Headlight Relay Revisited

[Rodney Bullock]

I bought a relay about a year ago and have tried to install it many times. Today I think I am on the verge of the install. This relay is a dual head light relay. It has two terminals for the head lights which might mean I can run my fog lights thought it as well( Please chim in here if I am wrong) It has two fuses inside as well. It says it's Heavy duty on the case . I took a couple of picks for everyone to look at. 

[48mirage]

It shoujd serve you well and will take the load off of your headlight switch.  You will want to run the feeds from your dimmer switch to activate the relays and your supply straight from your battery will supply the headlights.

[Alshere59]

I bought a relay about a year ago and have tried to install it many times. Today I think I am on the verge of the install. This relay is a dual head light relay. It has two terminals for the head lights which might mean I can run my fog lights thought it as well( Please chim in here if I am wrong) It has two fuses inside as well. It says it's Heavy duty on the case . I took a couple of picks for everyone to look at.headlight relay 004.JPGheadlight relay 001.JPGheadlight relay 007.JPGheadlight relay 009.JPG

I think what you have will work fine for your low and high beams but no fog lights. Basically dual head is for the low and high beams. I used two relays to do just my head lights. Here is a wiring diagram. Just scroll to the bottom.

http://www.mgexperie...relays_revb.pdf

 

Hope this helps.

It looks like your main power comes in on the side terminal. then low and high  on the switch side from your dimmer. The other side would go to your low and high beam terminals on the headlight itself. You could wire your fog lights to come on under either high or low beam but that may blow the fuse with the added current.

[desoto1939]

For your Foglights you only need a single headlight relay since this is no double filament.  The use of the relay is just to get more popwer to the lights.  A single will work just fine.

 

Rich Hartung

[Don Coatney]

  The use of the relay is just to get more popwer to the lights. 

Rich Hartung

 

 

A relay will not produce more power. The function of the relay is to remove the high amp load from the switching circuit

[greg g]

Let's look a bit closer at the the use of a relay as it concerns more power to an electrical load.  On a 6 V system where the efficiency of an electrically powered accessory depends on the amount of current reaching it, any device or circuit design that reduces the resistance in the path from the battery to the load will in effect in effect lessen the voltage drop from power source to accessory.  This will be more effective when the accessory is a high draw load like headlamps, horns and heater motors.  So placing a relay which takes it power fron the battery, as close to the load as possible can have a positive effect on the work of the load as the load will receive closer to its designed power and current, as opposed to running a wire from the battery through a wire, through a switch, then back out to the load, where the length of the run will incur inceased  resistance  through connections, within the switch ad at any terminals it passes through on the way to load. 

 

As noted, the relay transfers the high amperage load through a shorter and more direct path. leaving the switch circuit only to power the lower draw of the magnetic switches rather than the whole load.  Were it me, I would place the relay near where the terminal block is in the headlamp circuit.  the relay Rodney shows would then be powered by the wires coming forward from the stomp switch for the highbeams.  One to feed, the low beam side and the other for high beams.  The power to the relay would be a new line from the Battery side of the starter solenoid through a 10 gauge wire, to the power in of the relay. An inline fuse holder (30 amp) could also be placed in the line from the battery to the relay, although by the nature of the relay it should not be necessary. And while I was at it I would assure I have a clean and tight ground for each headlamp bucket.  This would take the place of the terminal strip as wires for both lamps low beam would be connected to the relay as would both high beams to the other out terminal.

 

It is easy to over think what is going on here which usually makes it more difficult to understand

Edited March 4, 2013 by greg g

[Guest bewillie]

I would place one side before the dimmer switch (which would be used for both high and low beam)then use the other side for your fog lights. 

[TodFitch]

I would place one side before the dimmer switch (which would be used for both high and low beam)then use the other side for your fog lights. 

The foot operated dimmer switch, at least on my car, is in a location where it can get a lot of spray when driving in the rain. As a result it may have corrosion and higher resistance than one would want.

 

I'd recommend putting the relay after the foot dimmer switch in the circuit to avoid that possibility of high resistance. Which means one side would be used for the high beams and the other for the low.

