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TR2/3/3A Tr3a - no horn

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angelfj1

angelfj1

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The horn in my 3A stopped working recently. I checked all of the obvious things. The horns do sound when connected by jumper to the battery. The fuse is OK. The wiring to the horns is OK as there is a constant 12V at the horns. I isolated the NB wire coming from the steering column harness and connected my digital multi-meter to it (on the ohm scale) and to earth and then pushed the horn button. The meter reads inf. or open circuit. I have heard of situations where the horn circuit would short out and the horn would sound during a turn or with heavy torque on the wheel. However, I was not aware that they could fail as an open circuit. This car has clocked a few thousand miles since a complete restoration in 2012 and has been garaged ever since. The control head was new from TRF when installed. This car has an adjustable steering wheel. In order to further diagnose this problem does the control head have to be removed?

Thanks, Frank
 
Hi Frank. It kinda sounds like a broken wire to me inside the control head. Cheers, Mike
 
The control head will definitely have to come loose for further testing. However, you don't necessarily have to pull the harness completely out of the stator tube. Loosen the 3 grub screws in the back of the steering wheel and provide a little slack at the steering box, then you can pull the head out far enough to remove the 3 flat head screws through the holes in the plate. That will let you pull the head away from the plate assembly, and test directly on the wire terminals. If it is a broken wire (or the brass ground strap inside the head), then you'll also very likely see the damage at that point.

This photo is off the car obviously, but I have done it on the car. The screws laying on the table are the 3 screws I'm talking about. No need to remove the 3 larger round head screws at this point.


Here's a shot showing what you'll see after separating the plate from the head. I had already removed the 3 round head screws for this shot, but you can still leave them alone.
[URL=https://s258.photobucket.com/user/TR3driver/media/Control%20Head/DSCF0006_crop1.jpg.html]
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