I’ve just bought a 1983 850T4 from a mate who is selling off most of his classic collection. It’s been started regularly but not ridden in 18 months.
All the basics have checked out good or working apart from the horn.
The switch gear is the original lego style and when the flasher is pressed, there’s an audible click from the 5 pin flasher relay located on the frame below the tank. No click when the yellow rocker switch is pressed the other way for the horn.
There’s no 12V across the brown and black leads to the horn when the horn switch is pressed. Battery is load tested good and fully charged.
Does anyone know if there is a separate relay for the horn on this model? I’ve downloaded an old 850T Haynes manual which suggests there was one mounted near the rear mudguard, at least on the older models.
There is no horn relay on this bike unless one has been added by a previous owner. The brown wire is the feed and comes from fuse F2 via the flash headlamp relay, The horn button earths the circuit so to test place a wire from the black wire on the back of the horn(s) to earth. If the horns work there is something wrong with the switch or the earth from the switch. If the horn still doesn’t work there is something wrong with the supply to the horn. Check all connectors, pull them apart and clean.
Here is Carl Allison’s wiring diagram click here beware sometimes Carl Allison gets the colours confused White (Bi) with Blue (Bl)
I haven’t finished drawing this model myself as no one has asked for it yet! See my own wiring diagrams click here
I have just had a quick look at Carl Allison’s diagram (he has produced a great amount of good work) that I linked above and there are some errors that I can see, as listed below, there maybe others but I have not been through every wire.
Red (R) / Blue (B) wires from the brake switches to the brake light are shown incorrectly as Red (R) / White (Bi)
Green (V) wire from the ignition switch to fuse F4 is shown incorrectly as violet (Vi)
Black (N) / White (Bi) wire from the horn button on the left hand switch to the 12 pin connector (pin 11) is shown incorrectly as Black (N)
Blue (B) / Black (N) wires to the lights on the left hand switch to the 12 pin connector (pin 2) are shown incorrectly as White (Bi) / Black (N), also the flash note is too high on the drawing against the light switch, the flash button has the same earth as the horn and uses a grey wire to the 12 pin connector (pin 10)
Red (R) / Yellow (G) wire from the fuel level switch to the dash via the 15 pin connector (pin 15) is shown incorrectly as Red (R) / Green (V)
Blue (B) / Black (N) wire from fuse F2 to the flasher unit is shown incorrectly as White (Bi) / Black (N)
Blue (B) / Black (N) wire from the oil pressure switch to the dash via the 15 pin connector (pin 8) is shown incorrectly as White (Bi) / Black (N).
As I said in my last post you need to be aware that there may be errors on these diagrams, when I draw my own wiring diagrams I refer to the factory information and translate the wiring colours correctly.
If you have any questions please do not hesitate to ask.
Thank you very much indeed for taking the trouble to provide this additional information. I hope to find time this afternoon to troubleshoot the horn problem further.
Should you feel inclined or find the time to produce a T4 wiring diagram I’ll be your first customer.