MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Horn Push/Dimmer Switch

Some time ago I posted a question regarding the Horn Push/headlight Dimmer Switch for MGTD.

I had installed a new switch which I believed had come from Moss, and found that it created a "dead short" in the horn circuit. When the Horn button was pushed, the centre return spring would o'heat and literally melt.

I received a number of responses to that post, indicating others had experienced the same problem, and that Moss would replace it.

As it happens, the part had been purchased from LBC, and when I described the problem to Jeff Zorn, he said he had had no trouble with that part, but if I returned it to him he would have his friend Rick Astley look at it. I have always been a "fan" of Rick Astley, and have a copy of his book, which I refer to regularly.

The reply I got from Jeff Zorn was that I didn't know what I was doing, and that there was nothing wrong with the switch.

Even though I have paid the grand sum of $4.50 to "repair" the switch i returned, and about $20.00 in shipping costs, I still have not received an answer to my basic question: why is it that when the new switch is installed in the car's horn circuit (two wires) the switch o'heats and the horn will not work, and yet when an old MGB two position toggle switch is installed into the circuit (using the same two wires)the horn operates fine, and the toggle switch dose not o'heat.

Greater than my disappointment with LBC, is the desire to have an answer toi this question. It also begs the additional question of whether there is more than one supplier of this switch. I can't believe there is enough demand to warrant more than one, but I wonder.

Any advice, suggestion, or comment on this problem would be sincerely appreciated.
JR Ross

It most likley is a Moss switch in any event. They are the main supplier to most of the dealers.
Tom Maine (TD8105)

JR,

For the life of me, I can't remember if the current is supposed to go through the spring or not. As you probably know, the horn circuit is a very heavy amperage circuit. I once limped home two blocks in my TD (after my ignition switch wiring came loose) by placing a paper clip in the fuse terminal between the brown wires and the white wires. The paper clip burned quite an impression in my fingers when I blithly removed the clip to stop the engine. My point is that if the spring is designed to carry the current, the heavier the current, the more the spring will heat, and the more it heats the greater its resistance, and so on... until the spring fails.

I do know that on the original switch the outer diameter of the switch made the contact to the case to ground the outer contact. The spring sits on a brass plate that is isolated from the case by a phenolic spacer. So I surmise that the spring touches the underside of the horn button, which is fixed to the contact rim, and which, when pressed down passes the current from the screw terminal to the center contact, up the spring, and to the grounded case via the contact rim.

If this is the case, the spring should be copper brass and thick, or it won't be able to carry the load. Since you probably need to open the switch up to install the grub screws that fasten the dipping and horn wires, examine the switch to see if the spring is supposed to carry any current or not, and to see if it is heavy enough to carry an appreciable current. Post some pictures if you can.

I like to assemble my horn/dip switches with wires with bullet connectors so I don't have to open my switch up to reinstall it in the system. The horn switch pictures are mostly in my instrument panel section of my website, and not the electrical section...

warmly,
Dave
Dave Braun

Take a look at the switch and see where the wires are running. The one I recieved also did a dead short to the horn. I fixed it myself with by moving all the wires one pole (I believe it was clockwise). Or if you see that is the problem and you don't want to do it yourself , then tell the vendor what the problem is and tell him to send you one that is wired correctly. If it was like mine then I'd be demanding the extra money you spent, returned. If and this is the if... yours was wired like mine then it was defective out of the box. Mine came from Moss. I have a picture of it at home but I'm not there. Search the archives and you will find the picture with your original post.
LaVerne

Look at the wiring diagram for the horns/swtich/lights. Then use a VOM to verify the switch wires/terminals are correct or not, as well as proper orietation of the switch. If that seems fine, may be time to put an ammeter in the circuit to check current draw to make sure not excessive. I could see someone testing the switch, but not noticing the wire colors were wrong? George
George Butz

I just installed one on my car also. Same thing, dead short. Ours came from Moss. The spring melted just as described above! The wires are incorrect on the switch as delivered from Moss. The hot wire is going direct to the horn button, which is incorrect.
RK Rich

This thread was discussed between 07/01/2011 and 23/01/2011

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.