No Headlights Dimmer Switch Disintegrated !

[54blackhornet]

I noticed that the headlights weren’t working so I started with the dimmer switch, because I read it’s a typical problem area on GM vehicles of this vintage. Just getting the plug off was a pita because of the corrosion. When it finally came off I noticed the part of the switch came with it. The screws where corroded also but BP worked its magic. After getting the switch off the floor I found this. Suggestions on replacement?

[Stocker]

You heard right, that's a common problem area -- though yours may be worse than most. Should be able to get a new dimmer switch at any auto parts store.

[BigBird05]

Look into running your head lights thru relays and cut down on the amount of amperage that the switch will have to carry. I am going to run relays on my head lights, tail lights, turn signals starter solenoid and Ign 1 to the fuse box because so many people report ign switch failures.

[Sheepdip]

Originally Posted by BigBird05

Look into running your head lights thru relays and cut down on the amount of amperage that the switch will have to carry. I am going to run relays on my head lights, tail lights, turn signals starter solenoid and Ign 1 to the fuse box because so many people report ign switch failures.

^^^^^^^^^^^^^^^^This^^^^^^^^^^^^^^^^^^^

Is money well spent, all of my older vehicles were either wired or
converted to a complete relay system. This is where modern
technology is good for these old classics, besides I'm all about
function/dependability.

L.E.D.s are another plus to the system wherever possible to cut down
on amp/current draw

[burnin oil]

Originally Posted by Sheepdip

^^^^^^^^^^^^^^^^This^^^^^^^^^^^^^^^^^^^

Is money well spent, all of my older vehicles were either wired or
converted to a complete relay system. This is where modern
technology is good for these old classics, besides I'm all about
function/dependability.

L.E.D.s are another plus to the system wherever possible to cut down
on amp/current draw

Totally not needed on a stock truck. Think about how long those parts lasted before failure. The stock headlight switch ran the headlights and the added load of trailer lights also. that was part of the deign criteria back in the day.. Now that I said that, the headlight relays do work really well. For the most part this is a keep it simple affair. If you are going relay crazy why not swap everything over to constant hot with switched grounds and add a body control module? Don't go nuts over the simple things. Save the relays for things like electric fuel pumps.

[BigBird05]

Originally Posted by burnin oil

Totally not needed on a stock truck. Think about how long those parts lasted before failure. The stock headlight switch ran the headlights and the added load of trailer lights also. that was part of the deign criteria back in the day.. Now that I said that, the headlight relays do work really well. For the most part this is a keep it simple affair. If you are going relay crazy why not swap everything over to constant hot with switched grounds and add a body control module? Don't go nuts over the simple things. Save the relays for things like electric fuel pumps.

They wouldn't be necessary if the replacement parts were as good as the original parts 50 years ago. There are to many stories on here about new electrical switches only lasting a year or two.

[Stocker]

Originally Posted by burnin oil

Totally not needed on a stock truck. Think about how long those parts lasted before failure. The stock headlight switch ran the headlights and the added load of trailer lights also. that was part of the deign criteria back in the day.. Now that I said that, the headlight relays do work really well. For the most part this is a keep it simple affair. If you are going relay crazy why not swap everything over to constant hot with switched grounds and add a body control module? Don't go nuts over the simple things. Save the relays for things like electric fuel pumps.

As you said, headlight relays work well. For one thing, they deliver maximum voltage to the headlights, making them measurably brighter. This because you bypass restrictive wiring as well as the headlight switch and the floor dimmer switch.

You can do a before / after voltage comparison at the headlights to see what is gained with relays. Daniel Stern's website has some great info showing the light output in lumens at different voltages.
http://www.danielsternlighting.com/t...ys/relays.html The following is a bit long, but worth a look imho.

Why Bother With Relays?

Power for the headlights is controlled by (wait for it) the headlight switch. In almost all vehicles built through the late '90s, and quite a few built after that timeframe, all headlamp current runs through the switch. That is: long lengths of thin wire to and from the switch, which contains tiny contacts. All of this adds up to a surprising amount of resistive voltage drop, which takes a big bite out of headlamp output.

In many cases, the thin factory wires are inadequate even for the standard original-equipment headlamps. There's a large element of automaker cost-cutting involved; it might sound like a joke to say they figure headlamps are only used at night, so that's a 50% usage duty, so they cut the wire gauge in half, but it's actually pretty close to how these kinds of decisions are often made in the auto industry where just about every last fraction of a cent that can be shaved from the build cost, will be.

And science has yet to give us the wiring, connections, and switch contacts that improve with age; in fact they do the opposite.