 

Modern cars, if equipped with fog lights, seem to have the fog lights only activated on the low beam. If the relay is not heavy enough duty to run both fog and low beams then a separate relay for the fog lights could be used.

[Don Coatney]

I would place one side before the dimmer switch (which would be used for both high and low beam)then use the other side for your fog lights. 

 

 

I agree. That would be the best way to do it.

[desoto1939]

A relay will not produce more power. The function of the relay is to remove the high amp load from the switching circuit

 Don yes you are correct. I could not think of the word to explain about the amperage issue.  Gregg has nailed the explanation very well.  Yes put the relay up onthe firewall or close the headlight  wireharness connectors and then run the 10 gage wire from the selinoid to the power side of the relay.  I have one on my 39 desoto and pickup the power supply directly off the started switch that sits on top of my starter. I have the pushrod pluner style starter mechanism and do not use a push button or or starter seliod like the later cars use.

 

Rodney should use the double rely for the headlight  and a single seperate relay for the fogs.

 

Rich Hartung

[desoto1939]

Also in the olden day it was illegal to run the headlights and the foglight at the sametime so some units have the headlight go off when the fogs are being used.  by state law.

 

Rich Hartung

[Alshere59]

Well since we are looking at it from all angles. Would the fog lights even require a relay? The switch is new, so not worn/corroded. Also I believe fog lights are standard sealed beams. With all new wiring and a relatively low draw why would a relay be necessary? Most put a relay in when they update to halogen (more draw) or just to bypass the resistance in the old worn headlight switch/wiring connections  anyway. Just wire it so it works when the key is on only so it won't draw down the battery if they are left on and your done.

One last comment.

The case of his current solenoid acts as a ground for the relay so he will need to make sure that has a good ground, so that may play into location.

 

Al

[greg g]

A relay should not be necessary for the fogs.  I do not run mine through a relay but do use 10 gauge wire all the way.  You are looking at 60 to 100 watts of draw depending on the bulbs you are using.   So at the high end you are using close to 17 amps.  A switch rated for 20 should be fine and cause no problems unless there are some iffy connections that add resistance to the circuit.  So again a minimal number of splices and junctions would in order.  I power mine from that ever popular battery side of the stater solenoid post, through a 20 amp inline fuse to the switch and then to the lamps.

 

While we are on the subject, I have also powered my brake light switch independent of the headlamp switch circuit.  Powered from guess where?

[Rodney Bullock]

I see, I did see a single relay he had for just the fog lights. I was just wondering I really don't know if the fog lights need it. On the subject of the headlights. I was told by him to use the battery terminal at the voltage reg. then use the juctions at the headlight terminals under the hood for the light connection. lastly he said that the switch terminal was to be connected at the light switch at the headlight position. Do you all think this set up would work? I think connecting it closest to the switch is the best idea. The dimmer switch in my car is hard to get to however if this is where it needs to be I will have to do it there.

[Alshere59]

Rodney

 

The battery terminal on the starter relay works fine. His advice to use the terminal block that is on the front of the car in my opinion is golden. You already have a slit/splice in the wires you just move the high and low beams off of the junction block onto the switched side of your relay. Then move the wires going to your headlights onto the other side. Why add another splice in the wires? I would redo the ring terminals to ensure a good connection but this is a very simple setup done this way. This is all you need and wouldn't have a reason to work on the dimmer switch or cut into any other wires at the switch's unless your wiring is bad. No reason to add work especially where it is hard to get at in the future and creates another point of failure from corrosion.

This comment "lastly he said that the switch terminal was to be connected at the light switch at the headlight position." I do not understand. Honestly if you go the way I outlined above you have working headlights already so I am going to ignore it.

Greg has outlined the fog light wiring well so I hope you have good luck and let us know how it worked out.

 

Al

[Rodney Bullock]

The light switch has 2 positions. The park light position and the headlight position.  On the relay there are 3 terminal connections battery, lights and the switch terminal. where would the "switch terminal be connected to?

[greg g]

Rodney. based on the picture that you posted you have a 5 terminal relay.  I am going to assume it is self grounding through the mount to the body or rad support. 

