[Mgs] Soliciting advice on an electrical problem

[PaulHunt73]

Ohmmeter is no good, it needs to be voltage when the things are turned on. 
If you have a bad connection then by its very nature it will be variable, 
and what might look good enough with the microscopic current passed by an 
ohmmeter can suddenly get much bigger when you pass real-world current 
through it.  Paradoxically the reverse can also be true, when testing a 
switch that hasn't been used for a long time for example, it can go 
high-resistance over time, lead you to think it is faulty, but will work 
normally when full voltage is applied which can burn through oxidisation.

Points oxidising is a case in point, although in that case they can get 
beyond being 'self-cleaning' when voltage is applied, and need attention. 
I've had a new SU pump and in the box was a slip of paper saying to clean 
the contacts before returning it as faulty.  I've got them going again 
simply by bridging the points with the tip of a screwdriver, which energises 
the solenoid and opens the points, then when they are released they wipe 
together which starts the cleaning process.  A couple of seconds gently 
prodding with a screwdriver may be all that is needed.

You also need to check the earth to the pump is good, by looking for 12v on 
the pump body when the ignition is on.  If you see any voltage there - when 
you have 12v on the spade connection - then the earth is bad, it should be 
zero.

As long as the two ignition whites at the tach are connected together the 
engine should run.  These should have male and female bullet connections on 
later versions (a continuous loop of white wound round an external pick-up 
on earlier), the 12v fed to the tach should be a spade and is not needed for 
the engine to run.

PaulH.

----- Original Message ----- 

> Thanks, that was the direction I started looking at. I checked continuity 
> using an ohmmeter between the 4-way and the fuse box, and between it and 
> the ignition switch (pin #2 IIRC).
>
> I also found 12V at the fuel pump feed. So that is a little baffling. Fuel 
> pump is from car A and was formerly working. Maybe the points stuck in the 
> 2 years it has been out of service.
>