No Headlights Dimmer Switch Disintegrated !

[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.

[BigBird05]

So in your analogy you wouldn't replace a burned out fuse link. You would just hard wire it to the + source.

[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

[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.