Headlamp bulb light output is severely compromised with decreased voltage. The drop in light output is not linear, it is exponential to the power 3.4. For example, let's consider a bulb with a rated output of 1000 lumens at 12.8 Volts and look what happens when it is operated at different voltages:

10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens ←Rated output voltage
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens ←Rated life voltage
14.5V : 1528 lumens
(Outside North America bulb output and lifespan are both rated at 13.2v, but the effect of voltage drop is the same).

When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal! It is quite common for factory headlamp circuits to produce this kind of voltage drop, especially once they're no longer brand new and the connections have accumulated some corrosion and dirt.

[lil hoodlum]

Originally Posted by burnin oil

Totally not needed on a stock truck. Think about how long those parts lasted before failure. The stock headlight switch ran the headlights and the added load of trailer lights also. that was part of the deign criteria back in the day.. Now that I said that, the headlight relays do work really well. For the most part this is a keep it simple affair. If you are going relay crazy why not swap everything over to constant hot with switched grounds and add a body control module? Don't go nuts over the simple things. Save the relays for things like electric fuel pumps.

I am running the stock type headlight and dimmer switch in my 68 C10 daily driver for 24 years now. They work as they should but sometimes it seems as if my headlights "pulse" at night while idling. It is a little annoying and have been considering doing the relay upgrade because I have had to replace the headlight switch a few times. I do have a aftermarket wiring harness installed and all of the necessary grounds. I am still running the factory 65 Amp alternator too.

[mr48chev]

Originally Posted by burnin oil

Totally not needed on a stock truck. Think about how long those parts lasted before failure. The stock headlight switch ran the headlights and the added load of trailer lights also. that was part of the deign criteria back in the day.. Now that I said that, the headlight relays do work really well. For the most part this is a keep it simple affair. If you are going relay crazy why not swap everything over to constant hot with switched grounds and add a body control module? Don't go nuts over the simple things. Save the relays for things like electric fuel pumps.

I'm late to this party but burned out three good quality dimmer switches on my 71 with each lasting about six months. because the halogen lights draw more amps than the stock lights do.
Most of us who actually drive our trucks run halogen lights rather than the dim old original style lights.
True if you don't run Halogens you probably will never have an issue with the switches except wearing them out if you drive the truck enough.
I put relays on my lights and that ended the dimmer switch issue. The relays are on the inside of the core support next to the original external regulator and unless you are looking for them you never see them.

[Stocker]

Glad you pointed that out -- I forgot to mention it. Relays also help extend the life of the headlamp switch on the dash, for the same reasons. And they supply higher voltage to the headlamps, resulting in brighter lights. Great little mod for stock lighting, even more critical if you run higher wattage bulbs.

[54blackhornet]

Thanks fellas I guess after 50 years I can’t really complain to much ! I was hoping that I could replace the switch with a original delco part not another Chinese pos I see advertised...

[72 Super]

I just replaced mine a few months back for exact some problem. It is an AC Delco piece but I don’t believe it is made in the US as the originals were. But it works perfect though.

https://www.amazon.com/your-orders/p...ntId=DBps9j9Jp

[Stocker]

Originally Posted by 72 Super

I just replaced mine a few months back for exact some problem. It is an AC Delco piece but I don’t believe it is made in the US as the originals were. But it works perfect though.

https://www.amazon.com/your-orders/p...ntId=DBps9j9Jp

When I click on your Amazon "your-orders" it takes me to MY Amazon order page!

Maybe if you post a link to the page with the actual item....

[72 Super]

Originally Posted by Stocker

When I click on your Amazon "your-orders" it takes me to MY Amazon order page!

Maybe if you post a link to the page with the actual item....

Sorry try this one here. When I click on it from this side it works.

https://www.amazon.com/ACDelco-D808-.../dp/B000C9QXKA

['68OrangeSunshine]

You might check the status of your Dimmer Switch Pigtail too. 50 years of getting stomped is not good on any connection.

[burnin oil]

If you are truly worried about headlight output grab the relay power near the back of the alternator. This is where the system voltage is highest. The batteries job is to store 12v. I have done relay mods on a dodge mainly to simplify the addition of sport headlights and it also had a headlight switch failure. My 72 was a daily driver 72 got a replacement headlight switch maybe 10 years ago and is still fine. It has no relays installed but alot of accessories are right off the battery with large wire. I also rewired the truck myself so wire size is adequate.

[burnin oil]

I can't remember on the stock alternator but on the mid 70s style you just need to add a ring terminal to your power wire and then attach that to the stud on the back of the alternator. I believe the original alternator was the same, from memory.

[StingRay]

The dimmer switches from the van and RV chassis up into the 80's drop right in.They are usually clean and low use from the RV's.

[BigBird05]

If your going to power the relays off of the alternator ( I would advise against that ) you should use a fuse link.

