I had a private message that asked me about relays, so thought I'd post here for the benefit of anyone who searches for it. 
The last time I fitted relays to headlights was years ago and I can't find the photos - except one (below) that shows the result - one of these headlights has the relay fitted, and the other uses the standard wiring.
I shall turn this thread into a guide - with pictures - when I next carry out this modification. In the meantime...
What is a relay?
A relay is an electrically-operated switch (the Italian term, Teleruttori, is a little more emotive, rather than the English that means a torch-passing race). There is a coil of wire inside the relay that forms an electromagnet. The switch contacts move (they are influenced by the magnetic field) when a current flows through the relay coil.
There are usually at least four terminals on a relay:
- two terminals (numbered 85 and 86) provide the power to the relay coil
- one terminal (30) has power connected to it. This is the moving contact.
- one terminal (87) is the other (stationary) contact. This becomes live when the relay turns 'on'.
- sometimes, there is another terminal, often numbered 87a. This may either become live at the same time as terminal 87, OR it may be live when the relay is off and become 'dead' when the relay turns on. This latter possibility is known as a 'changeover' or 'cutout' relay, useful for reversing the direction of a motor (e.g. electric windows https://www.fiatforum.com/uno-technical/81347-electric-windows.html?p=899346) or turning something off when something else goes on.)
The picture below shows a standard relay. Usually these are black but they can also be grey, green, red, blue, white, etc. The colour doesn't reliably indicate the type or function.
Sometimes, the relay is a taller or wider shape and has extra electronics inside to turn the relay on when there is a special signal on extra terminals, or after a certain length of time. Examples include fuel pump relays, central locking control relays, interior light delay relays, and others. You could say that the additional electronics make each of these 'relays' actually a 'relay plus control circuit', but people still think of them as relays (and get confused). Just think of them as 'control units' instead The rest of this article talks about only the standard relay.
Why use a relay?
The relay contacts can carry a large current - up to 30A for most relays, though you can get 60A relays now. The relay coil requires a relatively small current (0.1A or less) to turn 'on'. Therefore, the wires to the coil do not have to be especially thick, and the relay can be turned on either by a light-duty switch or by electronics (transistors).
Some electrical items on a car use relatively high currents. For example, a 60/55W headlight bulb (60W for high beam, 55W for dipped beam) draws a current of up to (60W / 12V) = 5A. There are, of course, two headlights. On the Uno, there is a seperate fuse and wire for each side, but both of these fuses get their power from the same switch. So, the headlight switch must conduct a current of 10A.
Ohm's Law states that the voltage drop is proportional to resistance multiplied by current. The more current there is, the more voltage drop that a certain resistance will create. V = I * R. Now imagine that the headlight switch (and its connections, all the way through the wires to the headlight plug) are slightly less than perfect. Yes, really! A 0.2-ohm resistance would not be unfeasible. At 10A, that's a voltage drop of 2V.
That means, assuming that the battery and alternator are working at full strength (which, on the Uno, they're usually not), the 13.2V available becomes 11.2V at the headlight. See http://www.danielsternlighting.com/tech/relays/relays.html for the same discussion. You can see that light output (in lumens) drops off at a staggering rate. To quote that page, "The Europeans take a slightly more realistic with their voltage ratings; they consider output at 13.2v to be "100%". The loss curve is the same, though. When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal!".
In case you missed it, that means the average Uno headlights give about half the intended light output The standard switch (brass/copper contacts) and rather thin wiring is barely sufficient for the non-halogen 40/45W bulbs that were popular when the Uno was designed. Things get even worse if you think about fitting uprated (e.g. 90W) halogen bulbs.
A relay solves the voltage-drop problem because the resistance between the voltage supply and the headlight is reduced from 0.2 ohms to practically nothing. The existing headlight switch and wiring now only need to provide a small current to the relay coil. The relay turns 'on' and provides current through suitably-large wires straight from the battery/alternator.
