MGB Register Forum

Hi all, engine turns over but will not fire, tries to but doesn't run. This is the symptom of a faulty ballast resistor.
The Story From The Beginning::: The starter motor packed up and was due to faulty connections at the rear, new part fitted but didn't have the small terminal for the w/lg wire so I made a term and fitted it to the large solenoid term'l stud. I refitted the starter and the distributor, its electronic and a DLB102 coil is also fitted.
With the ignition turned on(position two) there is 0.5 v at the + on the coil,w/lg wire, and 10.7v at the white wire at the ignition relay.
With the wires disconnected at the coil, the ignition relay and at the fuse to the radiator fan the ballast resistor measures 1.9 ohms.
The coil tests ok and there is a spark at the plugs when turning over the engine thus proving the w/lg from the starter motor to the coil.
Should I adjust the wiring and fit an external ceramic resistor or maybe fit a 12v coil with the electronic ignition thus cutting out the loom ballast resistor and running a white wire direct to the + on the coil? Will this work with the 2M100 type starter motor or will I need to fit another relay that comes into play when the key comes back to position two from three(the starting position) thus allowing the voltage to the coil and the engine to run.
I'm stumped as to what or where the fault is.
Any help appreciated,
Thanks Sean.

Hi Sean
For some reason I think you are losing the power to the coil when the ignition key is turned to position 3. So check this part of the wiring using the wiring diagram.
If you have a spark at the plugs when the key is in position 2 the engine should then continue to run after cranking it over.
An alternative is that the battery doesn't have sufficient power to allow cranking and power the ignition, hence no spark. Make sure the battery is fully charged.
Also can you hear the fuel pump ticking?

Knowing the age/model of the car would help provide you with more suggestions. (Edit: Sorry I see it is a 79 car in the title! Is it an LE just in case that makes a difference?)

Hi Peter,
Thanks for your reply. I am following the wiring diagram in the Haynes manual for UK '77 and later cars. The battery is charged ok. It is not an LE.
Yeah I am losing power at pos 2. Pos 3 is the cranking pos and the full power comes to the coil on the w/lg and gives the spark, I am getting a spark ok.
With the key at pos 2, the run pos, everything works, pump, horn,hazards, lights, I am getting 10.7v at the wh/wh at the ignition relay and at the wh going to the radiator fan but 0.5 v at the w/lg at the coil.
This led me to believe the ballast resistor was faulty!! but if I test the resistance from the wh/wh, disconnected from the relay, and the wh to fan dis, to the w/lg at the coil, disconnected, I was getting a reading of 1.9ohms. Info from the site mgb-stuff.
This has stumped me. Is it a High Resistance connection in the loom? Would it be worth it to open the loom to investigate or connect an external ceramic resistance and wire it in, with the loom ballast and wires disconnected of course. Do you have an idea where the conns are in a loom??
Thanks again.

Hi, electronic ignition does fail, mine did recently after only 2 years, and can be damaged if connected up round the wrong way. I was able to replace the electronic module inside the distributor with a set of contact breaker points & condensor, and it's been fine.