Ignition ballast bypass removal

One of the major sources of poor starting on dolomites, especially the slant 4 engined variety like sprints and 1850's is the ballasted ignition system.

There is nothing wrong in concept with a ballasted ignition system. It works like this....when running normally the ignition low tension side of the coil is fed by a 6 volt supply. At starting this is increased to full battery voltage, so that the coil gives out a bigger spark and this compensates in no small measure for the otherwise reduced output caused by the voltage drop from the battery as it turns the engine over with that current sapping voltage reducing electric starter motor.

So how do we get a 6V supply at the coil when the battery gives us a nominal 12V? (Its actually 13.2 or somesuch for a well charged lead acid accumulator, but you all knew that). Well electrickery being what it is we need to bring Ohm's law to the situation. More later... Volts = Current Times Resistance or V = I x R

Ergo if you add a resitor in series with the coil and it matches in Resistance, you get half the volts across the coil and half across the resistor... the ballast resistor. Simples....a 6V coil is used.

So when its time to start, just arrange the wiring so that the ballast resitor is bypassed.

The problem with ohc dolomites is the way in which this is done...fine when the cars were new and it was warm and dry. Not fine after 5 minutes and its raining.

So to bypass the ballast resistor you need another wire that comes direct from your ignition switch and operates when you turn it to the start position. You wouldnt have thought it was that hard to arrange would you? You havent met my friends Sir John Black and Joe Lucas then have you? (Actually it was probably one of Spen King's cronies by then but we digress) Now Mr Lucas concocted a very clever switch that did a nice extra position for switching on your radio without the ignition on, but missed the ballast bypass feed point entirely. It just has a big fat feed for the starter solenoid....

So no worries said the cronies...we can take the feed from the starter solenoid. A fine idea when the solenoid is nicely sitting on a dry bulkhead nice and high up away from the mess, like it is in spits and mini's and lots of other fine starters, but NOT on a slant engined Dolomite. Here the solenoid is on the starter and sits in that nether region between the hot exhaust and the damp and dirty road. Not a good place for a good long lived and relaible electrical contact then, and so it proves.

As time and tide take their toll on lucas's finest wiring looms, the contacts at the solenoid stop functioning and the ballast bypass feed degenerates through corrosion and neglect or just falls off altogether. Result is a fine running dolomite that somehow seems a bitch to start all of a sudden, and much head scratching and points changing on the part of the uninformed owners...

Now you read this and you dont have to be one anymore....

So if your dollie wont go, you can dive under the car and wiggle the ballast bypass wire at the solenoid. Its quite clever that you can tell the 2 wires....the solenoid feed has a nice big connector, and the bypass feed has a small and weedy one, with a tendency to drop off. So having burned your hand on the hot exhaust or got soggy in a puddle that you just parked in, you must be thinking there is a better way....

There is....its called a 12V coil.

You dont NEED a ballasted coil at all. All you need is a 12V coil that just works at battery volts all the time. Said coil then just needs to produce a decent spark voltage, enough to jump a 30 thou gap in the presence of petrol vapour and set it off....bang, down goes your piston and off goes your engine, and then you.

So where can said 12V coil be found? Well if you are a tightwad like me then Nippon Denso make a particularly fine one that lives under the bonnet of a dead Nissan micra or Almera at your local scrappie....and they run for ever.

Or you can just get one of Joe Lucas's finest that currently retail for about 20 quid and are used on Mini's and MGB's etc. The Gold sports series are quite good and the number is DLB105. They even come with the right connections. The ballasted equivalent is a DLB 110. Don't buy one of those by mistake.

The coil lives on most ohc dolomites on the bulkhead by the bonnet latch. Its held on by 2 bolts....well actually the brackety for the coil is held by 2 bolts, but most coils come with the bracket as a part of the deal. Just put the new where the old was....

For the chosen few who have a stromberg equipped early dolomite, the coil is on the inlet manifold and the ballast resitor is that white oblong thing with wires all over the place beside it.

Now the electrical bit. The coil minus has a lead that goes to the distributor.....keep that the same. It also has a grey and white wire for the tacho. Keep that the same too. The bit that needs changing is the supply voltage that goes to the coil plus. On most later slant engined dolomites the ballast resitor is actually a lenth of resistance wire in the loom from the ignition switch to coil plus. This goes to the same terminal as the ballast bypass feed. The 2 wires may be crimped to the same terminal or they may be seperate. Take off these wires to the coil plus and replace it with a feed taken from the fuse box, a short distance away on the drivers side of the bulkhead. You need a lead long enough and a couple of the right lucar connectors and a crimping tool to make your own. Take the feed from the white wire connection at the fuse box. This is the ignition fed fuse that is powered at full battery voltage when you switch on the ignition, so its just what you want. The green side is for your wipers indicators and everything else that only works when the ignition is on. You will see there is even a spare spade terminal there for you to use. Run a wire straight from this to the coil plus and thats it. Please dont use the green side...you dont want your ignition to go off when a fuse blows do you?

You can just leave the original coil plus connections there and tape it up safely out of harms way, but disconnected.

Try and start your car, and away it will go....1st turn of the key I suspect.

If this doesnt work then something is wrong.... so its out with your voltmeter and spare spark plug and lead and diagnose away. You will soon find it. What do you mean, you dont have a voltmeter? Go and buy one....a few quid at Tandy or on ebay.


Now a short extra note for those with electronic ignitions....

I have seen quite a few cases where the supply for the electronic ignition module is taken from the coil plus. With a ballasted system this can lead to poor triggering and misfires. The electronic ignition module really needs a bit more than the 6V available when running (not starting) at the coil plus. Its better to supply it from the same place as the non ballasted coil....the white wire terminal at the fuse box.

Some electronic ignitions will function with the ballasted system, because they can cope with the 7V or so that is available when the car is running and the alternator is charging. But what happens at night in the rain with lights and wipers on. You voltage could well then be dropping to half of 11V and your ignition will misfire.


Happy igniting.

I found this article on the Dolly Wiki a online reference for the Triumph Dolomite and its derivatives https://www.dollywiki.co.uk/wiki/Main_Page