So far, this has been about headlights - but the same situation applies to horns, heated rear windows, electric windows, and any other high-current devices fitted to a car. High power (P, in Watts) requires high current (A), or high voltage (V). P = VA. Fortunately, the Uno already comes with a relay for the heated rear window, and some models have a relay for the horns.
I talked about relays for electric windows in this post: https://www.fiatforum.com/uno-technical/81347-electric-windows.html?p=899346
How is a relay connected to the headlight wiring?
A typical relay, with mounting tag and socket base, is shown below.
On the Uno, the green/grey (one is high beam, one is low beam) wires need to be intercepted before they reach the headlight plug. Just cut the headlight plug off and solder or crimp connections to the wires. The concept is pretty simple - connect the relay coil (terminals 85 and 86) exactly where the headlight bulb used to be! The existing earth (black wire) will be sufficient for this. It doesn't matter which way around the relay coil is. But you will need two relays - one for high, one for low.
If you want to be really thorough, you would put another two relays onto the other side headlight wiring. But this is not really necessary. The only advantage is that if a relay fails or a wire falls off, you would lose only one light. I guess that's quite a big advantage!
So, you have a relay that clicks 'on' when the headlight switch goes on - great. Now you need a high-current supply to the relay. Use a 10-gauge wire to provide 12V to terminal 30 of the relay. It would be a good idea to have an in-line fuse, say 30A, as well.
There is an easy way to get suitable wire (red and black), fuse holder, fuse, and terminals - just buy an Amplifier Installation Kit from a car audio/car accessories shop
The fuse needs to be as close to the power source as possible so that any short in the wiring (e.g. chafing on metal) blows the fuse. One power source on most Uno models is a small black or white plastic box near the left suspension turret - it has ring terminals for the wires that connect to the battery. I like to use the starter terminal on models that have the starter at the front of the engine (e.g. 1116cc/1301cc/1372cc/Turbo). Use proper ring terminals and solder them if you are in doubt about the crimping.
So now the relay has a +12V (hopefully even +13.2V!) supply. When the relay turns on, terminal 87 gets 12V/13.2V. You need a wire from relay terminal 87 to the headlight bulb. This will be connected to the headlamp plug that you cut off previously. The terminals that had the green or grey wires are the positive supplies for dip/main beam. The wiring should be nice and thick - 10 or 12 gauge.
Don't forget the earth! The electrical earth or ground, that is. The black wire of the headlamp plug needs to be upgraded to a wire just as thick as for the positive supply. The other end of the wire needs a ring terminal bolted to the metalwork, such as at the earthing point near the battery tray.
Repeat for the high beam and either extend the wires across to the other side headlight, or install relays there and extend the power supply across. Use heatshrink tubing to cover soldered joints, tuck the wires into the corrugated tubing that runs across the front crossmember.
That's it!
Any side-effects?
Uno models made since 1986/1987, and possibly right up to the end of production, have a feature known as 'dim-dip'. This was only required in the UK at that time and is not required today. Dim-dip works by having a resistor (looks like a spring in an open tin box) attached to the sidelight circuit so that with the sidelights (first click of the headlight switch) on, the headlight dipped beams get a reduced voltage (created by the deliberate resistance). What a waste of time. Why would you want dim headlights with the rest of the energy turning into heat in a resistor?
The side effect of having relays, though, is that now the relays will turn on instead of the dimmed headlights - and the headlights will be full-brightness even with the switch in the sidelights position. (Note that the park lights, which are on when the ignition key is turned backwards, are not affected).
The potential confusion is that the main/dip switch will have no effect for the sidelights position (or, on the Mk2, the headlight main/dip lever will not move when rotated to 'sidelights').
The simple solution to the problem is to unplug the dim-dip resistor - and remove it! Then, the sidelights position of the switch will turn on just the sidelights (park lights). Problem solved
More reading
For a little more reading about similar situations with Italian car lighting, and a mention of the 'Duplo' bulbs (non-Halogen) that base-model Unos have, see
http://www.viva-lancia.com/fulvia/qanda/electrical/headlights.php
-Alex
The last time I fitted relays to headlights was years ago and I can't find the photos - except one (below) that shows the result - one of these headlights has the relay fitted, and the other uses the standard wiring.
