I was talking with an acquaintance recently, and he bought a 1967 BSA but it didn' t have a battery. I told him it should be +ve earth, but before he installs the battery he should make sure, as some owners have done the -ve earth conversion. So, if you had a battery and a multimeter, how can you determine if the bike is +ve or -ve earth (ground)?
Finding type of earth on BSA
- Thread starter singring
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- Nov 20, 2004
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singring said:
[Edit]Before attempting to connect the battery-
With the ignition switched off, and with the fuse in place, set the meter to Ohms, then connect one probe to earth/ground, and the other probe to the main ignition side battery wire terminal, if the meter registers a drop from infinity to low ohms with the positive probe to ground, and a steady infinity (or close to infinity) reading when the probes are reversed, it's almost certainly a positive earth/ground system and will be the opposite for negative ground. If there's a drop in both directions then there could be short somewhere.
The simplest way would just be to check the polarity of the rectifier (+ stud), Zener and ignition coil (+ terminal = ground side).
Or, if a modern voltage control box has been fitted, check if the red box wire goes to ground (if so, it's wired +ve ground) or if the red wire connects into the main feed to the ignition switch, then it's -ve ground.
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