My 68 +2 has three relays on the passenger side wing, by the fuses. Two are inboard of the bracket (engine side) and one is outboard. The outboard one is clicking a lot, I can hear it in the car, sounds like an SU fuel pump on empty... so I thought I should replace it. However I've looked in the Workshop manual but can't seem to make the wiring codes marry up with my car.

There are 4 terminals, in a cross shape. If I look at the bottom of it, holding it with the mounting lugs at the top (12 o'clock), the wires are as follows - North, white with green trace. East, white with yellow trace. South, heavy duty cable, white only. West (spade is marked W1) red wire linking to East .

I'm thinking this could be the main beam relay, but the colours are all wrong according to the circuit diagram. No markings on the relay case, it's black plastic.

I've bought a Lucas 6RA 4-spade relay to replace it with, but unless I can work out both what it does and which wires are which I don't really want to touch it ! Anybody have any ideas ?

Hi Shiny kit, you don't say what your failure systems are showing as: eg, headlights intermittantly switching on or off as opposed to a clicking noise from the relay which could easily be a earth fault, switch fault, device fault etc etc.

Secondly, if you want to see if the relay itself is the problem, test the device off the car. Vast majority of relays have two contacts for the coil, two separate contacts for the load. Sometimes the coil and load share a contact. You should be able to work out if the relay is normally closed (vast majority and only switches the contact for the load when the coil is energised), or normally open (load contacts are closed and open when the coil is energised). Occasionally you see switching contacts (these should have 5 contacts).

As you say, relay is plastic so not original and wiring may be the same.

Using a 12V test setup (12V in series with a say headlight bulb), check the current draw across the contact sets. Assume first the smaller wires are for the coil. The Bulb should glow very faintly when connected across these. Then check across the terminals with the big wires, the bulb should not glow at all (Normally closed). Lastly energise the coil and check with the 12v test setup across the terminals for the large wires. This should now glow brightly.

Now you have figured out the coil functionality, replace with your new coil.

Regards

Hi. It may help to get yourself a cheap digital volt meter such as sold by the likes of maplin - only £7 last time I looked. With this you can check the resistance between terminals, and also check the on resistance of the load contacts.

I have a '72 +2 and have no relays or fuse box to speak of other than those on the dash - I need to spec up what I need.

All the best.

Sean.

Sean, by 1972, Lotus had decided to simplify the Plus 2 wiring and do away with relays. In theory the wiring is protected by thermal switches instead. Without saying anymore, this method of protecting wiring didn't catch on...

Most relays have the terminals marked: 85 and 86 are for the coil; 30 is 12V
supply from the battery, and 87 is the load terminal feeding whatever you are operating with the relay. PM me if you need further information. I check my e-mail most evenings when I get home from work.

Thanks guys. Unfortunately only one of the existing terminals is marked but at least I know now what I am looking for. To be honest it may not be the relay which is at fault, I have seen no "symptoms" other than the clicking of the relay, but then I havent used the lights as I don't take the +2 out at night !

I used moder type relays. See attached photo. When you are checking relay function off car determine internal circuit and attach to modern relay using schematic molded into case.

Bob

One aspect to keep in mind when replacing relays, especially with non original items is that due to the coil inductance, you will get a back emf which will cause a voltage spike. This may affect any electronics you have added into the car (eg electronic voltage stabiliser, electronic ignition) if the back emf exceeds the rating of the new devices you have added. With modern compact relays, you might also see the load contacts welded closed. It's good practice to limit these effects (use a MOV: metal oxide varistor or diode etc). Some relays have these built in.

Regards

I looked at buying some "modern" cube style relays from Vehicle Wiring Products, but thought they look a bit too modern (not that I am usually an originality freak but the old-fashioned Lucas metal cans look much better in a classic engine bay). Providing they work of course !

I have a 69 S4 Elan & the relays in it have a black plastic case not the metal one. I don't know if the +2 is the same but the forward relay in the Elan controls a flasher unit. If the headlamps are turned off & the headlamps are raised then the lamps flash on & off. Maybe this is the same in the +2 & what you are hearing is the flasher unit?

Did some more investigating today and it's the horn relay - at least I know what it does now !

Shiny Kit:

Horn relay is helpful info. The wiring colours you have were quite confusing, as they are not following the Lucas standard. At any rate, a few general comments that might help without totally confusing.

The horn wiring is switched to ground by the column button. This is a bit different than the 'usual' wiring of relays where they are switched on the hot side.

The horn circuit, without the "burglar feature" described below, is as simple as it gets, requiring a four terminal "make and break" relay. The relay of this type is a simple normally open switch. The replacement relay you require (modern or vintage) would have four terminals only if you are setting up a simple horn circuit.

Your post mentions four terminals on the original relay, but the replacement one sounded like a five terminal change-over relay when I Googled it. Could just be a part number confusion?

One feature to be careful of in the stock Plus 2 horn circuit is to check whether your car is/was equipped with the shut-off switch in the glove box, and what is it current state. Moving this switch causes the horn to sound if you try to start the car. Don't know if you have/had this feature; it was originally on my Plus 2 but is now removed. Once spend a half day at the side of the road figuring this out on a friend's Plus 2, and it involved mysterious (to us at the time) relay clicking. Solution involved a tow truck and the dealer, so not specific much help here. Check and understand this circuit carefully in your car if present or in the original, as I understand failure of the glove box switch can be quite common and this is a favorite for modification by a previous owner. Ask if you need more; not looking at my diagram right now, but the white/yellow is a standard colour for the coil so I suspect this circuit is involved in your set-up. I can't remember details right now, but had it figured out at one time. Note my book is for Federal Plus 2 and may be different, so any further detail would probably be confusing.

W1 and W2 (apparently standing for "winding") are Lucas terminology for the relay coil, the part that gets the relay input. This is equivalent to modern relay terminals 85 and 86.

C1 and C2 (apparently standing for "contact") are Lucas terminology for the load side of the relay. This is equivalent to modern relay terminals 30 and 87.

The red jumper wire you report is likely going from W1 to either C1 or C2. It has to be going to one of the C terminals, otherwise it would be simply shorting out the relay function. The purpose of this wire is likely to provide a common ground or power to the circuit, but this is where your wire colours get a bit confusing to me, although I haven't looked closely.

The jumper wire configuration can be used to create a kind of 'latching relay' action, where intermittent powering of the circuit acts to hold the relay on after it is powered up. Quite confusing to describe, but this type of circuit is used on the later Plus 2 side lights with the flat switches. Speculating here, but wondering if this relay acts to ground the coil and continuously sound the horn if the coil positive is momentarily powered with the 'burglar feature' set in the no-start position. As I say, speculating and any more would just confuse.

HTH

That's really useful, thanks. I don't have the glovebox switch (or if I do, I haven't found it !) but there is a battery cut-off switch (racing style) mounted by the drivers right knee (right hand drive UK car) under the dash.