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MG MGA - Dash Wire Harness Question


Almost finished wiring the car. It looks like I have a couple left over on the dash harness.

I have two brown with black (two ends, one wire). The diagram does not show this color in the dash harness. There is brown with black for the horn but that is part of the main harness. There is nowhere obvious to put it - everything is wired in. Just seems like an extra wire. Any ideas?

The harness was purchased from British Wiring.

Help appreciated.

thanks
Jeff Bennett

Jeff,

The Series MGA Workshop Manual shows:

Brown with Green (NG) from the fuse (A2) to the horn(s) and Brown with Black (NB) from the horn(s) to the horn push button on the dash. It shows the other end of the horn button to ground.

If twin horns are fitted, there is a Brown with Black (NB) jumper to each horn from a connector block on the Blown with Black (NB)wire that runs to the horn push button.

Steve
Steve K

Steve,

One of these days I'm going to crack open that manual!

So I think what your saying is that the extra wire is there if I had dual horns. Since I do not, I can just leave it unconnected.

Thanks


Jeff Bennett

Jeff,

Given the color, I'd say it was intended to be associated with the horn(s). However, as I recall, the split for twin horns occurs close to the front grill, and not behind the dash.

For now I would just leave it disconnected and cap/tape both ends to be sure they can't come into contact with metal, especially ground.

When I have a chance, I'll follow the wiring for the horn on my MkII and see if I can determine how the Brown with Black makes its way from the horn to the push button. Perhaps someone else already has their car uncovered and can already comment.

Steve
Steve K

Brown with black stripe is the horn grounding connector between the main harness and the dash harness, going to thr horn push button. It requires an in-line snap connector to join two bullets ends. This snap connector is the only connection directly between the dash harness and the main harness. All other wire ends behind the dash connect from one of the harness sections to a dash device.

The short browN/Black wire in the dash harness has a small ring connector on the other end that attaches inside the horn push button. See here: http://mgaguru.com/mgtech/electric/circ_fd.htm
and hereL http://mgaguru.com/mgtech/electric/et100b.htm
Barney Gaylord


So the brown with black from the dash harness is connected directly to the horn button. The other end is connected to the main harness.

Interesting to note that the fancy laminated color wiring diagram I purchased for $20 missed that one.

thanks
Jeff Bennett

I wondered for a long time why the browN/Black wire in the main harness was not connected directly to the horn button. This is a single exception to on otherwise simple wiring tradition, and it makes necessary the addition of an extra wire in the dash harness and the odd snap connector. My conclusion is that it was done to accommodate the "old" design of the horn button that requires the button to be partially disassembled to connect a wire inside. In production they would want to connect these wires inside the horn button during bench assembly of the dash, before the dash assembly was "offered up" to be connected to the main harness in the car. Just a guess really.
Barney Gaylord

What if you did go direct, skipping the wire in the dash harness?
Jeff Bennett

No problem functionally. It would work without the snap connector, and leaving the NB wire in the dash harness disconnected. You would need to cut the bullet off the NB wire in the main harness and install a small ring lug. Thereafter any time you wanted to connect or disconnect the dash from the car you would have to disassemble the horn button to service that one wire.
Barney Gaylord

This is a subtle point, but when the wiring harness is installed according to spec, the Brown with Black (NB) wire - like the Brown with Green wire - is hot and can deliver significant current (limited only by the fuse) through the relatively low resistance horn. The only time the NB wire is close to ground potential is when the horn button is being pushed. (That may be why it's colored Brown with Black, and not Black with Brown.)

Hence, when working on the wiring be sure the battery is disconnected, and be sure free wire ends are covered with insulation. The last thing you need is an unexpected spark under the hood (bonnet).
Steve K

Brown is always hot. Black is always ground. Anything with a stripe is switched or regulated. Ergo, black with a stripe or any other color with a black stripe is switched to ground. Brown with a stripe is a switched or regulated always hot wire.
Barney Gaylord

Barney - how about my Lucas fog light? Two wires coming from the light. One is red the other is brown. I would think the brown is the ground.
Jeff Bennett

Jeff B
The wire to the fog light from the switch is red with yellow stripe. The R/Y is the only wire in that circuit the light came with the ground wire. The red and brown wires coming out of your fog light are part of the light. They are not part of the car's wiring harness. Red is the main color of the lights powered by the first stop on th headlight switch. Red goes to fog light switch and red yellow is the switched wire from the fog light switch. As Barney explained.
R J Brown

This thread was discussed between 26/04/2008 and 30/04/2008

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