CRM: that is correct because the ballast open circuit voltage is diffent between the mercury vapour and metal haldie bulb.

Paul ,, i will suggest to recheck the ballast to see what the label it say what type of lamp it required to use if say 'M-51" or S-51 please watch out the ballast destaion number you can not interchange both bulbs at all otherwise you will damged the running gears.

merci , marc

Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)