Miller Vincent Tail light wiring 6v ideas anyone???

wired up a vincent tailight (has 2 single filament bulbs, one for tail, one for stop) to the enfield. it's six volt so i put 2 single filament 6v bulbs in (shop gave me 6v/8w ones). won't light up.
I've put my wire tester on the bulb contacts, and it lights up, so there's power to the contacts in the light housing. but the bulbs wont light up. it had a dual filament lucas type light before this.
I haven't had any trouble using 2 single filament lights in place of a dual filament before, usually plug n play, so has me puzzled.
and yes the light housing is bolted up tight so Im assuming it's earthing okay?
any ideas? have pm'd Scotty so hopin to get some advice from the expert, but thought I'd chuck it on here anyways, in case some smart cookie has an idea

shoot... test the bulbs? check that they are also making correct contact

jon61 wrote:

shoot... test the bulbs? check that they are also making correct contact

thanx Jon, yep will do. they look fine, but it's always better to eliminate these things aye
it seems strange cos my tester light lites up when it touches the contacts...
also thinking,
-try separate wire for ground to see if helps (my test light lites up & that is grounded so ... maybe the bulbs are just not grounded enough?)
-put digital tester on to see what volts/amps comin thru
-check back further down the wiring to see how the stoplight switch is wired in
-or hope that Scotty has an idea

just tested the bulbs, and they work.
so yeah, im thinkin a bad ground, or loose connect in the housing somewhere, tommorow is another day
gives the paint on the tins time to dry anyway

Solved. The bracket I made for the light is mounted to the lower shock mount, the rubber from the shock mount bushing was stopping the housing from grounding - I hadn't even thought about the rubber bush.
Ran an earth wire & now it works! Cool.