In the picture you are powering the battery terminal,  this should be the main power in ( Bat). 

The terminals that are opposite of one another are connected to main power by the magnetic coils. 

On these one side should be in (switch) the other side out (lamps). 

 

So you need to find the low beam wire from the stomp switch and connect it to one of the switch terminals,

then find the high beam lead from the stomp switch and connect it to the other one. 

 

 

Then connect the power out terminals to the two leads that go to the individual lamps for low beams, and connect them to one of the power out terminals,

 

locate and attach the two high beam lamp leads to the other power out terminal. 

 

Then connect the single side terminal to the battery, either from the battery directly, or from the terminal that the main negative battery cable is attached to.  That will make the relay hot whenever the headlamp switch is pulled to the headlamp position.

 

Assuming the self ground you should be set to go.  Check the system with your circuit tester, connect the alligator clip to ground, then touch the power out with the switch on and see if you get a light. if not cycle the stomp switch and see it it lights, the connect the lamps.  It doesn't matter to which terminal as long as both lows and both highs are connected to the same terminal.  And that terminal is powered when the dash indicator for highbeams is lit. The stomp switch will power them alternately regardless of what position is starts in, but you do want the highs on with the dash light.

 

Does this help???

Edited March 6, 2013 by greg g

[Alshere59]

Rodney

 

Depends on how you are trying to wire it.

 

If you are placing it between the headlight switch and dimmer switch.The switch side would be wired to the headlight postion in which case you would only use one side of the relay with the "lights" side going to your dimmer.

 

If you are wiring it after the dimmer then it would be hooked up as I said above.This keeps the fuses in line the way they are supposed to be.

 

Hope this helps and keep the magic smoke in as always.

 

Greg types faster I do believe.

[Rodney Bullock]

Happy days, got the headlight relay installed and the lights are "BRIGHT" thanks all. It's a great day. The wires were very easy once I inderstood that the like wires went with the like wires. White  and black with a power wire. thanks all

Edited March 9, 2013 by Rodney Bullock

[OldDad67]

I bought a relay about a year ago and have tried to install it many times. Today I think I am on the verge of the install. This relay is a dual head light relay. It has two terminals for the head lights which might mean I can run my fog lights thought it as well( Please chim in here if I am wrong) It has two fuses inside as well. It says it's Heavy duty on the case . I took a couple of picks for everyone to look at.headlight relay 004.JPGheadlight relay 001.JPGheadlight relay 007.JPGheadlight relay 009.JPG

I'm wondering where you guys live that you need fog lights that much, San Francisco? I hardly ever have fog here in the great Northwest and if I did I'd stay home or drive the wife's car. Just saying!

 

[Plymouthy Adams]

The Fog Lights are to some folks that items such as external visors, full dish trim rings, WWWs, fender skirts, clock, electric gas cap, cigarette lighter and radio are to others.....it's an accessory that defines the look of the era...who says it was needed???

[Niel Hoback]

We have fog lights for the same reason we have old cars; because we want them, not because we need them.

[martybose]

I'm wondering where you guys live that you need fog lights that much, San Francisco? I hardly ever have fog here in the great Northwest and if I did I'd stay home or drive the wife's car. Just saying!

 

Hah!  I live across the bay from San Francisco, have fog lights (on relays!) because the car had them when I bought it, and haven't ever needed them.  I did try to turn them on once, on a moonless night on a sharp twisty road, and managed to blow the main headlight fuse.  It turned out that the horn was against a lug on a barrier strip, just waiting for me to turn on the foglights! Fixed it years ago, still haven't turned the foglights on again.

 

Marty

[Rodney Bullock]

The headlight relay is really for the headlights. As the switch or what ever gets age on it the lights get real dim. The fog lights are more of a added feature. we really don't need them but boy do they look good!

[_shel_ny]

The headlight relay is really for the headlights. As the switch or what ever gets age on it the lights get real dim. The fog lights are more of a added feature. we really don't need them but boy do they look good!

 

And depending on which state you are located in.........to pass inspection ........... if they are there............ they must work........... and must be controlled independently from the headlights.