At the risk of beating a subject to death, it just occurred to me that
the dashlights are not fed from the dash volt stab, but from the
headlight switch. Doh, its obvious of course, but that means
calculations of resistor value for led should be based on 12.65-14 V
and not 10 V.

(I risk making another blunder in assuming that the max output from
headlight switch potentiometer/rheostat is in fact battery/alternator
output, I suppose I could measure it !)

So my compounded blunder with my last expt using a 3.8 forward voltage
led actually did use the correct resistor (520 ohm).

Alistair

'82 westy, diesel converted to gas in '94
http://www.members.shaw.ca/albell/