Headlight relays: cheap, one afternoon project with big payoff

[johnbendik]

I am posting this to encourage anyone who has not added relays to their headlight circuits to do so.  It's a quick, fun project that makes a huge difference in your headlight brightness.

When I first got my Eagle, I was dismayed to see how dim and 'yellowy' the headlights were.  It was so bad that I hesitated to drive it much at night.  At first, I blamed the old-school small rectangular headlights.  I replaced them all with halogen units, and they actually seemed a little worse.  Then I did some research on this board and elsewhere, and learned that AMC did not use relays for the headlights (in 1984, at least); the entire current for all 4 headlights runs all the way from the battery to the headlight switch on the dash and back to the lights themselves!  I looked at the wire on the headlight side, and it was very thin gauge, I'm guessing 18-gauge at best.  I wish now that I had actually measured the voltage drop at the headlights themselves (for a before/after comparison), but instead I jumped right into the relay project.

I used this article as a guide for the project:  http://www.danielsternlighting.com/tech/relays/relays.html     Although it is not Eagle-specific, it explains the benefits of adding relays to older cars very well, and has lots of how-to information.

I bought a couple of relays (Metra Install E-123 Bay Tyco Relay 12 Volt 30 Amp, $6.45 each on Amazon), a spool each of red and black 14-gauge wire, and a inline fuse block (In-line ACT Water-resistant Fuse Holder - 10AWG, $3.05 on Amazon).  If you buy some other relay type, make sure you get the kind that have two output terminals, so you can run a separate line for each headlight.  I started out wanting to use sockets for the relays themselves, but all of the ones I could find used thin 16 or 18 gauge wire for the leads, which would have defeated my purpose.  So I ended up going with regular 1/4 inch female terminal connectors, which I soldered directly onto the wires to the switch and lights.

To keep all of the wires as short as possible, I mounted the relays on a wooden block very close to the battery.  I grounded the relays and all four headlights (14-gauge black wires) to one of the mounting screws for the small metal thing (relay?) mounted right behind the battery.  I used individual wires for power to each headlight (14-gauge red wires), running directly to the relays.  Here's a picture, looking over the fender from the passenger-side corner into the engine compartment:


The thick red wire loop is the 10-gauge positive feed (with 40-amp fuse) for the whole system

The difference this made was amazing, literally like night and day.  The 'yellowness' is gone, and the lights are much, much brighter.  And I have to think it's a little safer to not have the full lighting current running up to the headlight switch on the dash.

John Bendiksen

[vangremlin]

Thanks for the write-up!

[carnuck]

Mine are being set up so that a high beam and low beam for each side is on one relay. That way if one relay blows I still have light on the other side.

[johnbendik]

I don't see how that could work unless you have 4 relays. A single relay is activated by a 'signal' from the headlight switch, which can either be a 'low beam signal' (switch is in low beam position) or a 'high beam signal' (switch is in high beam position').  If both high and low beam for a side are hooked up to one relay, then both beams are going to come on when that relay is 'signaled'.  Maybe I'm missing something...

Now if I substitute the word 'fuse' for 'relay' in your statement, it makes perfect sense.  I thought about using separate fuses for each light, or separate fuses for low and high beams, which would give the flexibility you describe, but decided it wasn't wasn't worth the extra work.  For me at least...

John Bendiksen

[HornetRWB]

I think the 40 amp fuse is too big (relay will die before the fuse blows) and I agree that it should be split into separate fuses for highs and lows. Much safer that way (try doing highway speeds at night and your lights go out...).

[carnuck]

The relays I use were designed for hi/low or similar. They are 3 position. On, normally Off and the other On. The high beam switch can feed ground or power to the relay to engage it. I'll have to look for the number again. There is even one lighting relay I got from a Toyota long ago that also had the parking lights in it. I remember that one so well because I kept chasing light outages around the car and finally found the relay in th factory position under the hood with the wires upwards and full of water! I believe it was a '78 Corolla or Crown.

[johnbendik]

HornetRWB, I had to use the 40 amp; a 30 amp worked fine with just low beams but would blow when I switched to high beams (all 4 bulbs on).  I wouldn't mind so much if I blew a relay since they're so cheap;  I was mostly interested in protecting against a wiring-induced fire.

All that being said, you're still right that it would be better to fuse the two circuits separately.  Then I could use fuses that were less amps than the 30-amp relays, thereby protecting them too.  I'll be getting around to that eventually.

"(try doing highway speeds at night and your lights go out...)"  Actually, my skills for dealing with that scenario are pretty finely tuned.  My first several cars (in the 70s) were old British sports cars (Triumphs, MGs), all of which had Lucas 'Prince of Darkness' electrical systems.  And I was living in Galveston, driving to Houston to work the night shift (50 miles away) at the time.  So I had lots of 'character building' (and pants-soiling) experiences during that time...

JB

[eaglefreek]

Relays and the right bulbs make a big difference. If you have a U pull it junkyard near you, I prefer the water proof Bosch relays found in many 90's GM vehicles. I pay only $2.50 for the relay and pigtail.

[johnbendik]

Eaglefreek, that is a very slick looking setup.  I especially like the mounting rack for the relays.

Incidentally, for anyone thinking about tackling this project, the relays I listed in the original post are also waterproof.

JB

[eaglefreek]

Eaglefreek, that is a very slick looking setup.  I especially like the mounting rack for the relays.

Incidentally, for anyone thinking about tackling this project, the relays I listed in the original post are also waterproof.

JB

Thanks, I think the mount is from a S10. Not trying to be critical, but while the relays may be waterproof, the connections aren't. They may allow corrosion, not to mention the exposed power wires. There are connectors available for those relays if you want to protect the connections http://m.ebay.com/itm/251644220337 I had relays wired like yours for a. few years without any issues, just making you aware of options.

[IowaEagle]

Thanks John.  I will put this in the Eaglepedia.

[rmick]

Amazon has this. http://www.amazon.com/gp/product/B00C0SATHE/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

[johnbendik]

rmick,

That's a great 'bundled' price.  But be aware that the relay sockets in the package are probably crap... they appear to be the same ones I bought for my project (http://www.amazon.com/gp/product/B005EUWMU2/ref=oh_aui_search_detailpage?ie=UTF8&psc=1), and I ended up not using them because all 5 wires were 18 gauge, as opposed to what is advertised (18 gauge for the control wires and 14 gauge for the load wires).  They made the load wires appear bigger by making the insulation thicker, but the actual conductor is the same thickness.  Several of the Amazon reviews make the same observation.

I can't comment on the quality of the relays, but given that they misrepresent the quality of the sockets, I would be a little leery of them.

JB

[MortenB]

I installed a similar setup in my SX/4 with dual fuses and relays.  That way I can still have lights if one fuse or relay fails.  I also added a diode between the relays to allow the low lights to remain on with the brights.  That way I have 6 lights on high beams.   Huge difference over the stock setup.   Instead of a diode, one can use a 3rd relay to do the same thing.  You need the brights feed to also activate the lows, but not have the low feed activate the brights.

[eaglefreek]

I installed a similar setup in my SX/4 with dual fuses and relays.  That way I can still have lights if one fuse or relay fails.  I also added a diode between the relays to allow the low lights to remain on with the brights.  That way I have 6 lights on high beams.   Huge difference over the stock setup.   Instead of a diode, one can use a 3rd relay to do the same thing.  You need the brights feed to also activate the lows, but not have the low feed activate the brights.

I thought about doing that, but is having both filaments powered too much heat for the bulb to handle?