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MG MGA - Another Lucas Mystery

I haven't had an electrical problem in over 12 yrs since rebuilding the 1500, but a new one arose today. The car is dead though there's power to the starter switch, voltage regulator, ignition switch, and fuse block (anything fed by the big brown wire coming off the starter switch) WHILE THE KEY IS OFF. When I switch the key ON, all power to the above listed items is lost. One more thing, when I pull the cable of the starter switch, there's no power to the starter side of the switch (so the starter doesn't turn).
I would appreciate any clues.
thanks,
Tyler
Tyler

Hi Tyler. I'm not an electrical expert by any stretch, but it sounds like at least part of the problem is the ignition switch. You state that power is delivered to several components when the switch is off, and yet power to these items is lost when the switch is turned on. To me, this sounds like a defective ignition switch. Perhaps you should pull the wires going to the ignition switch, and twist them together, on a temporary basis. If the components that were formerly dead with the ignition switch turned on, now "come back on line", then the ignition switch would seem to be toasted and needs to be replaced. As for the dead starter motor, that is curious. The starter circuit is completely separate from the wiring harness, except for a brown power feed wire coming off one terminal of the starter switch. Since your starter does not work, the most probable causes are: dead or weak battery, dirty or loose battery terminals, dirty or loose starter switch terminals, bad ground connection to the frame from the battery, bad starter motor, or bad starter switch. I would check all these items carefully, cause one of them is likely causing the no spin starter problem. To save time, you can first "boost" the battery in your car. Use a known good battery, and simply hook up the booster battery to your car's battery. Positive to positive and negative to negative. Try the starter pull. If the engine cranks, you likely have a dirty connection/bad cable issue. If the stater doesnt crank, then secondly, take the jumper cables and connect a known good battery to the starter motor. If your car is positive ground, connect the red cable to a clean ground. Connect the black cable to the starter motor cable (attach it at the starter switch) If the starter then spins, you can eliminate the starter as the problem, and concentrate on the other issues noted previously. Hope this points you in the right direction. Cheers! Glenn
Glenn

Hi Tyler. Someting else to check is the ground strap going from the motor mount to the frame. If the connections here are not clean and tight, the starter wont spin either. Cheers! GLenn
Glenn

You have a bad connection between the battery and the switch in either direction. Most likley dirty battery cables next likley bad ground strap then poor cannection at brown wire to batt cable at starter switch.
When somthing looses power when something else is turned on you have a voltage drop.
Check the simple first. Bad connection. Not Lucas just old.
Good luck Randy
R J Brown

If the battery is charged You have a bad connection between the battery and the switch in either direction. Most likley dirty battery cables next likley bad ground strap then poor cannection at brown wire to batt cable at starter switch.
When somthing looses power when something else is turned on you have a voltage drop.
Check the simple first. Bad connection. Not Lucas, just old.
Good luck Randy
R J Brown

Thanks Randy,
That was it. Although it did not look dirty, I cleaned the battery posts and clamps, and now it works fine.
thanks,
Tyler
tyler

I learned that the hard way working in a gas station 30 years ago. I was told to replace a starter and when the third one didn't work I cleaned the battery and it started. Glad I could help, Randy
R J Brown

This thread was discussed between 20/08/2005 and 24/08/2005

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