Oil light questions

[The Mad Hatter]

Ok, got 2 different cars, both have 1.6L NA engines.  2 different issues.  Any help is greatly appreciated!

1: Possibly the easier problem.  My car (85 Golf 2 door 1.6) will set off its oil light at lower speeds in higher gear.  For example, i can't go 35 in 5th gear (like cruising thru town or something).  If i shift to 4th, the light goes out.  I run 15w40 in the car.  There is a small dent in the bottom of the oil pan, not sure if that's the problem.  It's not a big issue, just annoying.

2: My father's car (87 Golf 4 door 1.6) will have it's oil light start flashing at random.  I can't make it do it under "specific conditions".  We drove it to Alabama (from NC) and it never came on.  But yesterday I'm driving along, been driving for 30 min or so, varying speeds, and it comes on, at 60mph.  No idea why.  Both sending units have been changed, and its not low on oil.  He runs 10w40 in his.

Like i said, any help is greatly appreciated.  Thanks!

[TOW'D]

That differential oil pressure indicator on my "65 Golf was acting up so I replaced the head mounted sender with a electric gauge sender and disconnected that mumbo jumbo smart idiot lights

 I now know what the pressure is by looking at the gauge
I mounted my 3 cheapo gauges by the shifter console
I like seeing what the pressure is not waiting for the light to come on

My pressure at operating temps are 50psi + up to 90psi
pretty impressive for a engine with over 275K KM

a real oil pressure gauge is what I'd suggest
good luck with both