I shall turn this thread into a guide - with pictures - when I next carry out this modification. In the meantime...
What is a relay?
A relay is an electrically-operated switch (the Italian term, Teleruttori, is a little more emotive, rather than the English that means a torch-passing race). There is a coil of wire inside the relay that forms an electromagnet. The switch contacts move (they are influenced by the magnetic field) when a current flows through the relay coil.
There are usually at least four terminals on a relay:
- two terminals (numbered 85 and 86) provide the power to the relay coil
- one terminal (30) has power connected to it. This is the moving contact.
- one terminal (87) is the other (stationary) contact. This becomes live when the relay turns 'on'.
- sometimes, there is another terminal, often numbered 87a. This may either become live at the same time as terminal 87, OR it may be live when the relay is off and become 'dead' when the relay turns on. This latter possibility is known as a 'changeover' or 'cutout' relay, useful for reversing the direction of a motor (e.g. electric windows https://www.fiatforum.com/uno-technical/81347-electric-windows.html?p=899346) or turning something off when something else goes on.)
The picture below shows a standard relay. Usually these are black but they can also be grey, green, red, blue, white, etc. The colour doesn't reliably indicate the type or function.
Sometimes, the relay is a taller or wider shape and has extra electronics inside to turn the relay on when there is a special signal on extra terminals, or after a certain length of time. Examples include fuel pump relays, central locking control relays, interior light delay relays, and others. You could say that the additional electronics make each of these 'relays' actually a 'relay plus control circuit', but people still think of them as relays (and get confused). Just think of them as 'control units' instead
The rest of this article talks about only the standard relay.Why use a relay?
The relay contacts can carry a large current - up to 30A for most relays, though you can get 60A relays now. The relay coil requires a relatively small current (0.1A or less) to turn 'on'. Therefore, the wires to the coil do not have to be especially thick, and the relay can be turned on either by a light-duty switch or by electronics (transistors).
Some electrical items on a car use relatively high currents. For example, a 60/55W headlight bulb (60W for high beam, 55W for dipped beam) draws a current of up to (60W / 12V) = 5A. There are, of course, two headlights. On the Uno, there is a seperate fuse and wire for each side, but both of these fuses get their power from the same switch. So, the headlight switch must conduct a current of 10A.
Ohm's Law states that the voltage drop is proportional to resistance multiplied by current. The more current there is, the more voltage drop that a certain resistance will create. V = I * R. Now imagine that the headlight switch (and its connections, all the way through the wires to the headlight plug) are slightly less than perfect. Yes, really!
A 0.2-ohm resistance would not be unfeasible. At 10A, that's a voltage drop of 2V.That means, assuming that the battery and alternator are working at full strength (which, on the Uno, they're usually not), the 13.2V available becomes 11.2V at the headlight. See http://www.danielsternlighting.com/tech/relays/relays.html for the same discussion. You can see that light output (in lumens) drops off at a staggering rate. To quote that page, "The Europeans take a slightly more realistic with their voltage ratings; they consider output at 13.2v to be "100%". The loss curve is the same, though. When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.22v), bulb output is a paltry 53 percent of normal!".
In case you missed it, that means the average Uno headlights give about half the intended light output
The standard switch (brass/copper contacts) and rather thin wiring is barely sufficient for the non-halogen 40/45W bulbs that were popular when the Uno was designed. Things get even worse if you think about fitting uprated (e.g. 90W) halogen bulbs.A relay solves the voltage-drop problem because the resistance between the voltage supply and the headlight is reduced from 0.2 ohms to practically nothing. The existing headlight switch and wiring now only need to provide a small current to the relay coil. The relay turns 'on' and provides current through suitably-large wires straight from the battery/alternator.
