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MG MGA - A little wiring question

Hey fellas,

So I wired the dash harness and the main harness from the firewall today and I have two questions.

1) I have two red wires on the dash harness that I'm not sure where they go, see attached image. The one on the firewall harness goes to the lighting switch as do the other two on the dash harness. This is per my wiring diagram and old harness. However, these slightly large red wires are only in the dash harness and I'm not sure where they go. The only think I can think of is they are the jumper from the main light switch to the fog lamp switch. Can anyone tell me what these are for? Am I right in they are for the fog lamp switch?

2) My new harness did not have a ground for the horn. I made a simple jumper that I will ground at the same point as the other three wires one the back on the water/oil gauge but can someone confirm this is missing in the harness? My original harness had a wire running from the horn to a connector with two other ground wires making three total that grounded to the water/oil gauge. I've wired my new harness the same way and just used a spare bit of black wire from the original harness, but I thought it odd that my wiring diagram and the old harness both have a ground for the horn push button and yet the new harness doesn't have this, but it does have the power for the horn.


Christopher Wilson

1) Light Switch (S1) has a jumper to Fog Light & (S1)a jumper over to Panel light Rheostat & the mailn red wire on S1 goes th the front & rear running lights. You should have 3 red wires on (S1).
2) staring with the wiper switch to the fuel gauge from FG to horn & panel light from PL to mail body ground & SpeedO on to Tack
This applacation is what I used on my 57 1500
Hope it helps:Cliff(SC)


Thanks for the input. My S1 indicates 4 wires.

If you look at the photo you can make out S1 in the background. It has three reds already, though no jumper to the fog light.

The ones I have are

1) Main harness to switch (S1)
2) Rheostat to switch (S1)
3) Map light to switch (S1)

and the two shown but as yet unidentified larger red wires on the dash harness only. The reason I know they are not the Rheostat or map light wires is they are a slightly larger gauge.

Christopher Wilson

This thread was discussed on 19/04/2009

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