Electronic ignition coil wiring

[John R]

Hi All
I'm nearing the end stage of the rebuild of my 1973 TCS but a little uncertain of the coil connection and really appreciate some help.

From the coverted electronic ignition distributor I have a black and red wire which I believe should go to the distributor. My guess would be read to positive and black to negaive?

From the wiring loom I have the following wires:

2 x Yellow/black (or could have originally been White/black)
2 x White (or may have originally been White/yellow)

Really not sure where these go and appreciate any pointers....

Thanks

[SilverBeast]

I'm a little confused by your wording.
(i) Do you have the instructions for the electronic ignition installation, or are you refitting one that was fitted by someone else? Do you know the manufacturer model etc?
(ii) Have you looked at the wiring diagram http://www.lotus-europa.com/manuals/misc/electrical/tc-uk-diag.gif? I'm assuming you have a UK Special. I believe the wiring is pretty much the same for TC and TCS as it doesn't have the extras a Federal TC has (I have a late 73 build TCS)
(iii) Have you replaced the ignition coil as well? I believe (mainly from reading this forum) some kits can be particular about the coil and can damage the coil if the ignition is left on without starting the engine.

Apologies if I'm repeating what you know already but from the above wiring diagram.

As you can see as standard
a)  There is only a single white/black wire between coil and points.
b) The ground will be via distributer body.
c) The solid black line between the coil and distributor is the HT lead.
d) The White wire to coil is the switched live from the ignition switch.
e) The White/Yellow from starter solenoid to coil probably isn't needed by you as I believe it just applies a full voltage to the coil during cranking for a stronger spark, which probably isn't needed with electronic ignition conversion (someone will correct me if/when I'm wrong)

From here on I'm guessing without details of the electronic ignition kit.
Your kit may need a permanent switched live (only on when the ignition is on to run the car to power the electronics) which logic would dictate would be red.  I would assume this would get the ground connection through the distributor body. This would only leave the black to be connected to the Whit/Black to trigger the coil and generate the spark.

Obviously you should check my logic and wait a while for further comments by other members (most of which have more experience with Europas than me), and proceed at your own risk.

Hope this helps.
Richard

[jbcollier]

The stock TCS uses a coil without an internal ballast.  Power flows from the ignition switch via the white wire to an external ballast resistor and from there to the coil +.  When cranking the engine, a terminal on the starter is energized and feeds power directly to the coil + via the white/yellow wire bypassing the ballast resistor.

We can't comment on how the red and black wires from then distributor should be hooked up until we know what system you have.  Any idea?  If not, can you post pictures?

As for the wires in your harness, I think you have one white, one white/yellow, one white/black (goes to tach) and one white/black (goes to distributor when points used).

[4129R]

Some electronic ignition distributors have a separate earth wire, and do not earth through the body of the distributor.

Someone correct me if I am wrong  please, but presumably the black wire from the distributor needs to go to earth. 

[jbcollier]

No, not necessarily.  In the Pertronix set up, red goes to coil + and black goes to coil -.  Red powers the system and the black charges and fires the coil.

However, don’t hook it up this way unless you know for sure it’s a Pertronix system.  Modules are easily fried.

[John R]

Thanks to all for the comments. 
I eventually found out that the conversion was made with a "Ultra Spark Ignition kit" and once on their site I found the wiring diagram.  (attached) It looks like the only wire I need to connect is the white wire from the ignition switch?
Cheers

[SilverBeast]

Your car is negative earth, so the bottom diagram.
(i)  Red to Coil+, which is where the White wire attachs from the ignition. You will probably need to run another wire, unless the red wire is long enough.
(ii) Black to Coil- which should be where the White/Black wire that was originally connected to the points is connected so you will be able to use that.

White/Yellow probably doesn't need connecting, but connecting to coil+ is probably Ok (It will be at +12V while the starter is cranking the engine). If you don't connect this then make sure you insulate the wire and/or disconnect it from the starter motor solenoid.

Good Luck.

Richard

[jbcollier]

Ok, electronic ignition hook-up sorted, next the coil.

First you need to sort out what type of coil you have.  Measure the primary resistance by hooking one test lead of an ohm meter to + terminal and the other to the - terminal.  You need a minimum of 3 ohms.  If it is less, you need to either fit a separate ballast resistor, or, fit a "12v" coil (has an internal ballast resistor).  Report back on what coil you have and we can tell what you need to hook up where.

[John R]

Many thanks for the advice.

I measured the resistance on the NEW coil as 2 ohms so it seems I either need another new coil or to fit a ballast resistor. Appreciate any recommendations on either.

Also I was wondering if you can help to place a "free" purple wire with no obvious home? When the ignition is on it is live. (see photo, the wire has a blue connector I've added to isolate it.

Cheers

[John R]

I found this coil on E bay - wuld it be suitable?

https://www.ebay.co.uk/itm/170625630589?hash=item27ba14817d:g:w~gAAOSwN8JefKkL

[jbcollier]

That's even lower resistance.

You have two ways forward:

- find a "12V" coil with a primary resistance of a minimum of 3 ohms.  Hook up the white harness wire and the red distributor wire to coil + and the white/black harness wire and the black distributor wire to coil -

- use your existing coil with a ballast resistor.  White harness wire to the ballast resistor.  Wire from other ballast resistor terminal, red distributor wire and white/yellow from starter to coil + and white/black harness wire and black distributor wire to coil -  This has the benefit of giving a spark boost during cranking, useful at -20°

What would I do?  Get a "12v" coil and go with the simpler wiring.  Good, easy to find, 12v coils are the "Bosch Blue" coil and the Lucas Sport coil.

[4129R]

Also I was wondering if you can help to place a "free" purple wire with no obvious home? When the ignition is on it is live. (see photo, the wire has a blue connector I've added to isolate it.

Cheers

That wire is not purple, it is brown, and used on some alternator connections.

[John R]

Many thanks. I believe the way forward is all clear now - I'll go for a new coil and permanently isolate the brown wire.

Cheers
John

[John R]

FYI I have been recommended

https://simonbbc.com/Viper-Dry-Ignition-Coil-Sports-Lucas-DLB105-SILVER

OK?

[jbcollier]

Yup, good choice.