Lucas 149SA 47SA Ignition Switches
Ignition Switches
The Lucas 3 and 4-position ignition switches designated as 149SA and 47SA are very similar in design and appearance. Used extensively in the 1960s and through the early 1980s, Lucas supplied the British automotive and motorcycle industries with many common switches. The 47SA was most commonly associated with automotive applications, while the 149SA was used in various motorcycle applications in the 1970s. Let’s take a look at some of the features that differentiate the two switches:
47SA 3-Position Ignition Switch
The 47SA switch is a core with varying switch positions and circuitry, depending on the part number and intended applications. Common Lucas automotive part numbers are 34680, 31912, 31973, among others. These were used in Jaguar, MG, Triumph, Lotus, Mini, etc. and have the usual anti-clockwise detent for parking lights, center “off” position, first detent clockwise for ignition and running lights, and a third position which is sprung loaded to engage the starter solenoid. When the engine starts, the key is released and returns to the first detent.
There are variations in the terminal arrangement on the backside of the switch, which is usually identified with a white plastic backing plate and faint identifying terminal numbers molded into the plate. There is at least one of the 47SA-type switches used on late-model Triumph TR7 and T140 motorcycles from 1979-onward (according to the suppliers, but not confirmed in the parts catalogs), Lucas part number 35351. This switch is configured with an anti-clockwise detent for running lights only, center “off” position, and a clockwise detent for ignition and lights, which were switched to either pilot (for starting) or main headlamp with a sliding switch on the right-hand 187SA switch console.
The Lucas 35351 ignition switch is not recommended for use on the earlier oil-in-frame BSA and Triumph models using 169SA switch consoles.
Genuine Lucas 47SA Ignition/Lighting Switch Body Triumph T140E T140D 1979-1983 PN# 35351-2nd
Original price was: $36.10.$32.49Current price is: $32.49.
149SA 4-Position Ignition Switch
The 149SA switch shares a similar body shape and dimensions as the 47SA, but is currently manufactured with a brown backing plate, similar to the “bakelite” plate on the Lucas factory originals. The terminal numbers are stamped into the backing plate for easy identification of terminals 1-4. The 149SA switch is associated with Lucas part numbers 39784, 30552, 39565, and 54531899. This switch was specified for the 1971-1972 BSA and Triumph 650 twins, as well as the 1971-1975 Norton Commando models and the 1975 Triumph T160 Trident.
Curiously, the 1979-onward Triumph parts catalogs list the 99-7055 (54531899) ignition switch as original fitment, in spite of the 35351 recommendation from Lucas. The functions are as follows: key switched anti-clockwise for running lights, center position “off”, 1st position clockwise ignition only, and 2nd position clockwise ignition plus running lights. This switch can also be fitted to the 1979-onward Triumph 750 twins with the later 187SA switch consoles. The 149SA 4-position switch is in fact denoted in the factory workshop wiring diagram for the 1979-1983 kickstart and electric-start models.
The Takeaway
Now that we understand the differences between the 47SA and 149SA ignition switches, we can make some recommendations for the intended uses of each switch. The 149SA switch (39784, 30552, 39565, 54531899, 19-1904, 99-7055, 06-2058) can be used in all of the applications where a 4-position master switch is specified, confirmed by the factory parts catalogs.
The 47SA (35351) switch is not found in the parts books because it was not originally specified for use in Triumph, BSA, or Norton motorcycles, but is a suitable replacement master switch for the 1979-onward Triumph 750 models when the 149SA is not available or when an economy switch is desired. We recommend using the original 149SA switch for best results when following the original wiring diagrams found in the Triumph, BSA, and Norton factory workshop manuals. I hope you have enjoyed this article and have found it to be informative.
Dave Porter – Tech and Customer Support at The Bonneville Shop