Headlight relays

Anyone here added relays to their headlights?
I have also posted this question over on the fordforums, but I know some of you guys must have done this.

I looking at this and wondering where to tap in to the red/b and green/b wires in the harness. You've got a separate run from each light going in behind the firewall. I want to know how those wires connect up with each other and into the switch. I'm assuming I would have to splice in "upstream" from wherever those two sides meet?

I have single lights on my '78.

I don't need another wiring diagram, thanks, just want to know where, physically, to make the connections.

I also seem to remember reading about one fellow saying he tapped out of the headlight socket, and didn't have to cut any wires. How does that work?

HandyAndy wrote:

I also seem to remember reading about one fellow saying he tapped out of the headlight socket, and didn't have to cut any wires. How does that work?

That's what I'd do if it were me. It seems the most simple. Just get yourself some spade terminals that are the right size to slide in there, and stick one in the low beam hole, and one in the high beam hole. Run your wires to the coil terminal on two relays, one for high beams, and one for low. From the other coil terminal on the relays, go to ground.

The other side of each circuit is even easier. From the battery, through a protective device (I'd try to find a self-resetting circuit breaker...nothing worse than losing lights, although, with this setup, if you blew one fuse, you could just switch to the other beam), to the switch terminal on the relay. From the other switch terminal to the lug for the beam you're working with, and from the ground lug to ground.

Done, and done.

Hope this helps.

Later,
Mike.

tapping into the headlight socket would be effective, but the reliability issue could be compromised by the weather and vibration.
it would be a better idea to solder all connections and use a protective heatshrink tubing/sleeve for weatherproofing. it sounds like a pain in the ass, but for peace of mind its worth it.
just for general info most relays are wired as:

30 fused power
86 (relay coil) switching/trigger
85 (relay coil) ground
87 power to component
87a not used
terminals 86 & 85 can be reversed in most cases unless a diode is used in a prefabricated hardshell connector. if you are wiring the relay direct to the wires, it makes no difference as 86 & 85 are just a magnetic switch witch connect terminals 30 & 87.

the beauty about using relays is that they can be reversed. meaning that you can supply power to the component in a "hot at all times" circuit and use the relay to provide a ground circuit to the component. this is the method i prefer. it would be wired as:

86 (relay coil) switching trigger
85 Relay coil) ground
30 body ground
87 Ground to component
87a not used

never substitue a smaller gauge wire when running a power supply or ground to a component.

the relay coil wires can be 16 guage or smaller depending on the lenght of the wires as the relay coil has a low power consumption.

relays can be "ganged" to supply heavy current for components

what are you trying to do?

no disrespect meant to AUG

Thanks, I appreciate the discussion.

I see the advantage of tapping into the headlight socket in that you can replace the existing wiring with a heavier guage rather than run power through the original.
But it is a more exposed connection, so maybe just cut off the one socket and use proper connectors. You can use the socket for the light anyways...

What is the advantage to using the hot at all times method?

most manufacurers are using ground side switching nowadays. the best avantage of using gound side switching is that it reduces the arcing on the contacts of relays and switches, making then last longer. it can make diagnosing easier also.

fangar150-ex wrote:

most manufacurers are using ground side switching nowadays. the best avantage of using gound side switching is that it reduces the arcing on the contacts of relays and switches, making then last longer. it can make diagnosing easier also.

To elaborate on ground side switching and how it reduces arcing...

Every load in an electrical system causes a voltage drop accross the component, so if you put the switch in the system after all of the components, then the voltage that the switch sees is at its lowest point. Of course, less voltage causes less arcing.

No offense taken, man. Just because a thought is mine, doesn't necessarily make it the best, or even right for that matter. Hell, now that you mention it, I may even have to switch some stuff around on my fan control circuit...maybe when I add the extra fan.

Yup, thanks for the input guys, I'll have to look at this method as well when I get to it.

I just finished painting my engine bay, and am getting ready to reinstall the engine and all the other doodads this week. Going to try to get this mod in just after I get the engine going.

thats the good thing about about about a forum, theres always more than one idea out there, id have never thought about using 2 fans for the condensor and radiator if aug didnt mention it.
i have started to experiment with using "buss" wire set-up off of the starter relay under the hood for things like efi , fuel pump amp, etc. the idea isnt new, because back in the day ford used the starter relay as a "buss" point for all power under the hood and into the car.when i was starting to add a 130 amp alternator,i thought it was obviously better to use the alternator fuse as a buss point. it just saves a lot of chopping into the loom, this should be usefull especially around the ignition switch area.
at least you guys finish your cars and drive them, while im making changes to changes that have already been changed, wasting more time and drilling more holes.
now i want cold air intake. (after i patch-up the big hole i cut into the apron to add the lincoln mkvii air filter housing) later jb....

That's why I took 3 years to do a one year job...I kept thinking and thinking, and changing things in my mind, so that I wouldn't have to go and do them twice, becasue I wanted to think up the best way to do it first.

Of course, right after I hooked up all of the wiring to the front of the engine, from the driver's side, along the stock routing, with the wires the *perfect* length, my buddy comes up and says, you should've put a clamp right here (points to the power steering bracket), and run it there. I said, "Where were you two f#@&ing days ago?!? Now shut the f@$* up and go away!" Of course, the wires weren't long enough to take his suggestion, or I probably would've.

Then there's you with the reminding me of ground side switching. That one's worth changing stuff for, but not on the highest priority

Later,
Mike.