Reliving my hours under the bonnet soldering and tracing vicariously through your efforts. Most entertaining to me, anyway. What a sad sounding horn! Steve from USA
I strongly recommend having a fire extinguisher - just in case the Prince of Darkness strikes again. The cheap ones use soda powder - highly corrosive to paint and electrics and you never get it out completely. Plus, spray time is very limited. Therefore, I have an AFFF foam extinguisher in my car. AFFF is used in race-car fire suppression, too. It's not rated as a car extinguisher as it won't work in freezing conditions - but my Ford Focus ST is from 2006. It will hardly catch fire when cold anyway.
Horns get so much rain coming to them, renewing old ones is a better approach to begin with. I swapped my failing OEM metal horns at the time with a relatively cheap plastic replacement set (aftermarket, but Lucas branded anyway). Thumbs up for your honesty: everybody makes mistakes from time to time (I slightly dented the fuel tank the same way)
One of the nice things about British wiring is that because most of the cars in Britain were produced by BLM, you almost have a national wiring color standard. (yeah, sure English Fords are the odd ones out) Comparing Jaguar, MG, Triumph, Austin and all the little spin-off brands like Riley, etc., all the lighting circuits have the same colors, all the Horns and Heater circuits have the same colors. It really makes it simple to diagnose British car electrical circuits and find your way around a wiring harness.
I agree, the original Lucus switches are way better than new aftermarket made in China or India. Water intrusion, currosion or poor grounds are the culprit for horn issues. On occasion the contract on the horn button can be the issue.
The two horns use quite some current. In order to protect the switch on the steering wheel it is best to insert a relay. I'm not sure whether you have this already installed on your car.
I'm surprised that the Lucas electrical systems on the old British cars are that simple! I own a '67 MGB and its wiring is not that much different from your 1980 MGB; only real difference is your car just has a few more components, so it's not that difficult. I understand how frustrating it is when you find out that the issue to a non-functioning instrument is a broken/corroded wire or just some crappy bodge job done by the PO as they could've just searched for a diagram corresponding to the year of vehicle. I ran into many splices as well; done by the PO such as the ignition white-red wire not going straight to the push-button solenoid as it should, or the heater fan switch not wired correctly. I wish you the best of luck in finding a radiator for that car, as it is not really that difficult to find one in the UK/Ireland/Scotland, depending in what region you're in.
I'd gladly trade your radiator woes for mine. My B caught fire during the last bit of welding and I'm sourcing a doner car for a whole damn interior >_
In my case the horns and some of the front lights on my MGB failed to work due to corrosion in the bullet connectors that are situated under the front slam panel. These connectors are right in the firing line for water and road dirt so it's no surprise they suffer. In the past the connection sleeves were made from plated brass and whilst it still corroded it was possible to pull them apart and clean them up. Nowadays most of the bullet connectors I have sourced come from China and are made from plated steel which rusts pretty quickly in the presence of salt, water and oxygen. The iron oxide then expands and it becomes impossible to separate the connectors. If anyone knows a source of brass bullet sleeves please let us all know.
