Gauge woes (trim & temp)

I bought this gauge from great lakes skipper: http://greatlakesskipper.com/produc...fuel-temp-trim-volt-boat-gauge-wout-logo.html Since most of GLS's stuff is OEM overstock and what not, there is no documentation. The volt gauge and fuel gauge work fine (as they are pretty much standard). However, I've got some issues with the trim and temp gauges.

The trim gauge reads backwards (up when down, down when up). From what I understand, Merc trim senders are backwards from OMCs so I guess that's my issue. Knowing what I know about electricity, this being a resistance measurement, it's not like I can just "reverse the polarity" or something. Anyone got any ideas on this? I think I'm screwed on that one.

The temp gauge reads way low. I've got this sender http://www.iboats.com/Mercury-Temperature-Senders/dm/view_id.271503 (or similar). When connected to my ohm meter, it measures resistance, and changes quite a bit when heated (with a lighter). However, the gauge only climbs to like 120 or 130 tops when heated with the lighter. (when run with the motor I don't think it ever even gets to 100 even). Can I add resistance to the circuit or something to possibly make this accurate?

Re: Gauge woes (trim & temp)

The temp gauge you have requires a sender with 30 - 240 ohms resistance. Measure the resistance of the sender you have. Cold should read 240 ohms and hot should read 30 ohms. No -- you can't add resistance as that represents a fixed value in addition to the existing value which would make the reading worse than it already is.