[Mgs] Soliciting advice on an electrical problem

Max Heim mvheim at sonic.net
Mon Jul 23 11:53:55 MDT 2018


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.

I may need to check the white wires at the tach, since they had been cut (assumption was that it was to reverse polarity) — perhaps I put them together incorrectly.

It had been a long day and I was getting too tired to deal with it in a systematic fashion. I will attach it afresh at the next opportunity.

--
Max Heim
mvheim at sonic.net



> On Jul 23, 2018, at 12:48 AM, PaulHunt73 <paulhunt73 at virginmedia.com> wrote:
> 
> From what you say you are largely on your own, except to say that you need 12v at all the points shown on the standard wiring diagram for powering the pump, ignition warning light, ignition and starter.  If you have a standard harness it can't be that different from the factory diagrams.  If you have the warning light and it cranked you know the ignition switch itself is OK.
> 
> Next thing is the pump, and that is a matter of locating the white wire to the pump in the rear harness where the mass of connectors are in the engine compartment, and seeing if you have 12v there from a white in the main harness.  That should be in a 4-way bullet connector, two whites in the main harness, one is a supply wire from the ignition switch and the other goes on to the fusebox.
> 
> Once you have a pump, and it cranks, next thing is ignition.  Prior to 1973 another white wire came off the ignition switch to the tach, through the pickup, and on to the coil +ve on another white.  So that is the next thing to trace through.  As a 66 the tach will have a third white wire to power its electronics, but that (and the accompanying earth) are not required to start the engine.
> 
> PaulH.
> 
> 
> ----- Original Message ----- 
>> My project car, another 1966 MGB, is fully assembled. Today I was trying to fire it up for the first time. But I knew I had an problem when the fuel pump failed to start clicking when I switched on the key. First I started troubleshooting the fuel pump,, but it soon became apparent that there was a general lack of juice roughly everywhere downstream of the starter. The alternator light came on, the starter cranked, but no lights and no accessories. Unfortunately, it is a little more difficult to figure this out than it should be, for several reasons:
> 



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