Horn wiring diagrams

[Andyh]

I have a 1968 MGB GT with a single horn with two connections (P and PB) where the horn push on the steering wheel is earthed. (pre-1977 system)

I have inherited two new horns with one connection as these are the type fitted to cars from 1977, where the horn is earthed. (Post 1977 system)

Can I fit these horns to a pre-1977 car...and if so can someone please give me a simple/clear wiring diagram...including the installation of a relay.

I do have Rick Astley's excellent book "MGB Electrical Systems" and this gives both the pre and post 1977 wiring diagrams...but not whether or how to wire a pre-1977 car with post 1977 horns!!

Your assistance is appreciated

[Charles Farran]

Hi Andy,
I think this should work - using a relay seems to make the task easier as you don't have to isolate the horn bodies from the chassis which would create problems...
Have a look at my poorly drafted diagram. At your own risk of course if followed - others may have observations.
You will need to ensure that the relay is earthed via the horn push circuit & not directly earthed to the chassis.
On my diagram i haven't made it clear that the opposite side of the horn push goes via the B wire to earth.
I have included an additional line fuse as a safety precaution.
Apologies that the scan is side ways on for some reason!
Cheers
Charles