It is very important to note that the 1969 TR6 (and TR250) horns do not use a relay. Instead there is a permanent positive feed to the horns on a purple wire and the purple/black wire goes back to the horn push where it is grounded when pressed. In 1970, this was changed to relay operation, presumably to cut the current being carried by the horn push. Note that there's a current-limiting resistor in the horn push circuitry, and, as I found out, this is insufficient to drive two later horns, as they draw too much current and the voltage drop is insufficient to make them operate. Also, on the later TR6s that purple/yellow wire is not always charged, despite what is said at 0:36. It's a switched +12v, and only the '69 TR6 and TR250 has a permanent live. The simple solution to this is to install a relay near the left hand front horn where the purple permanent live and switched neutral appear. The cables have to be cut and then wired to operate the relay coil with the permanent live (purple) also connected to the one of the relay contacts. The second relay contact is then connected to the purple wire to the left hand horn, making it a switched live and then purple/black wire interconnecting the two horns must then be grounded. Note that there are relays available which incorporate a fuse, and it's a good idea to use one of those to provide a bit of extra protection as it will avoid blowing the fuse in the fuse box if there is a short provided, that is, the horn fuse is lower rated. Of course, what is better is to redo the fusing anyway. There are only 4 fuses in a TR6, and far too many circuits share the same fuse, and the ignition switch circuit carries the current for any devices that are only active with the switch turned on. Much better to have a fuse box with modern blade fuses and a relay to reduce the load on the ignition switch. Then split off circuits so they aren't all concentrated on a few fuses. That said, if it was all to be done according to modern standards, then that would essentially mean redesigning the loom, but it's possible to make improvements with minimal changes without doing things like switching the headlamps via relays.
Well said and absolutely right. Each year has a different set up slightly but people change things so we can only fix what is in front of us. All very good information. 👍
Excellent series - just subscribed. Maybe worth pointing out that replacement steering racks don't have the top service bolt, so there is no way of reliably earthing the horn push button. My '6 has an aftermarket rack and worked intermittently, presumably depending on accidental earthing elsewhere along the column. Solved by putting a 32mm dia jubilee clip around the top of the rack gearcase (which was scraped to get a good connection) and attaching an earth lead to it.
Excellent information as not every car is the same regardless of the bad of old wiring. We can only fix what is in front of us but any help goes a long way. Much appreciated 👍
Hey there. Thank you for the video. I have a (very rookie) question. On the relay, if I have everything but the PB wire hooked up, and then ground that PB terminal on the relay to neg on the battery, should I hear the relay click and see 12v on the PY wire terminal? With everything hooked up if I pull the PB wire and ground it to the neg terminal on the battery I get nothing. I think may issue is that I have the passenger side horn off at the moment (on a US car). Looks like I'll have to pull the shroud, but if you happen to see this, do you know which horn is connected first to the PY wire? I assume the other horn jumps off that one
