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MG Midget and Sprite Technical - Resistance Wire

A guy I kinda know has a 1976 midget and is trying to sort out the ignition. I do not believe he has ever seen this car start. He has the American-style Opus electronic ignition. Yes, he knows that it is a liability, but he wants to try to get it to work. Is there any opus-specific testing that can be done?

According to the wiring diagrams, there is a discrete resistor between white and the distributor AND a resistance wire between white and the W/LG that connects to the + side of the coil. Can anyone tell me what colour the resistance wire is? There is a red/black wire there which is a strong candidate, but I like to be doubly sure whenever possible, especially if there is a chance that the Opus is not yet fried, since I do not want to be the guy responsible for letting the smoke out.

While you are at it, take a look at the 3-wire connector to the Opus module. One end is pointed. From the pointed end, what is the colour sequence on the wires from the wiring harness? There is a White, a White/Black, and a White/blUe, but I have seen a couple different indications of the order and would like to be sure based on someone with a working Opus (if such a person exists).
David "trying to be helpful" Lieb
David Lieb

David:

My 1979 Midget for some reason is co-wired for both the EID-Opus and CEI ignition units. They are interchangable. Below is a pic of the plug in the car: pointed end white/blue, then white in center, white/black on squared end of plug. FWIW, the Opus unit (from a '78 Spitfire) has a red/black wire in center of it's portion of the plug, the other 2 wires match the layout stated above. Cant help with the resistance wires yet, too cold and dark out there!

R


Richard 1979 1500

David;

Email me off line but in the meantime there is some checks you can do.

You'll need a 0-20V voltmeter, an ohmmeter and for some reason a hydrometer. Guess that's for checking the battery specific gravity.

It is suggested that you do a high tension circuit check. Disconnect the high tension lead from the distributor and hold it 3/16" from a good ground. Turn the ignition on.

Disconnect the white/blue lead at the drive resistor and check for a spark at the HT lead when the white/blue laed is disconnected. Weak/no spark, replace the ignition coil high tension lead. If a good spark present, check all HT leads for deterioration and replace as required.

Remove distributor cap and check rotor. Hold HT lead 3/16" from rotor, turn ignition on and disconnect white/blue lead from the drive resistor. If spark occurs, rotor is defective and needs to be replaced.

If HT checks do not solve problem, additional testing is required. If problems are found to be in the amplifier, pick up module, timing rotor, the distributor must be replaced.

To check pick-up module air gap. (.014-.016 but BE CAREFUL NOT TO DAMAGE THE PICK_UP MODULE CORE WHEN INSERTING FEELER GAUGE (that's how it's printed in capitals so I guess it's important!) Reposition the pick-up module if necessary and check for spark. If no spark, check supply voltage, ballast resistor, drive resistor, distributor ground, ignition coil and distributor.

Disconnect the supply wire at the balalst resistor and turn ignition on. Check supply voltage by attaching red lead of the voltmeter to the supply wire and black lead to ground. Less than 9v, fault in low tension circuit between battery and ballast resistor. More than 9v, reconnect the supply wire and check voltage at ignition coil positive terminal to determine condition of the ballast resistor.

Connect red lead to positive terminal of coil, black lead to ground. Turn ignition on. If voltmeter reads 4-8v, the resistor is ok. More than 8v or less than 4v, the ballast resistor is defective and needs to be replaced.

Drive resistor:
disconnect the supply and out put wires at the resistor. Using ohmmeter check resistance. Should be 9-11 ohms. If outside the specs given, replace the drive resistor.

Distributor ground. Use the ohmmeter to check ground connection between distributor body and engine. If incmplete ground indicated, remove distributor and clean contact areas between distributor and engine.

If the preceeding checks have been completed and are satisfactory the coil and distributor must be substituted to correct fault. FIRST substitute ignition coil. If taht works do not replace distributor, (no kidding!). If that does not correct fault, replace distributor, replace the new coil with the original and check engine performance.

Anyway, that's what the British Leyland electronic ignition manual I have here says about the electronic ignition system.
Clive Reddin

Thanks guys! I am passing the info on to Tracy... Should keep him busy and out of trouble for the foreseeable future!
David "Not sure whether I actually am being helpful or not" Lieb
David Lieb

Perhaps there is a condenser to go wrong?
David "I told him to use the pertronix" Lieb
David Lieb

Well, the testing revealed that the Opus module is indeed dead. The Pertronix is now in place and running nicely. It is always good to know that the piece of Lucas being discarded really is dead.
David "long live Pertronix" Lieb
David Lieb

Good to hear. Hope he has the same good luck I've had with my PerTronix. Hasn't missed a beat!

-:G:-
Gryf Ketcherside

Is the Lumenition system the same as the OPUS one?
Clive Reddin

This thread was discussed on 31/12/2008

MG Midget and Sprite Technical index

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