So far, this has been about headlights - but the same situation applies to horns, heated rear windows, electric windows, and any other high-current devices fitted to a car. High power (P, in Watts) requires high current (A), or high voltage (V). P = VA. Fortunately, the Uno already comes with a relay for the heated rear window, and some models have a relay for the horns.
I talked about relays for electric windows in this post: https://www.fiatforum.com/uno-technical/81347-electric-windows.html?p=899346
How is a relay connected to the headlight wiring?
A typical relay, with mounting tag and socket base, is shown below.
On the Uno, the green/grey (one is high beam, one is low beam) wires need to be intercepted before they reach the headlight plug. Just cut the headlight plug off and solder or crimp connections to the wires. The concept is pretty simple - connect the relay coil (terminals 85 and 86) exactly where the headlight bulb used to be! The existing earth (black wire) will be sufficient for this. It doesn't matter which way around the relay coil is. But you will need two relays - one for high, one for low.
If you want to be really thorough, you would put another two relays onto the other side headlight wiring. But this is not really necessary. The only advantage is that if a relay fails or a wire falls off, you would lose only one light. I guess that's quite a big advantage!
So, you have a relay that clicks 'on' when the headlight switch goes on - great. Now you need a high-current supply to the relay. Use a 10-gauge wire to provide 12V to terminal 30 of the relay. It would be a good idea to have an in-line fuse, say 30A, as well.
There is an easy way to get suitable wire (red and black), fuse holder, fuse, and terminals - just buy an Amplifier Installation Kit from a car audio/car accessories shop
The fuse needs to be as close to the power source as possible so that any short in the wiring (e.g. chafing on metal) blows the fuse. One power source on most Uno models is a small black or white plastic box near the left suspension turret - it has ring terminals for the wires that connect to the battery. I like to use the starter terminal on models that have the starter at the front of the engine (e.g. 1116cc/1301cc/1372cc/Turbo). Use proper ring terminals and solder them if you are in doubt about the crimping.
So now the relay has a +12V (hopefully even +13.2V!) supply. When the relay turns on, terminal 87 gets 12V/13.2V. You need a wire from relay terminal 87 to the headlight bulb. This will be connected to the headlamp plug that you cut off previously. The terminals that had the green or grey wires are the positive supplies for dip/main beam. The wiring should be nice and thick - 10 or 12 gauge.
Don't forget the earth! The electrical earth or ground, that is. The black wire of the headlamp plug needs to be upgraded to a wire just as thick as for the positive supply. The other end of the wire needs a ring terminal bolted to the metalwork, such as at the earthing point near the battery tray.
Repeat for the high beam and either extend the wires across to the other side headlight, or install relays there and extend the power supply across. Use heatshrink tubing to cover soldered joints, tuck the wires into the corrugated tubing that runs across the front crossmember.
That's it!
Any side-effects?
Uno models made since 1986/1987, and possibly right up to the end of production, have a feature known as 'dim-dip'. This was only required in the UK at that time and is not required today. Dim-dip works by having a resistor (looks like a spring in an open tin box) attached to the sidelight circuit so that with the sidelights (first click of the headlight switch) on, the headlight dipped beams get a reduced voltage (created by the deliberate resistance). What a waste of time. Why would you want dim headlights with the rest of the energy turning into heat in a resistor?
The side effect of having relays, though, is that now the relays will turn on instead of the dimmed headlights - and the headlights will be full-brightness even with the switch in the sidelights position. (Note that the park lights, which are on when the ignition key is turned backwards, are not affected).
The potential confusion is that the main/dip switch will have no effect for the sidelights position (or, on the Mk2, the headlight main/dip lever will not move when rotated to 'sidelights').
The simple solution to the problem is to unplug the dim-dip resistor - and remove it! Then, the sidelights position of the switch will turn on just the sidelights (park lights). Problem solved
More reading
For a little more reading about similar situations with Italian car lighting, and a mention of the 'Duplo' bulbs (non-Halogen) that base-model Unos have, see
http://www.viva-lancia.com/fulvia/qanda/electrical/headlights.php
-Alex
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