[Mgs] Another Technical Question - Never Mind

Steven Trovato strovato at optonline.net
Tue Dec 4 14:59:00 MST 2018


Jack,

Check out this link:  https://www.mgexp.com/article/lucas-colours.html.

It shows the white with brown tracer as oil pressure gauge and white 
with black tracer as ignition coil contact breaker to distributor 
contact breaker, or distributor side of coil to voltage impulse 
tachometer.  I  would want to check both of those wires and see where 
they really go.  Does your car have a tachometer that should be using 
that wire?  Is the tachometer working?  I don't know how the oil 
pressure gauge would respond to the tachometer input.  It would be 
scary to think that you weren't really reading oil pressure before 
and the gauge was just responding to the tach signal that says the 
engine is turning, I don't really know if any of this is 
plausible.  I am doing a lot of guessing and speculating.  I would go 
back to what I said before, check where those wires really go.

-Steve T.


At 03:57 PM 12/4/2018, Jack Wheeler via Mgs wrote:
>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


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