[Mgs] Was: coil; now wiring issues

Tue Jul 31 02:02:35 MDT 2018

Ah, this is the tell-tales that are the wrong way round?  Looking at the diagram your switch does indeed seem to be incorrect, but surely the simplest way to deal with that is swap over the light-green/blue and light-green/yellow wires where the switch connects to the main harness?  Unless both tell-tales come out of the harness together it shouldn't be possible to get them reversed on the dash.  

The switch is designed this way because MG decided to use separate tell-tales for left and right, and the flasher units at the time needed a third terminal to flash the tell-tales, so that third wire has to be switched as well.  Triumph used a single tell-tale, so the third terminal was simply wired to the light.  Later on when the flasher units were designed to flash both the corners of the car and the tell-tales from one output terminal, the tell-tales were simply wired in parallel with the main lights.

But I don't understand why the flasher unit ticks when neither of the main bulbs light on the green/white side. The only way it can do that is if there is some path to earth when the switch is operated to that side.  Either it is connected to some other circuit on the car, or the switch is faulty.  Disconnect the green/white wire and see if it still ticks.  If it doesn't then there is some problem in the green/white circuit out to the lamps.  As a test swap over the green/white and green/red wires and see which side works then.  As another check if you connect 12v to the green/white do the corners of the car light then?

If it still ticks with the green/white disconnected then disconnect the light-green/brown wire and see if it ticks then.  If it doesn't then there is a fault inside the switch.  I can't see any possibility for the flasher unit still ticking with the light-green/brown wire disconnected.

As one pair of wires may be incorrect, then maybe there are other incorrect colours as well, and you will have to check the continuity of all the circuits.

Black should be connected to light-green/yellow when switched to the left, and to light-green/blue when switch to the right, but these are already suspect.

Light-green/brown should be connected to green/red when switch to the left and green/white when switched to the right.

If you have a headlamp flasher then brown is connected to blue/white.

As well as checking each wire is connected to wherever it is supposed to be connected to, you have to check it isn't connected to anything else, and that includes when the switch isn't operated.  So you have to test each wire against every other wire, with the switch not operated, then operated to the left, then operated to the right.  Make a chart of which wire shows continuity to which other wire or wires, you will never remember.  Maybe one of the tell-tale wires has been reversed with one of the main wires.

PaulH.
  ----- Original Message ----- 
  From: Max Heim via Mgs 
  To: mgs at autox.team.net List 
  Sent: Monday, July 30, 2018 5:31 PM
  Subject: Re: [Mgs] Was: coil; now wiring issues

  The wiring diagram shows an LG/U wire from the switch to the RH indicator, and LG/Y to the LH indicator. When connected this way, the RH indicator flashes when the switch is left, and vice versa. Looking at the naked switch, these wires are clearly originating on the “wrong side” — the LG/Y is on the same side of the unit as the G/W which leads to the RH lamps, so it can’t possibly operate the LH indicator, and so forth.

  But I can’t determine if the mistake is in the part or in the labels in the diagram, since all one has to do is unplug the lamp and move it to the opposite socket in order to make the colors match up. This part is at least 15 years old so it is not eligible for returns. I don't know why I didn’t notice the discrepancy when I installed it in the old car. Possibly I assumed I had the lamps installed incorrectly and just swapped them without checking colors.

  The flasher works — when the switch is left the indicator and both lamps function correctly. When the switch is right, the indicator flashes but the lamps do not. Bulbs are confirmed good. Presumably the grounds at the lamp units are good because the taillights and running lights work.

  I was saying it had to be a fault in the switch because I can’t find any voltage anywhere on the G/W wire, not even where it exits the switch — on the back side of the rivet that is the contact point. This is despite the fact that it is located adjacent to the contact for the LG/Y to the indicator, which works, and is supposed to be switched simultaneously. I have been checking this with a test lamp as my digital multimeter will not show any reading on the flasher circuit.

  It occurs to me that if I jumpered the two contacts with some solder on the wire-exit side, they would “have” to function simultaneously. This could be a possible solution. I can’t think of any reason why they would need to be independent (but then, why were they built that way in the first place?).

  --
  Max Heim
  '66 MGB
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