Thread: Wierd Wiring for Driving LIghts

I'm finding it a little hard to follow your description, but the layout should be pretty straightforward.

The relay will have four terminals, or wires, depending on the relay. Two of those contacts will be the switch inside the relay, two will be for the electromagnet that drives the relay.

You're correct in saying that the relay switch terminals are taken up by "reasonably heavy duty cable from power source to relay contacts, other side of relay contacts has two cables that go to the light connectors, back from there to a common earth point."

The remaining two terminals are driving the electromagnet. One of those terminals needs to be connected to earth - pick any earthing point - indeed, many of these relays simply loop the earth wire through the mounting screw for the relay where you bolt it to the bulkhead. The remaining terminal on the relay needs to be driven by the switch. Power from hi-beams into one side of the switch, power out from the switch into the relay. That way your spots can only be activated when you have full beams on, and when you dip your lights, the spots turn off.

Hope that helps.

Here's what I've just said summed up in a diagram, and it's exactly the setup you are looking for.



The toggle switch is illuminated, thereforre there is a third wire from the switch that goes to ground. When power is going through the switch to the spots, the switch illuminates.

The only change I'd make to the illustrated circuit is that supply to the switch should come from somewhere along your existing hi-beam wire, because you want the spots to only come on when hi-beams are active.

Thanks Mike. I was going to take power from the high beam circuit straight to one side of the relay coil (because the relay is physically close to the headlights) and then take the other side of the coil to earth through the switch. That way I only need to run one wire from the relay to the switch, and then the second wire on the other side of the switch to any convenient ground near the switch. The fuse would go between the supply (high beam) and the relay.
But, if I do this I guess that negates the ability to have an illuminated switch, so I'll wire it as you suggest. I guess the wire to the switch need only be light grade, so even a thin twin-core would do the job and would be just as easy to route through the firewall as a single core cable.
For your info, here's the diagram I got with the kit. I would have preferred a proper circuit diagram, but I guess many people wouldn't know how to read it.
Spot Diag1.jpg

Cheers,

Coop

Originally Posted by C00P

Thanks Mike. I was going to take power from the high beam circuit straight to one side of the relay coil (because the relay is physically close to the headlights) and then take the other side of the coil to earth through the switch. That way I only need to run one wire from the relay to the switch, and then the second wire on the other side of the switch to any convenient ground near the switch. The fuse would go between the supply (high beam) and the relay.
But, if I do this I guess that negates the ability to have an illuminated switch, so I'll wire it as you suggest.

You could do it your way, and have an illuminated switch, you'd just have to run constant power to the switch connector that is usually earthed. Assuming that the switch you are using isn't illuminated by LED. Toggling the switch would ground the bulb in the switch at the same time as it would ground the relay.

However, as a general rule of thumb, any switch in an electrical circuit should be on the live feed, not the ground. Not as important in 12v applications I know, but good practice nonetheless.

Why don't you take the feed for the switch from the fuse box where the headlight feed is?? Or from the back of the headlight switch?? And then run your single wire out to from the switch to the relay to power it?? You don't have to run a wire all the way to the switch from the front of the vehicle where the headlights are...

Originally Posted by C00P

.
For your info, here's the diagram I got with the kit. I would have preferred a proper circuit diagram, but I guess many people wouldn't know how to read it.
Spot Diag1.jpg

Cheers,

Coop

It appears that the wire to which you refer is the earth wire from the coil of the relay - see Mike's drawing.

Originally Posted by mike_ie

Why don't you take the feed for the switch from the fuse box where the headlight feed is?? Or from the back of the headlight switch?? And then run your single wire out to from the switch to the relay to power it?? You don't have to run a wire all the way to the switch from the front of the vehicle where the headlights are...

Yeah, I know, it's just the thought of delving into the bird's nest behind the instrument panel fills me with horror every time I do it...

Coop

Originally Posted by p38arover

It appears that the wire to which you refer is the earth wire from the coil of the relay - see Mike's drawing.

Very likely the case, but that doesn't explain why the two terminals on the relay which operate it have three wires coming out of them. A twin core connected across the relay coil which goes back to the switch in the cockpit, and one shorter one with a ring terminal on it which, as you say, is probably the ground, connected to one of the terminals.
See this rough sketch of the layout (ignoring the wiring for the headlights themselves).
Relay.jpg
It's all a bit academic now as I'm not going to use the switch supplied, and I'll wire it the way Mike suggested. I was just intrigued by this wiring as I couldn't see how it would work. I guess I could put my multimeter across the switch wiring and see what gets connected to what as the switch operates. That might throw some light on the puzzle.

Coop

Originally Posted by C00P

Very likely the case, but that doesn't explain why the two terminals on the relay which operate it have three wires coming out of them. A twin core connected across the relay coil which goes back to the switch in the cockpit, and one shorter one with a ring terminal on it which, as you say, is probably the ground, connected to one of the terminals.
See this rough sketch of the layout (ignoring the wiring for the headlights themselves).
Relay.jpg
Coop

Never hurts to know these thing for future reference.

- The relay needs a ground line for the coil in order to work.

- The illuminated switch needs a ground line in order to work.

- The second line running between the relay and the switch is just a common ground line - saves you from having to ground the switch behind the dash, where you might be caught for space, or dealing with more plastic than metal.

To make it clearer, this is what the inside of your illuminated switch looks like, and how it works: