Headlights cut out completely after hitting high beam dimmer switch
 

Took my 71 C20 out for a stroll around the block this evening.
When I hit the dimmer switch for the high beams - the headlights cut out completely.
All other lights are working fine. I didn't dig into the issue tonight. I plan to get back out there tomorrow and see if I can track down a faulty wire or ground.

Any ideas?

Re: Headlights cut out completely after hitting high beam dimmer switch
 

I would start troubleshooting at the highbeam switch. It's common for the terminal connections on the switch to corrode and then the overheat the wiring.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

x2 -- the dimmer switch on the floor, aka highbeam switch, lives in a poor environment and is a common failure spot.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

If you have higher wattage Halogens in the truck the dimmer switches don't survive well.

I put relays on both low and high beam circuts on my 71 to cut down on the load through the switch (s) After replacing the switch about every four or five months but I am running 55/100 H-4 bulbs.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

I would start by replacing the dimmer switch. They are like $5.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

There are no fuses for the headlights, so don't wear yourself out looking for one. The headlight switch has a built-in circuit breaker that automatically resets itself. Don't use W.A.G. techniques, and parts slinging hoping something sticks. Go here:

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

and download the proper wiring diagram for your truck. Start with the dimmer switch, use a voltmeter or 12V test light to check for continuity, bad switches, bad/corroded connections, burned/broken wires, etc...

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Yeah. LMC lists p/n: 36-0620 for $5.95.
Funny, I needed one right now -- last week -- and bought a Dimmer Switch from O'Reilly's for $26.38. [Incl tax, and w/ Mil Disc]. It was made by Standard and had a ''Lifetime Warranty.''
Still made in Taiwan. [P/N: STD DS72]

The last one was from 7/17, so almost 5 years in a daily driver isn't bad for a part that gets stomped-on multiple times a night.

awbanks: I had your exact gripe, and R&R'ed the Dimmer Switch and that got it.
While you're down there inspect the wiring to the plug and terminals, but most likerly it's just the Switch.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

First thing I would do is check for 12v at the headlights.

From my experience with LMC that $6 switch will be the same or more than Orielly's after shipping, Then there is the issue if it is actually in stock and when they will ship.

The 51 year old switch in my 72 still works. Funny how expectations have changed.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

I've had good luck with replacing the dimmer switch first. That tends to be the most common cause of your issue. Or to put it differently, the most common sign of a bad dimmer switch is the headlights cancelled out when you hit hi-beams. Don't throw the original out until you see the new one was the fix. If by a less likely chance you have some other issue, you'd be best continuing use of the original. But, mostly likely when to remove that switch you will see it has become right crusty.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Thanks for linking the wiring diagram. That will be a helpful resource. I plan to check with a test light before moving forward with any replacement switches...

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Good to know Orielly has some in stock. I find LMC Truck has some great deals - but sometimes can get you with shipping costs. Looks like they've got it for $5.95 and $5 shipping to me

Re: Headlights cut out completely after hitting high beam dimmer switch
 

I fought exactly this on my 70 last year. Replaced the switch a couple times and it would work. And then not. And then would. Always lost hi beams. Is it original wiring? Or rewired? My truck was a full frame off, and I used an AAW kit to rewire. On the bulkhead block from the inside of the cab, the little metal tab that holds the terminal in the block was never sprung out enough to catch apparently on the hi beam terminal. So when the engine bay side of the bulkhead block was installed, it pushed that one back just enough that it would barely touch but vibrate a little and intermittently loose contact.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

As mentioned, the dimmer switch on floor is most likely suspect. If it is lose, tighten the hold down screws.

IMHO installing a headlight relay harness is a good idea on any of the 50-70's cars, trucks. LMC sells one. Plug and play, no cutting any wires. It removes the full 12v load off the headlight switch, so headlights and ALL lights are brighter

This is where I installed mine. Just drilled 2 holes to mount relays

.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Lost my headlights in 2011 at 5:30 A.M. My O.E. dimmer switch lasted 42 years . Paid $7 for a new one back then . Been fine ever since . Thanks

Re: Headlights cut out completely after hitting high beam dimmer switch
 

MN location. (Like me).
Most likely a green, furry dimmer switch connector.

Step 1: Take the connector off the dimmer switch. Look at the connections.
Step 2: Spray with contact cleaner.
Step 3: Re-connect.
You probably just fixed your headlights but I'd do more...

Step 4: As 72SB points out, research this site for "Headlight Relay Upgrade" then roll your own or buy a pre-made wiring harness that uses relays to power your headlights instead of elevendy billion miles of 16 or 18 gauge GM stock wire.

All those miles of stock, too small now dry and brittle wire only gets about 10.5 volts to your headlights.

Using relays to drive your headlights with juice straight off the battery not only puts 14.something volts to your headlights making them brighter, it also saves on your headlight switch which is more money and a larger PITA to replace.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Thanks everyone for the information! The wiring harness color graphic will be extremely helpful in the future.
It ended up being a faulty dimmer switch. Ended up going with Orielly Auto's replacement for now as 68OrangeSunrise stated and everything works great now.

I did find that the headlight wiring will need some work up front as someone did a poor job of fixing the headlight wire at some point in time.
I will look at adding a relay.

This is why I love this forum! Thank you all for your wisdom and insight. :thumbs:

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Glad you got it fixed, and thanks for the update!

If / when you do the relay mod, you'll need two -- one for low beams, & one for high beams.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Just went through this. As others have said ,look at the dimmer switch. That was the problem on mine. I took mine apart and cleaned it. Works perfect now. I would try and repair original. They are well made. Good luck

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Happy to help. The 67/72 Forum is a main reason why my Over Fifty trucks still run.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

Just FYI that switch is an AC Delco D808 and can be bought today on Amazon for $12. I don't know if the Delcos are any better than a generic parts store one, but it's an option.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

I had this happen on a road trip going through the mountains at night in my 69 Vette. After pressing on the high beam switch a few times the headlights worked again. Probably corrosion in the switch from not being used much.

Re: Headlights cut out completely after hitting high beam dimmer switch
 

I'm going to pull apart the old one [from 2017] and see if it can be refurbished.
Looks like one of the 2 side tangs lost its angle and that allows the cap to come up higher than it should from spring pressure.
In Arizona we see very little corrosion. But the Jimmy, because of its convertible nature has a lot more cabin leaks than the Stepside's cab, even though it's 3 years older.