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MG MGB Technical - low beams go out

When I use the turn signals the low beam headlights go out. If I switch to high beams they come on. If I then switch back to low beams they will come back on, Only to go out again if I use the turn indicators. The turn switch is fairly new. The headlights have been upgraded to Halogen several years ago. Have I damaged the switch? Does the hazard switch have any impact? Sure gives a person a thrill trying to drive at night!
bs stone

The switch has spring leaf contacts which provide switching between main (high beam) and dipped (low beam). That circuit directs power to either main or dipped, but not both. The momentary flash feature will flash the headlights on main whether they are on or off, and if on will send power to main AND dipped, which is a lot of current through the switch (hence the word 'momentary'.

You can take apart the switch, clean the contacts, disassemble the leafs by drilling out a rivet and replacing with a small screw and nut, and generally rework the switch.

You may need to study your wiring diagram, and also test the switch with a multimeter to fully understand the way it works, but unless you have severely melted plastic parts from too much heat, I bet you can repair it.

warmly,
dave
Dave Braun

Turn signal (multi-function switch on some makes) is a common point of failure on many makes of vehicles for what you have described.
Sometimes the switch can be disassembled, the contacts cleaned, lubed, and reformed.
If you are concerned about the electrical load of the headlights going through the switch, install relays. A wiring diagram for installing relays is available at http://www.advanceautowire.com look at the instruction manual for the headlight relay kit.
Kimberly

Can't speak for all years but for many middle years the contacts are exposed and the switch doesn't need dismantling to clean them. I doubt they need cleaning anyway, the switch being fairly new, and the problem being that the dipped beams work, but go out when the turn signals are selected, it just sounds like a faulty switch to me. If 'fairly new' is close enough to take it back to the supplier then I'd do so, it's only by rejecting poor stuff suppliers will get to know about it and hopefully do something about it. If it is too old for that then you might be able to glean some useful info and tweak the contacts so they work as they should by having a look at http://www.mgb-stuff.org.uk/wn_electricsframe.htm clicking on 'Lighting', and scrolling down to 'Dip Switch'.
Paul Hunt

This thread was discussed on 27/09/2008

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