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MG MGB Technical - Elec Help Turn Signals

Can anyone help with a problem I am having with my turn signals on my '79 B. I finall got them working but they flash slowly and the tach needle drops about 500RMP with each flash. I know that this is an electrical problem, possible a faulty ground? thanks for any help.
Scot Macdonald

Start by going through all the wiring from the trunk to under the car, to the column. Check all the connections - take each one apart, clean them, and see where you stand. You can turn on the lights and test each joint with a test light. As with any electrical problem, a test meter is the only tool that will clearly tell you the problem. Anything else is just speculation.

Jeff Schlemmer

Scot, I had the same situation.

It was corrected by cleaning the alternator connection, the starter wiring connection and installing a new battery ground to the chassis.

I don't know which of these items corrected the problem... they probably all contributed.... but the lights and starter had far more power than before.
Brian Denis

The tach and turn signals share the same green circuit for their 12v supply i.e. fused ignition. A common point for problems in this circuit is the fusebox i.e. spade conenctions, fuse holder and the hidden rivetted connection on the back. However there are also two 4-way bullet connectors behind the dash that are also common to both those circuits, plus a dash harness to main harness multi-way connector. If the brake lights affect it in much the same way then it must be the fusebox or earlier because of how the wiring branches off to each circuit. But if not then one of the aforementioned bullet connectors or dash connector is indicated. It must be a really bad connection to affect the tach that much, for battery or starter connections to be the cause you would have other problems like slow or non-cranking. But if a car has one bad connection due to the passage of time then it is quite likely to have others, and possibly more than one affecting the same circuit. A voltmeter used on the green points mentioned and others like the white/brown at the fusebox, brown at the ignition relay and starter solenoid for example, will indicate which two points the problem lies between.
Paul Hunt

I had a similar problem. Addressed the connections aspect and removed front and rear light units, tidied all grounds etc, replaced faulty or suspect connections, checked flasher unit and connections and found the problem persisted. Then the batteries went flat. Turned out the cause of that was a faulty regulator. Replaced that and, bingo, the flashes were working. Not sure of the hows or whys, but happy with the result.
Roger Taylor

This thread was discussed between 11/11/2004 and 13/11/2004

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