.
I'm a mechanical engineer/ex engine builder and been helping a boat owner in Scotland and Wales re their boat engine issues.
Nice to help, and appreciate being helped
Regards