[Mgs] Another Technical Question - Never Mind

[Jack Wheeler]

 Must be the old age thing.  After I sent my previous note, I got to thinking, "What might I have affected when I changed the alternator, that would cause this loss of oil pressure on the gauge".  OK, I did disconnect the wire going to the oil pressure sending unit, but I labeled it with masking tape before I removed it.  Maybe a loose connection? I checked the connection - it was OK.  So, if all else fails, read the manual - right?  The wiring diagram in the manual showed a white wire with a brown tracer going to the sending unit.  The wire I had going to the sending unit was white with a black tracer.  However, there was a white wire with a brown tracer coming from the wiring harness, but it had been taped back by a previous owner, and was not used.  So, what the heck, I tried the white/brown wire and the gauge worked.
The mystery is that I am almost 100% sure the wire I removed from the sending unit was the white/black wire.  Not only did I label it before I took it off, but that wire had a plastic shield around it, like heat shrink tubing, except it was loose on the wire, and the other wire didn't.  Both of these things make me certain the white/black wire is the one I removed.  Why then, after replacing the alternator, the oil pressure gauge did not work, but after switching to the white/brown wire, it did?  Since the wire that was attached to the sending unit (white/black) did not agree with the wiring diagram, I can only assume that a previous owner put the wrong wire on it.  But then, why did the gauge work with the wrong wire on it?  When I discovered the correct wire, which had been taped back, out of use, and hooked it to the sending unit, the gauge worked.
Any ideas of what caused this mystery?  Thanks.
Jack

   ----- Forwarded Message ----- From: Jack Wheeler <jwheeler1947 at yahoo.com>To: Mglist <mgs at autox.team.net>Sent: Tuesday, December 4, 2018, 3:15:17 PM ESTSubject: Another Technical Question
 If it's not one thing, it's another.  I just got my new (rebuilt) alternator installed on my 1971 MGB yesterday, and I have a used door latch on the way.  This morning I started up the car and waited for the oil pressure gauge to come up, as I always do.  But after a few seconds, no oil pressure.  I checked to see that the sump was full - it was.  Since I have had good oil pressure all along, I have to believe it has something to do with the gauge.  I checked all the fuses, and they were all good.
Has anyone had a similar problem, or does anyone have any suggestions where I should look for a solution?  I intend to pull the hose off the oil cooler and crank it over, just to make sure it really does have pressure, but I'm 99% sure that there is pressure - just not showing up on the gauge.
Thanks for your help.
Jack Wheeler
  
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