14-12-2021, 12:59 PM
Hi Captain Mike
As the author of the Dorset club's diagram, maybe I can shed some light (sorry). I chose to draw the circuit as the car was supplied, because if I started to include modifications then where would I stop ?
Originally, the single rear "porkpie" light housed one stop lamp and one tail lamp. The stop lamp has a wire which starts at the brake light switch under the driver's floor. The tail light has a red wire which starts at the PLC2 Lighting/Charging switch. There is a common earth to the bodywork, and because the spare wheel cover is removable this earth has to take the form of a physical wire (loomed with the other two) which connects to the bodywork at the rear. I have no information on exactly how this was done originally, but logically it would be in the lower area of the spare wheel well.
Austin, in common with nearly all car manufacturers, used the body for earth returns and there is nothing wrong with this in principle. Over the years various joints (e.g. from headlamp body to wing and wing to car) may corrode etc, and some owners have gone down the workaround route by adding earth wires either to bridge joints in the bodywork or even all the way back to the battery. I accept that in some circumstances this may be the pragmatic option, but body earthing can be made to work given good joints.
Some time later the law changed to require two tail lights. I believe this law was (unusually) retrospective, so many cars would have had tail lights added to the rear wings. Some owners would have gone further and fitted dual tail/brake lights. Some owners would have kept the pork pie working, others not. The wiring joints and routes were up to the individual. Most lights would have been designed to earth to the rear wing on which they were mounted, and rely on the wing being connected to the rest of the body by its mounting bolts.
In summary, there is no one "official" way of doing this. My preference would be to splice into the loom to the pork pie at some weather sheltered point low down in the spare wheel housing, and thoroughly tape over the splice. If you are running wires for tail and brake to wing mounted lights, it's no real hardship to include a third (local earth) wire each side and run these back to share the earth point for the pork pie, or something similar.
Finally, I have no details of how Austin connected the body earth back to the engine block/starter where the thick battery return connects. I suspect earthing was initially via the solid engine mounts, and later via the copper petrol pipe from the tank. Alternatively, there may have been a mid point "tee" connection via a lug between the battery return and the front of the battery box. These details seem to have been lost over the years. With the higher wattage bulbs that many now fit, I recommend adding a decent size braid strap somewhere between the body and the engine block
As the author of the Dorset club's diagram, maybe I can shed some light (sorry). I chose to draw the circuit as the car was supplied, because if I started to include modifications then where would I stop ?
Originally, the single rear "porkpie" light housed one stop lamp and one tail lamp. The stop lamp has a wire which starts at the brake light switch under the driver's floor. The tail light has a red wire which starts at the PLC2 Lighting/Charging switch. There is a common earth to the bodywork, and because the spare wheel cover is removable this earth has to take the form of a physical wire (loomed with the other two) which connects to the bodywork at the rear. I have no information on exactly how this was done originally, but logically it would be in the lower area of the spare wheel well.
Austin, in common with nearly all car manufacturers, used the body for earth returns and there is nothing wrong with this in principle. Over the years various joints (e.g. from headlamp body to wing and wing to car) may corrode etc, and some owners have gone down the workaround route by adding earth wires either to bridge joints in the bodywork or even all the way back to the battery. I accept that in some circumstances this may be the pragmatic option, but body earthing can be made to work given good joints.
Some time later the law changed to require two tail lights. I believe this law was (unusually) retrospective, so many cars would have had tail lights added to the rear wings. Some owners would have gone further and fitted dual tail/brake lights. Some owners would have kept the pork pie working, others not. The wiring joints and routes were up to the individual. Most lights would have been designed to earth to the rear wing on which they were mounted, and rely on the wing being connected to the rest of the body by its mounting bolts.
In summary, there is no one "official" way of doing this. My preference would be to splice into the loom to the pork pie at some weather sheltered point low down in the spare wheel housing, and thoroughly tape over the splice. If you are running wires for tail and brake to wing mounted lights, it's no real hardship to include a third (local earth) wire each side and run these back to share the earth point for the pork pie, or something similar.
Finally, I have no details of how Austin connected the body earth back to the engine block/starter where the thick battery return connects. I suspect earthing was initially via the solid engine mounts, and later via the copper petrol pipe from the tank. Alternatively, there may have been a mid point "tee" connection via a lug between the battery return and the front of the battery box. These details seem to have been lost over the years. With the higher wattage bulbs that many now fit, I recommend adding a decent size braid strap somewhere between the body and the engine block