Recently my headlights start flashing in their.

If the alternator is charging at 15 V, it is overchargning and that could be the problem of the headlights flashing, due to current spike. A charging fault can result in erratic electrical controls.

MY SWITCH IS IN THE FLOORWHERE IT HAS BEEN SINCE THE '40s

YOURS WAS PROBABLY CHANGED FROM THE FLOOR AND PUT UP ON THE COLUMN SOMEWHERE.....MOST LIKELY WITHIN 5 YEARS PRIOR TO YOURS BEING MANUFACTURED

THIS IS WHAT YOURS LOOKS LIKE NOW!

http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_dimmer-switch-bwd_5970350-p?searchTerm=dimmer+switch

IT MOST LIKELY LOOKED VERY SIMILAR TO MINE, WHEN IT WAS DOWN YONDER IN THE FLOOR----PRESENTLY YOURS HAS 3 WIRES IN THE CONNECTOR (JUST LIKE MINE) ONE IS "HOT" OFF OF THE LIGHT SWITCH, WHEN IT IS ONONE GOES TO THE "LOW BEAMS"----THE OTHER TO THE "HIGH BEAMS"

SEE MY LINK--THIS MAY BE YOUR FATE---AS IT SOUNDS SOMEWHAT SIMILAR

SEE MY ANSWER "DECEMBER 3" ON THIS POST

THE MEDIC

The reason the headlights are flahsing is there is built in circuit breaker in the headlight switch, you have a short in your system someplace and aawire is touching it cold be the dimmer switch or a wire that has rubbed through and is hitting a ground somewhere. If this car has been in a wreck recently body shops are notorious for just twisting stuff together to make it work an dthat cold be your problem.