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MG MGB Technical - MG dies w/o warning

Hello, I purchased a 76 MGB about 3 weeks ago and drove it home 200 miles with no problem. The problem started when I turned on the headlights about 2 weeks ago and the used the turn signal. The turn signal stopped working as well as the gas gauge and tach. The turn signal switch shorted and needs replaced. The next day when I went to start it, it wouldn't start. It would turn over but there was no spark in the wires to the plugs. After messing with the wires it ended up starting, but now when I am driving, it shuts off w/o warning. I pull over, wait a few minutes and then it restarts w/o any problems. The problem is on-going. Any ideas?
Frank

Does your distributor have points or is it the original electronic distributor? Do you have any electrical test equipment, meter or test light? Why do you say the turn signal is shorted? Shorted circuits normally blow fuses or make smoke. Which wires were you messing with when it started? Suppling more information will help.

Clifton
Clifton Gordon

A common problem on lots of LBCs is the Lucas fuse block. The fuse holding contacts are riveted through the plastic base to the spade connectors on the bottom. All too often these rivets loosen a bit and cause intermittant connections, usually noticed by several systems failing at the same time. I have repaired several by using a soldering gun or large iron and plenty of flux and soldering the spade connectons to the rivets on the bottom side. I don't have the B wiring diagram here with me, but I think the systems you notice going out will be common to one fuse on the block.
Bill Young

With a car new to you there could be any number of things wrong with the car, including dodgy electrics due to lack of care and poor maintenance. Sounds like at least two problems here, possibly three.

The headlights come directly off the brown i.e. no fuse. The problem with those could be the main lighting switch or the dip-switch.

If the car cranked then voltage was reaching the switch ignition itself, so any lack of sparks will be down to the white circuit or the ignition components i.e. the distributor and coil.

The turn signal, gas gauge and tach all come off the green fuse, it's not unknown for this to go high-resistance either internally or at the connections. This is fed from the white circuit so there could be a common cause for the lack of sparks, turn signals, gas gauge etc. But if the engine continued to run when the turn signals etc. failed, and the sparks only failed subsequently, then you are probably have at least three faults. And given three the whole electrical system is probably in a mess.

You will have to pick one fault and work through that logically with a voltmeter, don't expect to find a 'magic bullet' that fixes all of them.
Paul Hunt 2

HI Frank,

As I have found out even with a new wiring harness You can still have shorts. Lucas wiring seem to have a common problem when a live wire rubs a part of metal on a British car the fuse does not always blow. The wire will just rub and then burn and then You have a problem.


The very first thing is look for any poor wiring connections that the P.O. might have rigged. This is common for a novice car mechanic or just trying to save a almost dead Lucas harness. The short that you have might be in the green wire witch powers the Fuel Gauge, turn signals, brake lights, revere lights, and transfers Power to the fuel pump and tachometer wires which should be white.


I know this is a lot for a poor Lucas fuse box to handle. I sometimes wish the would have mad a fuse box that would only have on or two circuits going to them. I hope this helps....

James
James

Thanks for all the help, I will start with getting the turn signal switch replaced. When I bought it I knew the turn signal was sketchy as it didn't click into place. I did notice that it blew the third fuse down on the box. When I put a new fuse in and started the engine it blew it right away. I will then move on to the other possible troubleshooting ideas provided. Thanks for the suuport. Frank
FJE Frank

Frank - part of your checklist (hinted at in Paul's post) should include the white wire circuit. On both my cars (earlier than yours, but probably similar) there's a connection visible near the fuses where there are two white wires connected to one white wire. There is a double slotted aluminum sleeve inside the wide rubber sleeve. That sleeve can corrode invisibly, causing intermittant failures before the connections are permanently severed or turn to aluminum oxide dust. Not so dire, the sleeve may just loosen over time, leading to intermittant failures, too. Still that's a matter of fatigue and getting a spare sleeve is cheap insurance.

"It's happened to me".
John Z

I had (have) similar problems on my car. Try cleaning the terminals at the ignition relay. Mine is mounted on the passenger-side fender of the engine bay. If the wires are not making good contact with the relay you will have the exact symptoms you describe.
Randy
1977 MGB
randy olson

This thread was discussed between 17/08/2007 and 24/08/2007

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