1968 oldsmobile delta 88 with the 455 . I believe the high beam switch on the floor is not working. Low beam lights are working but when I click the floor switch the low beams stay on but both of the high beams are not working . The light on the dashboard comes on but again no high beam headlights. Wondering what the cause could be . Bad switch ? Bad fuse?

 

First thing is check that both of the high beam lamps are good. Next ? Are the low beams changing from low to high beams when you actuate the dimmer switch, or are they staying on low beam? Let us know and then we'll troubleshoot further.

If the dimmer switch is bad, recommend trying to find a new old stock switch, either Delco-Remy, Standard, NAPA Echlin or similar.

 

The low beam bulbs have two separate filaments, one powered in the low beam position, one powered in the high beam position. Are you SURE both high beam bulbs aren't just burned out? Did you check for power at the connector to each high beam bulb? At the high beam terminal coming out of the dimmer switch (green wire)?

 

The fact that the high beam indicator on the dash comes on tells you the dimmer switch is working.

Before doing anything else, check for power on the green wire of the drivers side high beam headlight. If it has power, check the passenger side. If both have power, replace the high beam headlights.

 

12v test light. Should be in everyone's tool set.

Connect the clip to ground, then touch the probe to the terminal in the headlight plug as Matt suggested.

 

Ok so both of the filaments on the low beam bulbs are working but I have to buy that tester to test the high beams as suggested . I will report back once I get it .

 

Harbor Freight, Northern Tool or any parts store should have one for less than $10. It's a handy thing when doing any kind of electrical work.

Since the outer lights switch from low to high and the dash indicator works, either the high beams are burned out or their plugs might be corroded. Let us know what you find.

 

If the high beam filaments in the low beam bulbs are working, chances are both high beam bulbs are burned out. There's one wire that runs from the firewall connector to the LH low beam bulb. That wire is spliced at the plug with one wire running to the LH high beam and one to the RH low beam. The RH low beam feeds the RH high beam. If that splice were bad, the high beam filament in the RH low beam bulb would not work. Each high beam bulb has a ground wire that runs to the core support, but again the ground point for the high beam and low beam bulb on each side is common, so it is very unlikely that the ground would be bad (but not impossible). My money is on the bulbs.

 

You can run jumper wires from the low beam plug to the high beam lamps and check for bad bulbs or vice versa.

 

Bought a 12 v test light and both high beam headlights have power . Ordered 2 new high beam lights hopefully the issue is resolved after this . What would cause both high beams to be out at the same time ? Is that a common thing to happen with these older cars ?

 

Well, both being out now doesn't mean they both failed at the same time. It's possible someone drove it with one high beam out for 10 years before the other one failed.

 

They only last so long and both being out is not uncommon.

 

Filament could have been both weak from age, when you turned on the brights and 12V went through the filaments perhaps they both 'popped' and burned out.

 

New lights have been installed and the problem has been resolved . Thanks guys .

 

Good troubleshooting! Glad you can see at night again!