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MG MGB Technical - Smoked!

Mr. Lucas has struck again!

I first noticed strange problems a few days ago driving my 77B. The electrical system appeared to "blink" off for a second or two - usually when under load like driving up a hill. It happened two or three times, but never long enough to kill the fuel pump and stop the car.

Today... ouch! The system went "poof" while driving home and the wiring under the driver side smoked away. (Mostly melting insulation it appears.) After letting her rest a few minutes (and after cleaning the poop out of my seat) when I turn the key I get juice - the instruments, lights, and radio work, and she'll turn over just fine, but won't start.

Here's the questions: 1) What's the most likely cause? 2) Am I going to need to replace the whole wiring harness, or just the dash sub-harness, and 3) what else do I need to plan on replacing - alternator? coil? battery and cables?

Par for the course - she's DOA right about the time we're getting the picture-postcard spring weather when I want to drive her the most!
Scott K

Scott-
You've obviously had a big-time short circuit, so it'll be impossible to say what damage has been done until the system is rewired and the individual components can be tested. Since your wiring loom is ancient, 95% of your electrical problems probably stem from it. Want reliability? Trash all of the old loom and replace it with a top-quality loom from British Wiring. They have a website at http://www.britishwiring.com/
Steve S.

If turning off the ignition stopped the smoke then the short was in the white circuit. That could be the fuel pump, overdrive (if it was engaged at the time) or anywhere else. If the fuel pump or OD their respective looms will have been damaged as well as the main loom, if 'anywhere else' probably only the main loom. Finding which wires have been damaged (by carrying too much current (not simply from being adjacent to a wire that was) and seeing what it feeds should lead you to the original problem - which you really need to found before you fit a new loom! Checking the ignition circuit through seems like a good place to start. The dash loom is unlikely to have been affected. Alternator, battery, coil are unlikely to have been affected (the coil could just have been the cause) but the ignition switch may now be high-resistance.
Paul Hunt

This thread was discussed on 24/05/2002

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