[Healeys] SU fuel pump polarity

[hspethmann at t-online.de]

My Healey:
BJ8 MKIII 1964
# L27347
pos. earth
 
Fuel pump for the last 20 years:
SU AZX1307
now with a slow, but steady clicking every 15 to 20 sec , when ignition is 
on.
 
I thought, the easiest solution is to change the pump with a spare pump I 
have in my trunk for about the same time as the first one. Both pumps look 
the same on the outside. Both pumps are wrapped in black tape.  But the 
label on the box of the spare pump says: AZX1307 neg. earth. 
In the archives I found a very instructive contribution by Steve Russel 
from Aug 2009. And it ended with the words: "A picture would be worth a lot 
of words right now."
So I removed the cap on both pumps to see if there is any difference in the 
wiring and took a picture, attached to this mail..  Both pumps look the 
same inside. You see the old pump on the left, the new one on the right.  
Under the cap you see a piece that looks like a capacitor, labeled as 
BZX1013. But following the explanation with terminal 1, 2 and 3 clockwise 
beginning with the power input stud and ending with the internal ground 
terminal I suppose the "capacitor" is a diode. But when there is no 
difference in wiring between the old and the new pump, why could it be, 
that the old one looking like a neg. earth ran 20 years in a car with pos. 
earth?
I'm confused and hoping for your wisdom to shed some light on the problem.
 
Best
Achim
 

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