Chris,

If you have noticed my posts to the 850 yahoo group, you know I believe I am experiencing low oil pressure (warning light in dash comes on and only goes out at high [increasingly higher, though not exactly consistent] rpm).

yes, I saw them, but didn't respond as it seemed like it was getting covered.

One reply to my posting indicated that perhaps my sensor is faulty. I think I will start there before dropping the pan and getting into the oil pump.

Is this the part I want to replace?

0004151890 N A 850/2100 COUPE/SPIDER LONG OIL PRESSURE LIGHT SENDING UNIT 7.75

That might be a good idea. However I always like to troubleshoot before just swapping out parts. If I had the car for service I would connect a mechanical gauge temporarily to see what was really going on. But the light coming on as you describe can be attributed to this switch being faulty.

Also, the light has always worked, the gauge, however, is another story. Since I have owned the car (going on 2 yrs) it has indicated low pressure at startup (sounds normal enough), then, at a time when you would expect the pressure to be coming up to operational levels, it drops to basically the "off" position.

That is because the diaphragm rips internally, so when the pressure equalizes on either side of the diaphragm it will read zero.

Will the above part remedy that as well, or is that a separate component? If so, how much for that one? Also need whatever gaskets/washers are needed for this replacement.

No, for the gauge sender use 5972876 $39.50 The gaskets you'll need are two 10298460 at $1.00 each.

Any chance a stuck oil pressure relief valve would cause low pressure as I have indicated? Thanks as always for your invaluable information and time!
Rodney E. Bender
'67 850 Spider

Yes, the oil pressure relief valve might be stuck if the piston is sticking in the bore, or if some previous idiot has attempted to fix the low oil pressure on the gauge or the light on at hot idle by stretching the spring. The oil pressure relief system is right there on the side of the motor, so it's easy to pull it and inspect/test.