How do i wire aux driving lamps with a relay ?

Hi David,

First, check out danielsternlighting.com -- he has an excellent wiring diagram. Also check rallylights.com -- they might have one, too -- I don't remember. Regarding mounting the lights, check the 308 section -- there was recently a guy with a black 308 who made some brackets that fit to the bumper mount -- excellent, I think, because they require no drilling or otherwise permanent modification of any part of the car (plus, you have free range to aim the lights). (This was on a federal-spec car; I hope it works on UK/Europe bumpers, too.) I followed his example and am mounting Cibie series 35 lights on mine.

Second, read this: http://science.howstuffworks.com/question501.htm Comparing plumbing to wires is an excellent way to understand electricity, and why you can melt something by forcing a lot of current through skinny wires or contact points.

Anyway, yes, you absolutely need a relay. With the standard 55w H2 bulbs that Cibies use, you have a total of 110 watts; that will make a LOT of heat in skinny wires, and may melt the switch.

If you want some detailed instructions beyond that, PM me.


- Tony

 

You can go with or without a relay. The trick is that you run a heavy wire (#12-14) directly from the battery to each light. Make sure you have a fuse close to the battery and run the wire in a wire shield. Then connect the ground wires together and run 1 wire to a switch in the car. On the other side of the switch just run the wire to a ground. Now all you are doing is switching the ground which will turn on the lights. If you want to use the relay the only difference is you switch the relay on/off to power the lights. This would allow you to use a switch with a built in light which will let you know if the lights are on.

 

To power the lights using a SPST relay:
Note that lights, switch, relay coil and relay contacts each have 2 connections,
and there is no polarity or in or out. Use the 2 connections as is convenient.

One relay coil connect the switch. Other relay coil connection to fused battery.
The other switch connection to ground.
That's one circuit. Do it first, test by listening for relay clicks.
Use 18 gauge or larger wire for the wire from coil to the switch.

One light connection point to one relay contact connection.
Other light connect point to ground.
Other relay contact to the relay coil connection which also goes to fused battery.
Use 14 gauge or larger wire for this circuit if lamps or under 50W, 12 ga if over.

Fused battery means connect to the battery through a fuse.
To determine the size of the lamp fuse, divide the total lamp wattage by 15
for the current and add 50%. i.e. 50W lamp gets a 5A fuse.
Tidy neat wiring earns points.

The only thing you can do wrong is failing to make a good grounds.
Prep the ground point by scrapping and sanding to insuring you are
down to clean metal and use locking threads by lock washers or nylok nuts.
And no, you don't need a relay, if this were being adding to an American car
no one would consider a relay, but it's not...place the relay in a water safe
area between battery and the light.

 

http://www.rallylights.com/useful_info/auxiliary_lamp_wiring.htm

 

This is misleading. There is no "trick" that can substitute for a relay. The post implies that running a heavy wire directly to each light from the battery and putting the switch on the ground side of the lights solves the problem. Putting the switch on the ground side of the lights is no different that putting it on the hot side of the lights. The same amount of current is flowing on both sides of the lights.

If the combined current draw of the two lights is greater than the switch can handle, then you need a relay. There is no alternative way of wiring to get around this. Even if the switch can handle all the current I would still use a relay. Any time you can confine large current draws to short wiring runs at point of use by using a relay, do it. Bringing high current wiring runs into the cockpit increases risks for shorts and overheating of wires (yes I know it's fused) and adds voltage drop to the circuit, dimming the lights somewhat.

I also suggest you run the ground from the light circuit directly back to battery ground, and not to the chassis.

 

Hello David,
On the Euro spec cars there were special brackets that were mounted on to the bumper securing tubes that slide into the front of the chassis by means of a c type clamp and the lights were bolted to them.Maranellos still had some as I bought a pair last year but check the American bumper fixing first as I am not familiar with it so cannot say they will fit,but the parts dept staff are really friendly and helpful and will let you know without a doubt.
Regards, Tom