Lost low beams

[scott_s]

1965 Valiant 200 convertible.


My hi-beam indicator in the dash doesn't work.
Yesterday morning, I flipped the foot switch back and forth to see where I left it (I live in a rural area and use the hi-beams regularly on the back roads).
The beams switched once or twice but now when I use the switch, the lights go out. The hi beams are currently working, low beams are not.
I just replaced the passenger side bulb a couple of weeks ago and everything worked fine.
What are the odds that both beams burned out at once?

I asked around on Facebook in the Plymouth Valiant group and everyone thought it was the foot switch. Picked up a new Duralast dimmer switch from Advance Auto today and installed it and got the same results.
Since I just replace the RH headlight recently, I pulled the drivers side light today.
- Tested the bulb using jumpers straight off the battery. Hi and Lo beam work.
- Tested the plug in the headlight bucket. When on HI beam, I get voltage to both sides. When on LO beam, I get nothing.

What the heck is going on here? Did I get a brand new FAULTY dimmer switch?
Are there other culprits I'm overlooking?

On a lighter note (no pun intended), I found a message left in the headlight bucket. I guess it was the previous owner?

 

[66Valiant528]

There is a single ground wire that attaches to the bucket . Perhaps it came loose? If it's not hooked up crazy things happen.

 

[toolmanmike]

Probably the dimmer switch.

 

[scott_s]

There is a single ground wire that attaches to the bucket . Perhaps it came loose? If it's not hooked up crazy things happen.

Can you tell me where that ground wire is located?

 

[scott_s]

I'm trying to think this through....

How does the dimmer switch actually, physically work? Should there always be 12V going to low beam, and then "jumped" over to connect to the hi-beam when pressed?

I'll have to pull the sill plate and roll back the carpet to get to it again, but when the headlight switch is on, power flows to the dimmer switch.
- Using a pin, check for power on the connector that attaches to the dimmer switch to see if voltage is getting through. I KNOW I get 12V to both outlets on the headlight bulb connector, in the bucket, when on HI. But I get nothing to either on LOW.
If I can see 12V flowing INTO the dimmer switch on the 3 prong connector, but not coming out on LOW, it has to be a faulty switch, right?

 

[scott_s]

Probably the dimmer switch.

I just installed a new one today. Same thing happened. I guess it COULD be faulty right out of the box. That would be my luck.

 

[Dana67Dart]

Dimmer switch 101...

It is a single pole double through switch.

There is a common terminal and a normally open and a normally closed terminal.

When the head light switch is pulled out. Power from the headlight switch goes to the common terminal of the dimmer switch.

Then when the switch is in the low beam position, power comes out of one of the terminals and goes to the low beam terminal on the bulb.

Power goes through the filament in the bulb to the common terminal on the bulb.

The common terminal is attached to ground.

When the dimmer switch is switched to high beam the power coming in on the common terminal on the switch is directed to the high beam terminal. From there it goes to the high beam terminal on the bulb, through the high beam filament, to the common terminal, to ground.


So... If the high beam work, the power flow from the headlight switch to the common ground at the bulb is all functional.

At this point I would check the low beam terminal at the dimmer switch. Then follow that wire all the way to the bulbs. Look for cuts or damage.

Also look at the plastic terminal at the dimmer switch, the metal terminals have been known to get pushed out of the plastic and not make connection.

The fact that you do not have power at the bulb in low beam supports the thought process that there is a damaged terminal wire or connector.

 

[crackedback]

Disconnect the dimmer switch from the harness. Turn HL switch on. In the connector, jump from the center terminal to the black wire, headlights on?

Yes, it's not from that point forward. If not, check the bulkhead connector for heat on the pass compartment side, then on the engine compartment side. If dead on the engine compartment side, look close at the connector.

 

[scott_s]

I forgot to mention that whoever "restored" this car did a crap job of masking stuff off when painting. Everything has paint on it, even the wiring harness.
I'll try to scrape off some paint, but can you tell me what color the wires should be? For Hi, Lo, Ground?

 

[66Valiant528]

Can you tell me where that ground wire is located?

Only 1 of the headlamp sockets had a ground pigtail. I dont remember which side it was on in our 64 Dart but it was only about 5 inches long with a ring eye and had a single small screw to mount it behind the glass bulb onto the bucket. It was loose when I did the H4 Toyota conversion kit. Only the high beams worked. Loose ground.....

 

[Dana67Dart]

Everything has paint on it, even the wiring harness.
I'll try to scrape off some paint, but can you tell me what color the wires should be? For Hi, Lo, Ground

Mymopar.com free Factory service manual, and wiring diagrams.

Classiccarwiring.com has full color laminated wiring diagrams super easy to follow.