i don't know what the problem is!?

[stevingreen]

I have just recently done a ground up restoration on a 1969 gmc 3/4 ton 4x4 and when i drive with my brights on, after about 5 mins. they start flashing on and off really fast and just start freaking out like that. i will turn the brights off for a while, then turn them back on and they will work for about 5 mins. again until they do this again... what can be the problem!! this is really frusterating for me!!