sschevellecutlass_Bob

Decided to install headlight relay switches as the first step in my headlight upgrade. Did a few searches and came up with partial help..... can anyone please direct me to video or process (with pictures)? Particularly would like to make sure I pick the correct low beam and high beam wires in the wiring harness. Low = red/black and high = lt green/black?

Thanks

joe_padavano

It would help if you told us the year and model. Wire color codes changed over the years. In any case, this only makes sense if the relay is mounted as close to the headlights as possible. Run a heavy gage power wire (with maxi-fuse) directly from the battery to the relay. Use the old headlight wires to power the relay coil. Obviously you'll need two relays - one for low beam and one for high.

oldcutlass

Tis is one way of doing it, as Joe suggested use a maxi fuse in place of the fusible links. Run the lo beams in parrallel.

joe_padavano

I'll just add that if the OP is planning to upgrade the lights to something with a higher current draw (like HID lights). you'll need to upgrade the wire gauge from the relay to the headlights also.

sschevellecutlass_Bob

sorry for omitting car info..... 1970 Cutlass S. 350 Rocket. TH350 trans. Thanks for the info above!!! The overall endstate is either a set of the Brites, T3s, or Halogens. I'll upgrade the wire from relay to headlights! Thanks

joe_padavano

I don't know what "brites" are, but halogens don't really need the complexity of relays. Just be sure all the connections are clean and tight. Relays only serve to add potential failure modes.

As for color codes, just look at the back of he headlights. Green powers the high beam filaments and tan powers the low beam filaments.

Fun71

Agreed. My car has had halogen replacement bulbs since the 90s (80s maybe?) with the factory wiring and there haven't been any issues.

sschevellecutlass_Bob

The halogens sound good to me. Are you talking about a halogen sealed beam bulb? do you just get them from Napa or Autozone? Thanks

joe_padavano

I just get mine from RockAuto. They plug in and greatly increase light output.

sschevellecutlass_Bob

Awesome. Thanks Joe! Was stationed at HQ USMC years ago and lived in Northern VA. Great place!!!

oldcutlass

Yes, you can also get them at your local autoparts store including NAPA.

sschevellecutlass_Bob

ok ... picked up halogen headlights and relay parts........Stumped on where I splice the second relay????? It seems obvious that the first set of wires is in the front lamp harness running across the driver's side inner fender..(arrow in pic) ....but where is the second set? Do I splice the relay into the wires near the headlight? Thanks!

oldcutlass

As stated in the post with the drawing the lamps are in parallel, 1 relay for hi beams and one for low. I would try installing the lamps without the relays first.

Here is a better diagram



Your going to cut the 2 light wires, one side will connect to terminal 85, the other to 87 for respective hi or low beam relay and wire.

sschevellecutlass_Bob

I get it now!!! I drew it out on the wall board at work. Thanks for the patience and the second diagram. I'll try the healights first, but I do notice that when at idle the headlights dim a little then get brighter when I press on accelerator. Thought that meant a relay was necessary. ?

oldcutlass

Its normal for them to dim a little at idle. Make sure your battery is fully charged and the connections are clean and shiny. Make sure you alternator is putting out 14.5 ish volts.

sschevellecutlass_Bob

Installed the halogens today - super nice difference. based on above expert guidance, I tested the battery voltage at rest, and under load and since it was a constant 13, I just plugged in the headlights without installing the relay. steady 13 with the halogens too. So, i'll hold off on installing the relays at least for now. Halogens really make a great difference in visibility and confidence now. THANKS again all!

jeffsims

Guys,

I have been following this since I have been thinking about the relays too. My alternator is only putting about 13.5V. I measure 12.5V at the headlights.

Should my '67 442 alternator be putting out 14.5'ish. If so, then may I should start there. If I should expect 13V at the headlights, then maybe the relays not worth 0.5V.

-Jeff

joe_padavano

13.8V is about the right output, give or take. A one volt drop says you have dirty or corroded terminals. The relays are a bandaid - you're better off finding and cleaning the bad terminals, since this may also affect starting. In particular, I'd check the terminals on the threaded stud at the horn relay. I've had corrosion here that caused low voltage problems throughout the car. Also check the ground wires from the headlights to the core support. It isn't just the plus side that can cause problems.

jozw30

A lot of the automotive lamps are actually rated at 12.8VDC nominal. If you are getting 12.5VDC at the socket terminals, the relays really won’t do much unless you get a ton of voltage drop under load.

therobski

Joe, if you add headlight relays doesn't that take the load off the old headlight switch in the dash?

joe_padavano

Why do you think you need to take load off of a switch with contacts that were designed to carry that much current? Again, if you are replacing the stock lights with ones that draw a LOT more current, yes you need both relays and upgraded wiring. Otherwise, you are just adding complexity, cost, and potential failure modes.

oldcutlass

Yes, it takes the load off the headlight and the foot dimmer switch.

joe_padavano

Again, both designed to carry the current.

oldcutlass

I don't disagree Joe, only answered the question. My suggestion to the OP was to try his halogens first without the relays. People install relays and fuses everywhere for both perceived good and bad reasons. I use a Ford starter solenoid for my mini starter and a 30A relay to supply my HEI. I'm not one to judge.

therobski

My thought is it could extend the life of the old wiring and headlight switch. It cant hurt...

jozw30

The idea is to allow the headlights to get power directly from battery and not passing it through 50+ year old headlight & ignition switch contacts that have worn and corroded.

I believe the halogens are typically higher (rated) wattage/current than the old incandescent lamps were as well. Could be wrong.

Another thing to think about is that lamp output vs voltage/current is not linear. Much more dramatic losses right off the rated voltage than further down the curve.

I’d be more inclined to add the relays if you’re seeing lower voltage at the lamp contacts and further dimming under engine load. My 72 W30 has dim halogens that get worse under engine load. I’ll be adding the relays whenever I get time.

For sure it can’t hurt removing the current from the 50+ year old headlight switch. Have seen night and day differences (pun intended) in lamp performance with the relays added.

joe_padavano

If you are worried about this, put in a brand new switch and have 50 day old contacts.