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MG Midget and Sprite Technical - Midget 1500 compatible coil

Hi there.I bought a 1978 midget 1500 two years ago.I drove it home 180 miles and it ran like a dream.It has been off the road since while I worked on it.I drove it yesterday 30 miles and it started to cough and splutter and then stalled.It would spin over really fast but not start.Then it would sound like the battery was flat and hardly turn over.When I looked under the bonnet and found that the coil was red hot to the touch.I left it all to cool down,and it started no problem and got me home 30 miles the other way.I've looked through archives about ballast and none ballast coils.My coil is the Lucas sport DLB105 linked to electronic ignition not sure of the make but it 27/AE-V5 marking on the connection inside the distributor.I've looked at info saying that this coil is not compatible with the 1500. Could someone give me their thoughts if this could have been the problem.cheers
P LATHAN

You should be able to go to any auto parts store and have them look up what the correct coil and purchase it there ... probably in stock.... there less then $50

Prop
Prop and the Blackhole Midget

Hi, and welcome.
It could be the problem but coils can run quite hot. Having done 180 miles in the past would suggest it's not the problem unless it's "gone off" whilst standing.
(According to t‘interweb) the DLB105 is a 12v non-ballast coil and shouldn't be used in a 1500 unless other wiring changes have been made to accommodate the electronic ignition module.
To give a more definitive answer we'll need a bit more info to understand how it's all connected up. How is the electronics unit wired in and what cables are attached to the coil terminals?
Pictures always help...

Best of....
MGmike
M McAndrew

Hi there.thanks for getting back.hopefully the photo uploads.one terminal has a piggy back with two green and white wires and on the same terminal there is a red wire which goes to the distributor.the other terminal has two white and black wires and also a black wire which goes with the red wire wire back to the distributor.hope that helps.
P LATHAN

No photo.will try again.
P LATHAN

I hate to pile on, and add confusion

But alot of time when the coil is extremely hot its because of a double grounding

Like a chaffed igintion wire making direct contact to a sheet metal panal, a self taper screw inadvertly screwed.thur the wire, or the wire got pinched

But id focas on getting the correct coil 1st and see if that fixes the problem, then persue other avenues if it dosnt.

For no more then a coil costits worth it if your not well.versed in auto ignition, or your just going to be chasing your tail for the next 6 months

Prop
Prop and the Blackhole Midget

Check the voltage at the coil i have a 1500 and it has a 12 volt coil with electronic ignition when i fitted it i ran a new wire and removed the balasted wire .
mark 1500 on the road Preston Lancs

Cheers everyone. Which one would be the ballasted wire then? Do you check the voltage on the terminal with the green and white wires? Sorry can't see any + or- on the coil?
P LATHAN

Hi,


The ballast wire in integral with the harness, its a special white/pink wire in series from the ignition switch to one on the green/whites at the coil +.


The other green/white comes off the bypass wire at the starter solenoid and bypasses the ballast to give cranking voltage when starting.


Most aftermarket electronic system need running voltage, which yrs isn't getting atm. It probably needs a new wire running to it off the unballasted ignition circuit.
SR Smith 1

Whoa hold on boys…

Let’s work through this a bit logically when we have all the pertinent information and not just chuck stuff at it. That’s almost always going to add problems.

Prop, chucking a coil at it (even if they are only $20 over here) is akin to chucking a head gasket in for HGF without checking the heads flat and you know where that takes you ;-)

Let’s reflect on what we know so far..
The two green and white wires on the coli are as expected, one will go to the ignition switch via the ballast wire in the loom and the other will go to the starter solenoid to provide the bypass for starting. The red wire is the supply for the ignition module which may or may not be in the correct place dependent on the requirement of the module.

The two black and white wires on the other side of the coil are also as expected, one goes to the tacho and the other should run to the distributor to supply the original points system (probably disconnected at the dizzy end because of the electronics unit). The black wire runs to the ignition module and may or may not be in the correct place (although I belive it is).

The coil is a 12v non-ballast unit and the car stops when it gets hot!

Putting a new coil on might allow the car to run but my bet is that it will still stop when it gets hot and our question should be “is there some other cause of the failure or is the coil in fact failing”?
My bet is it’s something else but to confirm it I’ll need more information on the wiring requirements of the ignition module. Without these we are guessing as to how it should work…. But as we are here’s my theory….

The heat in the coil is causing the resistance to drop to the point where the voltage at the green/white (+ve) drops below the threshold required by the ignition module and, as a result, it stops working (until the coil cools down).

Therefore I believe the ignition module is wired incorrectly and possibly the wrong one for a ballast system. The red wire should go to a switched 12v supply (my choice would be to the white wire on the fuse box). The black wire is okay where it is but I would tidy this up by connecting to the white and black at the dizzy end (assuming they are two separate wires to the ignition module and not sleeved together). The coil should be changed for a ballast version but only if the ignition module can support it (which is another reason why we need to know the type and requirements of the module). A ballast coil will have a much higher current flow when in the ”bypass” starting phase and the module needs to be capable of carrying this higher current. Therefore fitting a new ballast coil might blow the ignition module and is probably the reason for the non-ballast one being fitted in the first instance. Putting a new non-ballast coil might fix it for a while (or run happily in the winter!) but there again it might not…

My recommendation is to find out what ignition module is fitted or replace it and the coil with units designed for a 1500’s ballasted ignition.

Best of...
MGmike
M McAndrew

Hi again,

As far as I am aware the after market electronic systems don't come in ballast or non-ballast versions?


It's just a case of working out which one you have fitted as Mike says.


From you're description it sounds like all the gubbins are internal to the dizzy? Maybe be Magrtonic/Petronix?


Lumention has a 3 pin plug linked to an external module with a red live, black earth and a violet trigger wire.



A pic would help.



SR Smith 1

Hi all. Sorry for the delay. I have been taking some readings.i am getting 8 volts at the positive side of the coil,which suggests it is ballasted,which postings say would need a 1.5 ohm coil.unfortunately I am getting a reading of 3 ohms which suggests it is not compatible with the system.inside the distributor is a small rectangular black box which has the markings 27/AE-V5 which replaces the points.Would the easiest thing be to do is to replace the coil for a 1.5 ohm one?I have tried putting photos on,but after message saying that have been uploaded,nothing is.Will try again.thanks all for your patience
P LATHAN

You have a 12 volt coil which shouldn't run hot if it's only being driven by 6-8 volts and switched normally by the ignition module. If this is failing and switching on it will "saturate " the coil and cause it to overheat (maybe)
The module uses a high voltage specially designed switching transistor which, theoretically, can handle any coil. If it is failing because of insufficient voltage drive,(as suggested by MG Mike)then you can fit a relay driven by a separate feed from the ignition switch to supply 12 volts to the ignition module and the unballasted coil which will also improve spark energy by raising the voltage at the coil.

On of the wires from the coil is the tacho drive. This is the extent of my knowledge. Good luck, Cheers
Rod
R W Bowers

Before I dive in and make a silly assumption (which is always possible for me :-)) can you confirm the 8v is measured with the engine running or at rest?
If at rest could you remove the red wire to the ingnition module and remeasure?

Best of...
MGmike
M McAndrew

This thread was discussed between 17/08/2015 and 28/08/2015

MG Midget and Sprite Technical index

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