[Mgs] Soliciting advice on an electrical problem

Max Heim mvheim at sonic.net
Sun Jul 22 23:37:17 MDT 2018


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:

1. Car is converted to negative ground, in theory. To explain that, we need to look at he process that got me here...

2. This car (let’s call it “B”) was a semi-disassembled rolling shell. So the suspension and drivetrain, and many other components were transferred over from car “A” (my driver since 1988). So car B is not only using many of the same parts, it is mostly set up the same way. Mostly...

3. Some items that seemed to look OK were kept from car B. This included the wiring harness, which didn’t seem as hacked up, and most of the dash switches, and the tachometer and speedometer. So you might see where this gets sticky....

4. Without getting into details, we can’t assume everything is strictly according to the wiring diagram. Although in this build, I really tried not to make any more alterations than necessary to accommodate the 3-wire Bosch alternator and optical trigger ignition (both of which were working in car A). I can describe specific details if required.

I ran out of daylight today, but I will be reexamining the situation. I just wondered if anyone had some obvious places to start checking. One item that occurs to me is the tach — I was assuming it had been converted for negative ground because the battery cables had been switched, and when I looked inside it, it looked like some non-factory soldering had been done. I’m just not sure what the electrical fallout would be if it wasn’t — I would have guessed it just wouldn’t have registered. But a lot of white wires go through it.

Max
1966 B
Sent from my iPad


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