Depends on year of manufacture. Usually it's a small square block with 2 yellow and a red wire coming out of it, attached to the cowling.
On some Westwoods, the rectifier diode is built in to the wiring harness - there will be 2 yellow wires emerging from under the cowling, with a 'bump' under some heat-shrink where it joins the harness. The bump is the rectifier diode.
(phil_saunders(a)bigfoot.com)
Phil Saunders, June 2013