[burnin oil]

Why would you advise against that? You are not using the entire headlight circuit to feed the rest of the truck. It is only picking up power at this point which has the highest voltage. It is the same concept as having a second power wire hooked up at a battery terminal. Headlight bulbs don't care if the volts are 14.4 volts and a fusible link is for amperage. We are not talking about fussy electronics that need a stable voltage to remain happy. The alternator or battery have the same potential to give the relays way more amps than needed. Dont forget Ohms law and as volts go up the amps go down as far as a given wattage is concerned. This is spoken as an electrician but not an engineer so I could have missed something.

[BigBird05]

The fusable link is for safety! It could keep the truck from burning to the ground. Would you put a new circuit in your house and wire it straight to the main line?

[54blackhornet]

I installed relays for the headlights in my MG. Two relays, one for low and high beams. I ran the power wires from the starter solenoid. With both being fused. The light output is amazing compared to the factory wiring.

[burnin oil]

No I wouldn't. That said the relay is only rated to carry so much amperage before it fails. An internal melt down of a replaceable relay would be no different than a fusible link burning in two. Either would protect a bulk of the wiring. In factory trim a fusible link does not protect an entire system but from the cab feed at the starter. It bypasses the charging, starting, and initial start of the ignition. The external regulator did have a fused line on the fender.

In the house wiring scenario this would be like adding a second main panel to the electric meter, ie a 400amp service. The initial wire is not protected until it hits the first device, the panel. In this case it would be the relay which is sacrificial (same as a fusible link) to protect the wiring down stream. Your house wiring is usually not protected from the transformer to the house. Transformers are protected on the high voltage side but rarely on the low voltage home side. At some point you have accept there is a failure point. Here you run a heavy gauge wire and let the relay let go as it would be rated far below the wires ability to carry the amperage.

A final thought here is where are the battery cables protected? They arnt and can ground out anywhere they chaff or rub on metal. I have seen plenty of burnt positive battery cables on headers.

Please don't take these comments the wrong way. It is a good conversation on the OPs question. It has the potential to let others learn and see different aspects of a system they wouldn't normally think about. Please keep it going as we are talking about different ways to skin a cat.

[burnin oil]

No. In my analogy there is no fusible link. That is truly how a house is wired. There is no wiring protectiin between the transformer and the main breaker inside your home. As far as the truck goes the factory did not install a fusible link on the charge line for years. Speaking on the internal regulators of the 73 up trucks since that wiring is fresh in my head. The hot lead of the alternator ran up to the fire wall to a junction block and then back down to the starter at the main battery cable. The stud on the starter wire was the junction for the battery cable, charge wire, and then the fusible link. The fusible link went to the cab power only. I believe that the points pickup for non HEI was also around the fusible link through the starter solenoid internally. The factory did not have any protection on the alternator charge circuit so by
Picking up power at this point the relay would actually be the circuits protective device since it would be rated at less amperage than the wiring if installed correctly. Providing proper wiring throughout the relay should burn out and not harm any of the wiring. There may be some heat damage at the relay connector as these are usually not the best connections but generally the circuit is cut by the relay leaving either side unharmed. This is also the same as the factory putting a fuse in the middle of the wire. Even if you went above and beyond and installed a fusible link at the alternator you would still have a few inches of unprotected wiring on that circuit. Physical reality of installation versus theoretical application. Either way would work but adding the second point of failure usually is a recipe for failure at the worst time. Back to the house wiring, this would be like having a breaker at the panel and then one at the plug. The load should trip the breaker and not the wiring being to small for the over current device.

I used the 73 up wiring since I remember it well and don't need to dig out a book the look up the generayor/alternator wiring difference along with the goofy circuit protection that was around the voltage regulator. Those mini glass fuses that noone seems to carry comes to mind.

If your comment was about the truck wiring and I misinterpreted that I will answer that for you. No I wouldn't replace a fusible link. In my thoughts it is easier to repair the wire at the bottom in a method that will never need attention again and then add a fuse at an assesable point with a correct size fuse. It's much easier to replace on the side of the road and not keep you stranded. Another great option is a boat circuit breaker. A wire with a blown overcurrent device will not melt down unless it's shorted so a fuse, fusible link, or breaker would all work. The slight differance in activation time is pretty mute in this application.

[54blackhornet]

Wanted to follow ! Installed a new dimmer switch I bought from GMC Paul’s. Nice quality icee, $8.00. But still no headlights. Had to clean up the dimmer switch connector, it was corroded terribly. Also where the headlights terminals. Cleaned up the main ground point on the cross member where the headlight terminals get their ground. Installed new headlights and everything is working properly now. Appreciate all the help fellas..Jack