Headlight Relays Redux

[ZOA NOM]

I've taken the plunge, and I think I have what I want.

I started with a drawing:




and ended up with this:




There are six SPDT relays, two for each headlight and one each for the driving lights. I can use the driving lights with parking lights, and they will come on with highs and flasher. Installing today, with stock bulbs.

[vash]

good god, i will NEVER post the picture of my homemade unit. it involves some use of zip ties.

[ZOA NOM]

Zip ties are cool, Cliff. They're holding the relays together, see? And yes, that's duct tape for labels!

[ZOA NOM]

A closer look:

[ianc]

Wow, six relays. I thought about four when I did the H4 conversion in my SC, but ultimately went with just two, one for high beams and one for low beams. I guess you get less catastrophic results if one of them goes out with 4 headlight relays, but there is more there to break though...

ianc

[vash]

wow, rick. your zip ties look good. mine are more of an afterthought. that is a slick system. you should come up with a cost and sell a few. i dont even have high/low separated in mine.

[ZOA NOM]

ianc, actually, I am using only one relay to drive each headlight. I am using both outputs of one relay, one for high, and the normally closed one for lows. That way, I only need one fuse for the headlight. The relay feeding it simply turns it on or off. The only drawback is that the battery supply has to travel through two sets of contacts, but it wasn't much of a compromise for having the flexibility I wanted.

[ianc]

OK, I see what you're doing. But what is the advantage of using those two additional relays that are activated by pulling the light switch knob out (top left pair)?

Here's how I did mine:



ianc

[Wil Ferch]

Those connectors are "Posi-Seals" and "Posi-Locks"....right?

I posted on these where soldering is impractical or you want dis-assembly possibility....

Wil

[ZOA NOM]

Yes, but I might swap them for the "sealed" ones. These don't seem to seal on the ends. I do like the way they work, though. There is a "bullet" inside with cones on each end, and the wires splay around them when you screw the cap on. It's a very tight connection.

[ZOA NOM]

Originally posted by ianc
OK, I see what you're doing. But what is the advantage of using those two additional relays that are activated by pulling the light switch knob out (top left pair)?

Here's how I did mine:



ianc

The advantage is that the current is only flowing through one headlight. With only two relays, current from both headlights will flow through one. If a relay fails, I will still have one headlight working.

[ianc]

The advantage is that the current is only flowing through one headlight. With only two relays, current from both headlights will flow through one. If a relay fails, I will still have one headlight working.

True in a way... If I lose one relay, I will lose either highs or lows in both beams, but both headlights will still work on the non-failed relay. If you lose one relay, you'll lose both high and low on one beam. If I'm coming back from the bar with a couple beers under my belt, I think I'd rather have both beams working if one relay fails.

I still don't see what using the left upper set of relays buys you though except a voltage drop and a couple extra points of failure...

ianc

[ZOA NOM]

Basically, the upper left set feed the low beam voltage to the upper right set when the headlight switch is on. Without them, I would have no independent HI/LO operation. Also, there is theoretically no voltage drop across a closed set of contacts.

It seems we have both come up with usable ways to accomplish a goal. My goal was to avoid running the current from two filaments through one relay in parallel, which doubles the current. If a relay fails, it will most likely fail closed in the low beam (normally closed) configuration. Unless you wired your lights in series, your relay will be carrying twice the current mine will. Who's is more likely to fail?

[71T Targa]

Are you going to be building and selling these? It looks great!

[ZOA NOM]

No, it was more of a project than I would care to repeat very many times. I'll be happy to provide the parts list and wiring diagram to whoever wants it, though. I got the relays from JC Whitney for about $6 each, and then miscellaneous wire and connectors, etc. from Orchard Supply. Total was under $100

[ianc]

If a relay fails, it will most likely fail closed in the low beam (normally closed) configuration.

Ah, that is a very good point. I hadn't thought of that.

ianc

[ZOA NOM]

In reality, it's probably overkill, but I like that each circuit is isolated, for troubleshooting, and repair. I also won't worry much about high wattage bulbs.

[ZOA NOM]

Yowza! Just finished the install. Had fun with the alarm not shutting off. It seems the alarm has a feed from the bottom of the fog light fuse (#21, closest to the front of the car). With that fuse removed, the alarm doesn't shut off! I had to put the fuse back, and get the switched 12v from pin 86 on the fog relay. All better now.

[ZOA NOM]

OK, small change to the drawing.





In the upper left corner, the connection to the headlight switch must be made under the dash, on the actual switch. I thought I could get the switched voltage at the fuse panel, but by the time it arrives at the fuse panel, it is split up as "Low Beam & High Beam". This results in the control voltage disappearing from the first set of relays when High Beam is selected. To keep the first (upper left) set of relays energized when Hi Beam is selected, you have to get the switched voltage from the switch. Luckily, it's a very easy tap. The lug for pin 56 on the switch happens to be on the bottom of the switch (white with black stripe) right under the dash. Fish the wire into the trunk and clamp it down on top of fuse #3.

[Mysterytrain]

I wired mine with the two relay set up. Cibie with 90/100watt bulbs. I was also able to find a nice little fuse block to protect everything. I'm very happy with the upgrade.