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MG TD TF 1500 - Front fog lamp, TD

After many yeas I just noticed that my single front Lucas fog lamp that is wired into the factory harness only works with when the side lights are on, not when the headlamps are on. Is this the way they are supposed to operate?
John Quilter (TD8986)

John, you've got some odd wiring. The side lights should be on when the headlights are on, so it's correct for the fog lamp to be on when the side lights are on. Don't your side lights come on with your headlights? Any chance that you have relays in your headlight wiring? Bud



Bud Krueger

A clarification: position one on the lighting switch, side lights on and fog light enabled through smaller finger switch on the right. Position two, headlamp and side lights on but fog light does not operate in this position. I'm guessing this is normal but prevents the fog light being used as an auxiliary driving light.
John Quilter (TD8986)

John: Can you post a picture of your switches you describe? I am having a hard time visualizing the smaller switch.
Christopher Couper

Chris, it's the OEM switch between the choke and the dimmer switch. I think John just sees it as an odd shaped switch, it's not round, it's rectangular. Bud
Bud Krueger

Here is a pic of the dash. One switch is visible the other identical looking one is behind the key fob. The left one is an on off switch for the instrument lights the right one controls the fog lamp.


John Quilter (TD8986)

John, as created the gadget behind the keyfob should be a round knob rheostat that varies the dashlamp brightness. The rectangular knob one is 'supposed' to be the fog lamp switch. Bud
Bud Krueger

Perhaps the wiring is such that the fog/driving lights come on only when the main switch is set for side lights or main beam on low beam but are blocked out when the main lights are on high beam. I've seen other systems like this. I might tomorrow be able to see if this is the case with my '53 with the foot operated dimmer switch.

Jud
J K Chapin

According to the wiring diagram it should be powered whenever the side lamps are lit.

So it can be on when the headlamps are off or on.




Christopher Couper

Well after double checking tonight it all works as intended but the main headlamp switch is a bit wonky and sometimes takes a bit of jiggling to get to make proper contact.
The instrument light switch, however, is just an on/off type, not a rheostat on this mid 1951 TD.
John Quilter (TD8986)

John: That is a replacement headlamp switch which is pretty normal nowadays. The little window gives it away. It may need a bit of cleaning but they are usually pretty stable. You could just disconnect your battery and cycle it about 50 times to clean it.

So you don't have a round rheostat like dash dimmer hiding behind your key fob?

The switch for the fog lamp that is touching your fog lamp is just on/off but IIRC can be rotated through 360*.
Christopher Couper

This thread was discussed between 03/06/2021 and 04/06/2021

MG TD TF 1500 index

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