The headlight switches in the things are rubbish, so it could be dirty contacts or the switch is beginning to melt down.
But you'll need the check the headlight lift relays and the earthing points too.
A lot of these cars (depending on market) also have a "Pektron" unit fitted, this provides a delay in lowering the headlights for flashing. This could also be the source of your woes.
Whilst these cars have relays in the headlight lifting circuit, Stupidly they don't have any on the actual headlight cricuits!

This is the reason for headlight switch meltdown, as all the current used by the lights has to pass through the switch. You should fit relays to the light circuits.
Here are some threads that might help:
http://tr7triumph.com/forum/viewtopic.php?f=20&t=23029http://tr7triumph.com/forum/viewtopic.php?f=20&t=20493
"Keep calm, relax, take a deep breath, focus on the problem & PULL THE BLOODY TRIGGER"
'80 Triumph TR7.
'97 Ford Falcon Longreach 'S' ute,
'98 MG-F.
'83 Jaguar XJ6 Sovereign S3.