TR2/3/3A TR3A Horn Issue

[BritCars54]

After several days of trying to troubleshoot the horns on my 60 TR3A, I fortunately had to return to work today, giving me a week before I can approach the problem again, also allowing time for the Lucas-induced fugue state to fade. I have tested both horns (brief direct connect to the battery) and they appear to have the ability to function. I found all the appropriate wires on the wiring diagram.
The fuse is intact. With a testing light, the horn switch appears to work. I cleaned up all connections. I have the Green Brown to each horn, Brown Black to passenger horn, which combines with another Brown Black that crosses over to the driver side. This then combines with the Brown Black from the horn switch that comes out of the bottom of the steering column, and these connect to the driver's side horn. No response. I did also found a Brown Black wire coming out of the drivers side harness, but the wiring diagram does not show such a wire.
Any suggestions?
Thank you.

 

[TR3driver]

There's something wrong with that description. The 3-way connection should be on the driver's side, between a NB wire to the horn, a NB wire to the control head, and a NB wire from the harness. On the passenger side, should be only a NB from the harness joining the NB from the horn. Sounds like someone has added a second NB wire that crosses from side to side.

The horns draw a lot of current and are pretty picky about voltage, so connections that appear to be good by ordinary means may not be good enough. I've also had problems with bullet sleeves that were broken inside and so didn't make good connection even after cleaning. Probably a good first step is to just replace all the sleeves in the circuit to/from the horns.

If you can, get someone to hold the horn button down while you use a test lamp (with a sharp probe) to probe the wires right at one of the horns. I'd start on the driver's side. You should find that the NG wire has 12v and the NB does not. Then follow the side that is wrong, back until you find the problem.

 

[BritCars54]

There have been other things discovered on this TR3 that were not as Triumph designed. Will check again with the test lamp. I changed out what appeared to be bad connectors, but may just change them all out when I get back to it next week.
Perhaps a foolish question...if the wiring is as you describe, with no connection from passenger to drivers side, how does the passenger side horn receive a signal from the control head?T
Thanks very much Randall.

 

[TR3driver]

The NB wire in the harness (should) run from side to side.

Here's a copy of an earlier wiring diagram, that I modified to show the LHD connections to the control head. Some of the other details won't be right for your car, but the horn circuit is the same.
https://docs.google.com/file/d/0B2H2NJt34Offc1R3Szh4WG1ybDA/edit?usp=sharing

 

[BritCars54]

The diagram I had showed a similar pattern, but the NB came out of the passenger side harness and connected to that horn and the crossover wire. I will plan to try connecting as this diagram indicates.
Another question...an NB exits from the control head, but also from both the passenger and driver side harnesses. Is that the crossover NB exiting from the passenger side harness?
As you said before, the crossover wire that I am seeing was probably a second wire added.
Appreciate the input.

 

[martx-5]

I don't know about you guys, but I find the wiring diagrams from Advance Auto Wire much easier to follow then the original.

https://www.advanceautowire.com/tr24a.pdf

 

[BritCars54]

That is the diagram I was using, but the horn circuit is also understandable on the one Randall posted.

 

[TR3driver]

Another question...an NB exits from the control head, but also from both the passenger and driver side harnesses. Is that the crossover NB exiting from the passenger side harness?

Yup, it just runs through the harness (inside the cabin) from one side to the other. The TR3 harness has no connections inside the harness, all wires just run from point A to point B. Having it (and all the other wires that just cross over) run through the cabin helps protect the wires and simplify removing the apron.

The AAW diagram may be easier to follow, but it is also wrong in several minor respects. For example, it shows the NB wire from the control head going to the same junction as the NB from the RH horn, which is correct only for right hand drive cars. Most of the folks on this forum have left hand drive cars.

 

[BritCars54]

Very helpful Randall. Anxious to give it another go next week.
Thanks again.

 

[Don Elliott]

As I understand it, the extra wire from one side to the other was designed for use in TRs which have right hand drive.

 

[TR3driver]

As I understand it, the extra wire from one side to the other was designed for use in TRs which have right hand drive.

There is always one extra wire, but it's from the turn signal circuits. For LHD cars, there is a GR wire that is unused; while RHD cars have a GN that is unused.

But those wires are too small to work well with the horns, I believe. The NG and NB wires are much thicker.

 

[BritCars54]

The wire in the harness from side to side makes sense, to connect the 2 horns, and is not dependent on the steering column side. It also makes sense that the union of control unit NB to the driver side's horn and NB crossover would be located on the right or left depending on right-hand or left hand drive.

 

[BritCars54]

Update. The "aftermarket" crossover NB now resides in the trash. Wired as per the diagram supplied By Randall. Revised all junctions. BEEP BEEP! Thanks for the input. On to a more straight forward replacement of the worn out choke cable...