Last month, I added relays for my headlights. I hadn't actually driven in the dark yet, but I've had classic cars with stock wiring and I wanted to upgrade it . Also, the PO had installed halogen headlights already, so I didn't want any overheated wires in the future.

I found this site: WHY AND HOW TO UPGRADE YOUR HEADLAMP CIRCUIT used his diagram. I didn't want to just add relays and use the stock wiring, so I basically built my own harness using #12 wire. I also tied the lights all together with a common ground. I mounted the relays on the passenger side between the horn relay and the radiator

I cut into the stock wiring just behind the passenger side, outside light to get the 2 signals for the relays. Each relay send is on its own fuse (6 and 9).

Just like the diagram on the site, I used a separate 12v feed from the alternator, each having an inline fuse. So, since they are completely separate circuits all the way from the switch, one can go out and still have the other available. Since I used as common ground, I also added a 2 wire bullet connector for the inner high beams.

Here's some pics:

Completed Harness prior to install. The short bit on the left goes to the passenger side lights. It also has the 2 sends coming from the stock harness to the relay. the longer side goes across the front of the car to the driver side lights. Yellow are brights, Green are lows. Top Right is 12v source.


Mocked up Relays


Installed on Fender


High Beam Connector

 

Well done.

I did the same to the XJ-S, the S2 V12, and the S2 Daimler all in the Pre Computer days.

It just made sense at the time to remove all that amp load from tired old Lucas switches, and that NLA Hella clutching relay.

The improvement in available lighting on the road was huge. I could actually see where I was going.

 

Good job!

Many have reported good results by adding relays. I'm sure you'll be happy

Cheers
DD

 

Very nice job!
You'll really appreciate having multiple relays!

Soon after I came to this part of the world I had occasion to be driving the Feather River Canyon, well after dark, when my newly installed Halogens fused the shared High Beam relay and I couldn't dim. I finally had to open the hood and bash around blindly in the dark until I hit the relay and then the High Beams shut off. Needless to say, after that each High Beam got its own dedicated relay.

This coming Winter I want to do the same with Nix; upgrading to focus-beam Halogens and installing a line of relays (one for each light) across the top of the radiator mount, in deference to 40 year old Lucas wiring.
(';')

 

Relays have become fascinating to me. And one sojurn into them decades ago. Little understanding then, other than it was a good thing to do. I bought a well used back lot 37 Ford from the Ford dealer's
used car lot. It enjoyed a PO's installation of a sealed beam conversion kit. A loss in aesthetics, as the old elliptical glass lens gave way to a nacelle. Not too bad as to lighting. Better than old 32 CP bulbs and detiorated reflectors.


I think I found the head light relay kit in the J.C. Whitney catalog. School chum Roy, far more advanced in electronics as a Physics major at TWC helped me figure out the installation and contributed his skills with a soldering iron. As a school exercise and as a past time, he scratch built sound amplifiers.


Much better lighting on the old Ford. But, 6v has it's limitations. On one trip with a failing battery, I was forced to drive in lower gears to get more out of the generator!!!


Jump forward to the present.


I've contemplated added relays to improve volts at the lamps. But the logic of a circuitry escapes me. These posts intrigue me. And also, at the same time, puzzle me.


Is there a benefit in using the Hella relay as a trigger for other relays??


And, I barely understand that the Hella has a latching function which does what???


Kept in the schematics here??


Or, merely go back to eliminate the Hella and use the Light switch to trigger two or four relays. Oh, oh need the stalk to select "dim" bright and flash!!!


Or. way back when an eccentric EE on J-L posted his design of one relay as a "helper" to the Hella.


Added complications to thought process.


1. My Jaguar's lights as now constituted work very decently. Three
"newer" tech Halogens on three.


2. Stuff on the bench to move the outboards to 7" and new Halogens.
Include a rewire??? Add relays??


3. It works, leave it alone.....


Carl

 

Carl, don't think about the "circuitry". Think of it like water that runs from positive to negative. The relay is simply like the valve on an automated sprinkler system. It opens up when you send it a signal and allows the "water" to flow through. The 12v direct power is the "water". The wires I added were larger "pipes" that allow more "water" to flow through the headlights to the ground.

 

Carl,
I only added relays because I installed 100w Cibie Halogens as opposed the standard 55w incandescents.

If your 7 inch lights are of standard power incandescents you don't need any additional relays in your system because the system was designed for 7 inches to begin with.

As you say; If it works now, LEAVE IT ALONE!
(';')

 

Carl

The latching function is basically to switch to high bean and back again. High beam stalk is pulled and sends an earth pulse to the latching relay. Thats all it needs to switch to high beam and "latch" there with no ongoing earth required. Pull the stalk again and another pulse makes it latch the other way.

 

Thanks folks.


I do understand the function of a relay. Especialy the four pin variety.
A. The trigger circuit. One wire in and one out. Switch source in, out to ground.
B. The load circuit. Battery power in, wire out to load.


And, a variation, as using the ground leg as an additional control, as in neutral start.


Most of my puzzlement was why use the Hella relay to trigger other relays.


But, as Elinor says, my Halogens are not the 110w variety. Merely, the use of Halogen as the inert gas rather than an older version that uses a bromide, I think. Benefit. Halogen slows the detioration of the
reflector and deposits on the inside of the lens. More inert than the other, so to speak.


So, freshen, yes, redo, no!! As stated, they work!!!


Thanks again.


Carl

 

I think people are just a bit leary of messing with things upstream close to the headlight relay and cabin. If you move down stream to the headlights and add relays there:

a) you dont have to understand any of that stuff

b) you can position the relays close to the headlights, pump a good 12V+ to them and just have a short run to the lights themselves. Maximise the power with minimum messing about with the old wiring.

That's my theory anyway :-)

I went the other way as I wanted to unload the dash switch and get a less expensive generic relay for the headlight latching business.