Hello All, I know this topic has been explored in depth before and a lot of good data has been posted. My problem is different and has been this way since I restored it years ago. At idle, the sending unit is putting out about 220 ohms at 35 is PSI. The gauge reads just above zero and increased with rpms. I have read the solutions in regards to putting a resistor in line, but that would give me even less of a reading to the instrument. I had the instruments restored (when I did the car) by a reputable west coast instrument facility. My question is, could it be possible that the instrument was calibrated to an M or E sending unit (which is different than an L sending unit)? Would a quick and easy fix be to use an M or E unit? Any thoughts or solutions would be greatly appreciated. Thanks, Steve
Steve, The gauges are usually calibrated to the normal operating value in the middle of the scale - not to the 0 or max end. Most often to a value around 100 to 120 ohms at the midpoint. Find out if your rebuilt meter is working properly by simply pulling the lead at the sender and connect it with a 100 ohm resistor to ground. It should read somewhere close to the middle of the scale. That means your meter is OK. If you want to to find out which value your meter was calibrated to, just connect a variable resistor to ground. (A small potentiometer of 500 or 1k ohm will do). Adjust it to the point where the meter on the dash points exactly to the indicated value on the scale. Measure the resistance. That is what the sender should produce at the indicated pressure. If the sender deviates too much from that value, replace the sender. If necessary, make fine adjustment with a resistor in series (usually) or parallel (rarely) with the sender. You will probably need to buy a new sender. Dino parts sells a sender with four different thread adapters. Just get the right thread for your car, never mind which generation it was made for. The one I bought a couple of years ago was very good, and required little or no compensation in my M series: https://www.dinoparts.com/en/parts-accessories/ferrari/dino-246-gtgts/electrics/instruments-controls/?p=1 Hope. that helps, Lars
