I think Lucas made at least 3 basic types of 12V coil, they are rated with diferent high voltage outputs: LA12 = Standard coil, 20KV output.(Factory fitted to cars like Morris minor etc.,) HA12 = High output coil, 30KV output (Factory fitted to MG, + other sports cars). SA12 = Sports coil, 40KV output, usually anodised in pale gold. Most likely aftermarket / motorsport fitment. There are probably various versions of all the above w.r.t. LT terminals (screw posts or Lucar tags) and the HT output (Screw-in acorn, or push-in type) which presumably result in different coil part numbers. It is not always an advantage to use the 40KV Sports coil, as the higher output can find insulation weaknesses and lead to HT-tracking (e.g. hairline crack in distributor-cap may be just OK at 20KV but not OK at 40KV). LT Polarity is important to ensure the spark jumps in the correct direction when points are opened. For example in a positive earth car, the CB terminal is + Positive and SW is - Negative. Sometimes this is forgotten when changing polarity of a car and although the systemstill works, it could result in shortened lifetime of contact breakers + plug electrodes. Giles Lacey Posted by lacey giles 11/02/2015 15:09:11
