A Different Headlight Relay Upgrade - 4 Relays

[Captain Obvious]

I recently completed a headlight relay upgrade, but I did it differently than the traditional approach. It's a little more complicated, but I think the results were worth the effort. Basically, I used four relays instead of two so that each filament has it's own set of contacts and high currents are not shared on the same set of contacts. While I was at it, I also modified the headlight switch to connect to ground instead of connecting to power. This enabled me to reduce the number of wires needed run to the relay block.

 

Advantages are:

Uses the original fuses in the fuse block and does not require additional wires run from the battery.

Original fuse block lid printing still accurate. Original fusible link still accurate as well.

Independent failure modes. One blown fuse or relay fault won't turn out all the lights at the same time.

Each filament has it's own relay minimizing losses in the relay contacts. High beam currents are not shared.

Fewest number of wires going to the relay block (six).

 

Disadvantages are:

More complicated than the traditional approach. Not plug-n-play.

Have to modify headlight switch and jumper around headlight switch under steering column. (Much easier than it sounds!)

Have to run additional R/B wire out to one of the headlights.

 

Here's a schematic of how my headlights are now connected:

I took some current and voltage readings before and after the upgrade and I'll get them into presentable form and post the numbers. The results were illuminating.

 

[siteunseen]

Your topic is very enlightening. ​  

[Captain Obvious]

Thanks for the glowing review.

 

I've got a couple other sketches of different alternatives, each of differing levels of complexity and advantages/disadvantages. For example, a compromise on the 4-relay version above is one that uses two relays instead of four. This two relay version is simpler and would probably be what I consider the "sweet spot" between complexity and benefit.

 

Advantages are:
Uses the original fuses in the fuse block and does not require additional wires run from the battery.
Original fuse block lid printing still accurate. Original fusible link still accurate as well.
Fewest number of wires going to the relay block (six).

Somewhat independent failure modes. One blown fuse or relay fault won't disable all the beams at the same time.

Disadvantages are:
More complicated than the traditional approach. Not plug-n-play.
Have to modify headlight switch and jumper around headlight switch under steering column. (Much easier than it sounds!)

Filament currents go through the same relay. High beams will pull almost 10A through one set of relay contacts.

I really like the fact the original fuses are still used and fusible link rating is still appropriate. I also like that there is more than just one fuse for the whole headlight system as compared with the traditional approach.

 

And other than the changes required to the headlight switch (which sound more terrifying than it really is), this version can be done with add-on harnesses which can be removed at a future date if desired. That's why I'm thinking this may be the sweet-spot between features and ease of use.

 

When I did my 4-relay install, I had my harness ripped apart because I was also changing for the internally regulated alternator and a starter relay. Because I was in there for a couple different things I went whole hog on the 4-relay version. I figured I was in there anyway, I may as well do the best I can since I wouldn't have an opportunity like that again.

[siteunseen]

You are such a bright guy, can't wait to shake your hand.

[Captain Obvious]

So for the two versions above, one of the changes you have to make is to short around the original headlight OFF/ON switch in order to make the original fuses hot at all times. Sounds more complicated than it really is...

 

Under the steering column, just disconnect the bullet connectors on the big W/R and RED wires from the headlight switch and then plug them together instead:

 

Now the headlight fuses are hot at all times.
 

[rossiz]

wait a minute... you mean i gotta take out ALL 5 of those little screws that hold the clamshell together, unplug BOTH wires and then plug 2 of em back together?!? i need a beer after just thinking about that!

 

 

seriously, great work and we all benefit. thanks for sharing the brilliance - you are a true luminary.

[Captain Obvious]

Might depend on the year, but it could be more complicated than you make it sound. There are actually has SIX  screws holding my clamshell in place. 

 

 

 

 

[Captain Obvious]

Now that we have fuses that are hot at all times, let me shed a little light on how I modified the headlight switch to connect to ground instead of +12. 

 

First, de-solder the two original large wires from the headlight switch. Note the two shiny empty connections on the right side:

 

Solder on a couple smaller wires with bullet connectors on the ends. One male, and one female. Doesn't matter which one goes to which post on the switch. Snap the male bullet into the large dual bullet black ground connector and leave the female hanging:

 

Plug the male bullet from the HI/LO beam selector stalk into the female bullet and you're done. Note that the wire from the HI/LO selector used to get plugged into the large dual bullet connector on the black wire. Now instead it goes to the female bullet to the headlight OFF/ON switch:

 

So now, with the headlight switch OFF, the HI/LO switch doesn't connect to ground, but with the headlight switch ON, it grounds the beam selector switch.

 

While I was in there, I also took apart my headlight/parking light switch and cleaned up the contacts, but since there are lots of other threads detailing that portion, I probably don't need to go into details here. Here's a pic though, just because. This is before I cleaned up the contact:

 

 

[tamo3]

I was comparing your schematic and Jim's schematic which one is easier to deploy...

http://www.classiczcars.com/topic/50416-75-280z-headlight-relay-upgrade/?p=458629

 

 

I was wondering where is your dimmer switch?

[Captain Obvious]

My dimmer switch (I called it the HI/LO Beam Select) is in the lower right of my schematic.

 

As for the deployment difficulty, I'm not sure which would be easier. Assuming the new plug-in harness construction is the same difficulty for either version, that part is a tie. Then for the traditional approach you have to run a new power wire and fuse from the battery, while for what I did you have to make a couple changes to the headlight switch instead.

 

All things considered, I think the traditional approach is a little easier, but I think the benefits to what I did were worth the small extra amount of work.

 

I'll try to draw up another schematic of my modified 2-relay version that shows more clearly how to construct a harness.

[Captain Obvious]

Here's some info on the relays I used for my headlight upgrade. The relays themselves are used in lots of applications and are easy to find, but what really grabbed me about these isn't the relay at all... It's the socket.

 

This relay/socket combo is used in lots of Hondas and Acuras (For example, All 98-00 Civics have at least one assy and two if it has a sunroof). They come in SPST and SPDT applications depending on the original use (for example, horns use SPST and sunroofs use a pair of SPDT). They are easy to harvest and can be found under the left side dash near the driver's left knee. Some models only have one position populated, but have a socket that will accept two relays. Depends on whether it's a manual or auto. And cars with a sunroof will have a second socket (with SPDT relays).

Here's the socket and relay combo I used. It's small, comes with a mounting bracket, and accepts two relays:

 

Remove the relays and you're looking at this:

 

What I found really useful about these sockets is if you strip down two of them like this:

 

They gang together!!! So if you need more than two relays and want to mount them all in the same place:

 

Put in four relays and you got this. It's much more compact than the "Bosch style" relays:

 

Since I had just completed an internally regulated alternator as well, I put my headlight relays in the spot vacated by my original external voltage regulator:

 

On the last pic, you can see the retaining feature on the end that makes them gang-able. It really helped simplify the mounting and kept the size as compact as possible.

 

[TomoHawk]

Here's a wrench for your idea:  Can you figure out how to do this with less wires through the firewall?  You're trying to put 4 more wires through a large grommet that is packed full of wires already (on my 280Z for example.)  You may split the grommet and lose the seal if you force too many new wires through there.

Edited June 3, 2015 by TomoHawk