The Lucas D142, 8'' headlight, fitted to all heavyweight models, came in two versions, flat & domed glass. Both had the plain shell (bucket) with no instrument cutout. Most common is the flat glass variety, the rim having a rolled front edge & a long curved flat clip with a rolled front edge to retain it. The clip is retained in the shell with a straight length of wire. During the 1938 season Triumph also used a domed glass headlamp as supplies from Lucas allowed. This rim was retained with a 'two finger' chromed, cast alloy clasp which relied on a 'W' clip retained in the shell. The shells are therefore not interchangeable, differing in the clip retaining arrangement & cutout underneath. In addition, both versions came in two different materials: The chrome shells on Tigers & Speedtwin were brass whereas the painted shells on the Deluxe range (5H/6S) were steel. The steel shells seemed to have survived better as the brass becomes brittle & splits. The correct lengths for the headlamp struts on the '37/'38 models are 4'' at top, 7'' bottom, between centres. However, the new number-plate for 1939 seems to have necessitated a longer lower strut at 71/2'' to clear the headlamp.

The tail light was always the Lucas MT110 although pre-war versions differed slightly in having a 'jewelled' glass lense, whereas post-war versions had a cheaper domed, plastic lense. For inspection lamps and ammeters see 'Instrument panels'.