Oil pressure sender

[MAXcuda]

I changed over from a standard to rallye dash, and I swapped out the oil light switch for a sender specific to the gauge.  Now I paid to have my gauges calibrated when they were restored, so I assume the gauge is in spec.  The oil gauge always reads very low (zero to 1/4 range).  It scared me real good when I first looked at it.  The idiot light used to flash on and off rapidly at idle.  I hooked a mechanical autometer gauge to it and read 16-18 psi at idle and all the way up to 40-50 psi around 3000 rpm.  This is on a '70 340, mileage unknown.  All of the other small gauges work fine.  Its getting 5V continuous power from a voltage regulator chip-circuit I built to replace the old points voltage limiter.  This is the "correct" sender according to the computer at Advance auto parts.  You know how that goes.  What should I do?  Is there somewhere I can order another sender that is definitely the right part?  Or is there just no hope for ever reading an accurate, semi-reliable oil pressure from crappy stock gauges?  (regardless of what they may sell for on ebay)

[OUTLAW]

If memory serves me right the oil pressure guage works on resistance so as pressure increases the resistance (compared to ground) decreases causing the guage to rise. To make sure ground the lite wire to the block and see if it pegs out the oil pressure guage or drops it to zero . in any case you can add a resistor in line between the sending unit and the wire to adjust the needle to where you want it to read for peace of mind

[Chryco Psycho]

the guage can be recalibrated & restored , or try a second sending unit

[OUTLAW]

I think he already had them recalibrated but CP is right try another sending unit we have a saying around the shop " just because its new doesnt mean it works right " as a last resort use the resistor to make it read on the guage where you think it should be ...this works with most electric guages as temp guages are often off too

[MAXcuda]

i believe the gauges work as you said, decreasing resistance as oil press increases.  this causes a greater current to flow, heating up the metal strip in the gauge more. so putting a resistor inline will increase the resistance and lower the reading further.  do you mean i should put a resistor in parallel across the gauge and ground?  i may also just try a new sending unit. 

[Katfish]

I have exactly the same problem.  But both my gas gauge and oil pressure were low.  I built an adjustable voltage regulator to put out 5.3V instead of 5.0V.  This fixed the gas gauge problem but the oil pressure is still low.  I think the problem must be on the sending unit side.