Relays for headlights

[Russell Ashley]

This has been discussed more than once before, and I was always of the opinion that a relay wasn't needed when running halogen head lights. I've run halogens in every vehicle that I have owned for as long as I can remember with no problems, that is until now. I have a new headlight switch from Danchuk, and halogen sealed beams in my TF. Last night I was coming home from a cruise in about 25 miles from home with the dim lights on. It was fine on dims but when I switched to brights it only took a minute for the lights to start going on and off. I turned the lights off for a few seconds to let the bi-metal strip on the switch cool down, and then turned them back on on dim and drove home with no more problems. I'm only throwing this out because I think I have commented before that I didn't think a relay was necessary, but apparently the switch in a TF isn't capable of powering Halogens reliably. It could be just my switch but it is new.

[OrrieG]

I added headlight relays (and others too for other high load stuff) when I rewired mine. I had a couple of close calls with the stock wiring and wanted the peace of mind. Plus I plan on upgrading to more modern lamps in the future.

[JonnyC10]

I installed a relay harness and Hella Vision Plus H4 conversion a couple days ago. Havent got a chance to try it out yet since my truck is halfway through the CPP Big Slam kit install.

[mr48chev]

Installing relays is simple and inexpensive and keeps your switch (s) from overloading or burning out.

On my 71 GMC I was going through dimmer switches about every three or four months with 55/100 H-4 bulbs. After putting a pair of relays in no more problems. I put an inline fuse in the power feed to the relays.
Around here you need all the light you can get at 03:45 in the morning on the way work as there are quite often drunks staggering up the side of the road and sometimes in the road usually wearing all dark clothing.

[poncho_villa]

Originally Posted by mr48chev

Installing relays is simple and inexpensive and keeps your switch (s) from overloading or burning out.

Can anyone post a schematic on how to wire in relays? Also are two required for low and another two for high beams? Many of us can rebuild a tranny or a carb blindfolded but are lost when it comes to wiring.

[OrrieG]

Will when I get to my computer..

[Rude Dude]

This site has schematics for dual lights

http://www.rowand.net/Shop/Tech/imag...ingDiagram.jpg

[VTX-Black]

I had the same problem on our 84 with headlight flashing on and off.
I found a kit that had a sub harness and relays that plugged in to the existing connections.

I got it from LMC. It was cheap and took me about 10 minutes to do.
If they don;t have one for our old trucks, I would buy the one for an 84. It wasn't much more than sourcing the components myself.

[Russell Ashley]

I already had the relay when I rewired my truck using an EZWire kit. I've just never needed a relay with halogens before so I elected to skip the few extra steps and leave it out. To keep it simple but still functional I will stick with only one relay that will be in the feed to the dimmer switch. The wire from the light switch that formerly fed the headlights will only be used to pick the relay. I have new wiring so I don't think I will have any noticeable voltage drop to the headlights with this configuration. The feed to the dimmer switch will connect to a full voltage point and will definitely be fused.

[OrrieG]

That will work too, keeps the big load off the switch. I think the EZ wire size from the dimmer switch is larger than the stock 20 ga. too, but would have to look to comfirm, to allow for newer higher amp draw lights.

[_Ogre]

ezwire has an auto reset breaker in place of the headlight fuse, but chances are that is not your problem
the bimetal switch is what is causing the headlights to flash
reach up under the dash with a pair of needle nose pliers and bend a little more contact in the bimetal strip
you will still be protected by the breaker in the ezwire harness and that is protection for the headlight circuit
you could also solder the points closed as your still protected with the breaker
no relays needed

[1project2many]

I'm only throwing this out because I think I have commented before that I didn't think a relay was necessary, but apparently the switch in a TF isn't capable of powering Halogens reliably. It could be just my switch but it is new.

Even when the switch can conduct enough current to keep the lights lit, the OEM wiring has enough internal resistance to significantly reduce brightness. Headlight harness "upgrade" kits were popular for several models of car in the '90s and early into this century which were essentially relays mounted near the headlights and battery power supplied through larger wiring. On a standard 65W halogen high beam, 6' of 16G wire at 14V adds enough resistance to the circuit to equal 2 watts lost. The difference in intensity is noticeable.

[solidaxel]

Here is what I have on my square truck.
My neighbor has them on flebay (sunset fabrication), they only require a new 12ga feed from a battery source and a ground

[Russell Ashley]

I wired mine as I mentioned before, using only one relay. I haven't measured the voltage at the headlights to see if there is a noticeable drop but the lights seem bright to me and don't go off so I'm happy. I have all new wiring so I wouldn't expect to see much voltage drop at the lights. You can always take it a step farther by using multiple relays but the single relay like I did would probably be sufficient for most of us.

[Russell Ashley]

My last comment on this: If you want to use the one relay method you can do it all right at the light switch. I mounted my relay to the top of the kick panel. It's the easiest way to do it and there are no extra wires needed other than the wires from the switch to the relay, and it isn't visible under the hood.

[Russell Ashley]

I said I wasn't going to comment on this any more but I need to correct one of Mr48's points. The light switch is no longer in the circuit to the head lights when you use the relay so there's no voltage drop there. The switch just picks the relay which is connected to battery voltage. I'm using off the shelf Sylvania halogens, not aircraft landing lights, and I do have all new wiring. It works fine and my lights are bright, and most importantly they stay on since the bi-metal strip on the light switch is no longer in the circuit.

Use as many relays as you like. I was just suggesting a cheap easy alternative to the multiple relay setup. I also like the fact that my relay is inside the cab under the dash so there is no visible wiring changes.