Headlights go out when I switch to brights

I have a ‘64’ Mercury Montclair. It has a 4 headlight setup, I replaced the 2 inner headlights and there is no change. The lights work fine, until I step on the floor switch and I have no lights at all.
Thanks in advance.

Josh Lindstrom A.K.A. Godfather

When you step on the floor switch, it toggles a relay that directs the power either to the high beams or the low beams. That relay has most likely failed. If it still clicks, you may be able to locate it by following the sound when you press the dimmer button on the floor. If the relay no longer clicks, good luck finding it. Some really old mechanic may know where it is.

Another thing that sometimes happens is that the plug on the relay gets corroded and it overheats and melts.

Your vehicle doesn’t have a relay that controls the high/low beams. This is controlled thru the dimmer switch.

The dimmer switch requires replacement.


thanks much Sir.

With a 4 headlight set up the outer bulbs have 2 filaments, one for high and one for low…The inner lights have only the high beam filament .When you turn on the highs all 4 should light up…Agree with tester as your car has the same setup as my 59 T-bird…No relays. When on low beams the floor switch only supplies power to the 2 outer low beam lights…When you activate the high beams the switch breaks the low beam circuit ( 2 outer low beams ) and supplies power to all four headlamps.( the high beams only ) This is very easy to trouble shoot…

When using the high beams you should have 12 volts going into and out of the switch…if not then its the switch…if you do show voltage on both ends of the switch it may be a high beam wiring problem between the switch and lights…I am still going with the switch.These switches were prone to failure as being on the floor, moisture would cause them to rust On my t-bird my switch was stuck in the high beams and had the opposite what you have had highs and no lows…Nice car by the way.

Concur w/@Howie32703, sounds like the floor switch has failed. It must switch between sending current to the two low beam filiaments on the outer lights, and all four high beam filaments on the outer and inner lights. It would make sense that side of the switch would fail first, as it handles more current.

Replace the dimmer switch.

Oops, sorry. I would claim to be too young to remember a '64 but several here know better.

Usually it’s the dimmer switch on the old cars. You can remove the connector and look at the terminals; cleaning them may help. Most times we just changed them.

I agree with everyone else that suggested the floor dimmer switch. I replaced them on a couple of cars I had. One thing you may encounter is the bolts being rusted and the switch itself rusted to the floor.