I'm going to mod the existing oil pressure guage (which is effectively only an idiot guage, it's either on or off) by replacing the sender and jumpering the resistor, as described elsewhere.

Looking for ideas to put an additional idiot light for warning.

Options:
Use the existing pressure switch, add a relay (to switch the OK-is-on signal to low-is-on) and

1) stick a light or led somewhere

OR
2) figure out how to light up the existing Check Oil lamp in the dashboard. Anyone know how to access that lamp?

Thanks.

'90 Ranger Extra-Cabl XLT w V6 manual and 227K miles
No oil burning since the head job!

 

The check oil lamp in the dash is just to show you if the oil quantity gets very low. Otherwise it will stay unlit.

 

You could put a "T" fitting in place of the sending unit, move the old sender to one arm of the "T" to operate your idiot light & connect your real oil pressure sending unit, for the gauge, to the other arm of the "T".