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MG MGB Technical - Indicators causing chaos again!

I have a 1978 mgb roadster. Very often when the indicators are switched on (either side) they don't work, the tachometer drops and heater doesn't work. This problem will right itself eventually when the tach picks up - until the next time.
When the indicators aren't working I've checked the green wires both sides of the hazard switch and there is no power to either side, although theres power going from the green wire from the fuse box (2nd fuse up). Theres also power either side of the green wired 2x 4 point bullet connectors under the right hand side of the dash. Am I right in assuming that the bad connection must therefore be between the bullet connectors and the hazard switch? If so other than the multi connectors behind the left hand side of the dash (which look ok) what should I being looking for?

This problem is sending me bonkers, preventing me from driving my car and any help would be much appreciated. Thanks.
D Callaghan

I can"t be sure this is the cause but have you checked behind the fuse box. They have a habit of corroding and going high resistance between the rivet and connecting blade.
jim soutar

Whilst the fusebox is a common cause of this problem, if you definitely had 12v on some green wires when you didn't at the greens on *both* sides of the hazard switch, it isn't the problem in this case, neither is it the other common case - the hazard switch itself.

On a UK 78 the routing is quite convoluted as it goes in and out of the dashboard multi-way plugs, which probably aren't accessible unless you pull the dash forwards. The supply comes through one of these plugs to one side of the hazard switch and from there is daisy-chained to the heater switch and the tach, which because that drops as well does indicate it is the supply to the hazard switch that is at fault and not the switch itself or anything after it. The supply to the multi-way plug comes from a 4-way bullet connector. That feeds the wipers, fuel and temp gauges and handbrake warning circuits so if those continue to work it can only be the one wire coming out of the bullet connector going to the multi-way plug, or the multi-way plug connection itself. The feed to that bullet connector comes directly off the fusebox, so only if all the circuits I've mentioned are affected could it be that spade at the fusebox or the bullet going into the 4-way connector. Another green comes off the fusebox feeding the washers, brake and reversing lights so only if those are failing as well would it be the fuse, it's holder or one of the rivetted connections on the back. Lets hope it is the bullet connector, of which there are several behind the dash, so you have still got some work to do.
Paul Hunt

This thread was discussed between 09/11/2009 and 10/11/2009

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