headlight relay

[duplaga1952]

i've heard about headlight and horn relays . where else would a relay help the electical system ? do the brake lights need any assistance ?

 

[JPSmit]

I'm doing horn, headlights and driving light. I don't think brake lights are worth it - not on that long - was kind of kicking around fan and even wiper but don't think I will. Basically, it is anything that is a high current draw and resistance in the switch

 

[tweety]

Instead of rewiring the tail lights (all of the them) with relays, I replace the bulbs with LED's. Much brighter and far lower current draw..... So far so good..

 

[highhilleer]

Instead of rewiring the tail lights (all of the them) with relays, I replace the bulbs with LED's. Much brighter and far lower current draw..... So far so good..

Do they flash right? I've heard that sometimes the flasher unit doesn't work right without a certain amount of resistance which led lights lack.

 

[Guest]

I have led front turn and parking lights. Mine didn't wok with the original flasher unit. I didn't change the rears. I went to the local corporate third world autoparts store and purchased what is called a "2 prong heavy duty flasher relay) and replaced the original one with that. They do flash faster than oiginal. There's also a HD flasher unit that I saw in Yogi's online- tailored to LED's it also allows for adjusting the speed of the flash.

 

[Sarastro]

I didn't know that LED replacements were available--who sells them?

I'm not surprised that the stock flasher might not work with them. LEDs draw quite a bit less current, and the flasher requires a certain amount to work right.

 

[Pythias]

The only reason to use relays for the headlights is IF you are using NON-STOCK lighting, like H4 or H6 bulbs. The stock headlight switch was designed to carry the current of standard sealed beams. Same with the horn. the stock ring will carry all the current needed for even dual horns, as it was DESIGNED to do. ..

It may be important to discuss the WHY of LED lights not functioning properly with the stock flasher unit. It is a bimetallic design. That is, the current flow causes the element to heat up. when it does it curls away from making contact due to the difference in thermal expansion of the two metals of which it is composed. When the current stops flowing the metal cools, and it goes back to it original position, making contact... It needs ALL the current flow through BOTH bulbs, front and back to function as designed. That's how you know a bulb is burned out. When you turn on the signal, it stays on rather than blinking due to insufficient current flow to cause the the strip to curl. And THAT is the problem with LED replacements. they are LOW CURRENT devices, and don't draw enough to heat the strip.

 

[tweety]

I did change my flasher relay to an electronic type, flashes fine with LED's front and back. Hazzards work ok too

I get all of MY LED's from www.superbrightleds.com they have TONS of stuff and lots of technical specs to do with their products. I've bought lots of stuff from them with good results.

 

[JPSmit]

The only reason to use relays for the headlights is IF you are using NON-STOCK lighting, like H4 or H6 bulbs. The stock headlight switch was designed to carry the current of standard sealed beams. Same with the horn. the stock ring will carry all the current needed for even dual horns, as it was DESIGNED to do. ..

My understanding was that the other reason to use relays was that over time wiring and especially switches age and as they do the resistance in them increases thereby lowering brightness of the bulbs and also increasing heat

 

[tosoutherncars]

Your understanding was right, JP.

These switches were NOT designed to carry full current for fifty or sixty years. And, these are cars that were built as cheaply as humanly possible. (No trunk or door handles, anyone?) Priced out a NOS switch lately? Ouch.

There are valid reasons to upgrade to relays, even on stock systems. Just like there are valid reasons to use tapered roller bearings in the place of old ball bearings, or poly bushings to replace collapsed rubber. No, you don't HAVE to. Yes, it should work fine the other way. And yes, relays can improve stock lighting.

 

[dklawson]

Your understanding was right, JP.
These switches were NOT designed to carry full current for fifty or sixty years. And, these are cars that were built as cheaply as humanly possible. (No trunk or door handles, anyone?) Priced out a NOS switch lately? Ouch.

I agree completely. That's the reason I have a relay panel in the Mini. The switches are way too expensive to expose to the current they were originally designed for. The turning point for me was the horn contact which in spite of all my best efforts to clean... would NOT pass enough current and got extremely hot. A relay to the horn circuit restored proper operation and started my move towards headlight and reverse light relays.

 

[Pythias]

The amount of current that contacts can carry is NOT dependent on AGE. It IS dependent on the SIZE of the contact area. This does not change with age. While the spring mechanism may wear out due to the duty cycle, and thus weaken the amount of pressure that holds the points together, (Switches DO wear out) the size of the contact area is NOT matterialy affected. Wire does NOT wear out either. The size, and thus the current carrying capability does not change with age. The contact point at the terminations may become corroded, increasing the resistance AT THAT POINT, but the resistance of the wire itself does not change. The insulation, being plastic, or rubber may become brittle with age, and crack when moved, but unless disturbed physically, will remain in place and perform its function.

If it makes one feel better to use relays and complicate the wiring of one's car, go right ahead. One more point to trouble shoot never really hurt anything. IF one want to run larger wires to lessen resistance, do it. But do them for the right reason, one WANTS to.

 

[Bayless]

But those contacts do pit, burn and corrode just a little each time they are used and the amount of current determines the severity of that deterioration. Any switch, given enough time, will eventually fail. Using cheap relays to carry the high load circuits simply delays the time when the respective switches will eventually fail, probably well beyond our lifetimes.

 

[dklawson]

If it makes one feel better to use relays and complicate the wiring of one's car, go right ahead. One more point to trouble shoot never really hurt anything. IF one want to run larger wires to lessen resistance, do it. But do them for the right reason, one WANTS to.

As Bayless said, each time you use the switch it gets one step closer to the end of its useful life. As there is less and less sound contact material left the resistance heating at the contacts increases. This is a problem that effects the plastic rocker switches more than the metal toggle switches. You are correct that it has nothing to do with the wires themselves.

I have done the relay conversion and will probably do it to all my older cars eventually. Yes, it's because I "want" to, but more importantly because it extends the useful life of expensive or hard to find components. Bosch/ISO relays are very common and inexpensive by comparison. Troubleshooting a relay involves plugging a new one in and I do keep a spare in the boot.

 

[Sarastro]

This is especially true of switches that cut DC current. If you look at switch specs, the current spec invariably is lower for dc than ac. The reason is that ac voltage drops every half cycle, helping to extinguish the arc that occurs at the contacts as the switch is opened. That doesn't happen in dc, so the arc that occurs when the switch is opened lasts longer and therefore burns more. This is especially bad for the horn, since it's an inductive load and therefore creates an unusually high voltage at the switch contacts (i.e., horn button) when the switch breaks the circuit.

I've added a horn relay and one other, for miscellaneous additional electrical parts. I plan to add one for the lights, too, when I get a chance.

By the way, my bugeye wiring diagram does show a relay for the dual-horn option but not for the single horn.