| Also known as | 315738, F3158 |
| Diagram | Fig. 15 — SWINGING ARM, SUSPENSION UNITS AND CHAINGUARD · ref 42 |
| Subsystem | primary |
| Listed in parts books | 1963–1965, 1967–1970, 1974 |
| Also fits (as replacement) | 1963–1965, 1967–1968 · for 315738 |
Spring (315738)
Small return spring for the rear brake light switch on Triumph twins, PN 82-3158 (315738, F3158).
This is the spring that works with the rear brake light switch, part number 82-3158, also found in older records as 315738 or F3158. The parts books place it in the swinging arm and suspension unit figures, right alongside the rear brake and chainguard hardware where the brake light switch mounts.
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It's a small return spring that keeps tension on the switch mechanism so the brake light comes on and goes off cleanly when you work the rear brake. Cheap to overlook, but if it's stretched out, missing, or rusted through, you'll get an intermittent or stuck brake light.
Our catalog record shows this one appearing across entries from 1968 to 1974, and it carries the same factory number, 315738, straight through, so there's no separate old-versus-new part to sort out here. Worth checking the switch and spring together since they're a matched, low-cost item to replace as a set.
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