Lucas AB14 ignition module/amplifier

My car is fitted with the Lucas AB14 ignition module. As the car has never run I have no idea whether this works- but I am also aware that it is a common failure point. I had therefore acquired a spare a long while ago- likewise I don't know if that works but then two possibilities are better than one! I also know that although the price of new units is ridiculous, several reports have stated that there is little inside them- and what is present can be changed much more cheaply than the cost of a new unit. I suspect that I will be returning to this particular blog later to update on problems with getting the car to work- but for now its a simple description of what the unit is like and how to take it apart.

My spare AB14 has obviously been stored badly and as its a wet day that's preventing me from getting under the car I thought Id take a look inside and at least clean up the contacts ready for use if I need it.

My spare unit was pretty battered looking...

 I removed the back by unscrewing the 4 x 3/16 or 5mm bolts

 and the back can be lifted off.

Inside there are 3 components: a zener diode (Top right), a Lucas DAB125 ignition module (or equivalent; top left)  and a capacitor (bottom left). The first thing that struck me is that the DAB125 is described as a 4 terminal ignition module yet it has 6 wires connected to it! In cases where the unit has failed I would guess replacing it with a Lucas item would be best but it may be tricky to find an original Lucas module. There are however plenty of cheaper alternatives (intermotor 15210) but not all users have found them satisfactory.
 The unit was pretty dirty inside- whole generations of spiders have clearly lived and died in there. There is a fair bit of corrosion- both white oxidation of the aluminium case and rusting- especially around the capacitor. The capacitor is also easily removed with the 5mm socket- it seems to be marked as Lucas 07/88 1MF capacitor.  This is I think a 1 microfarad capacitor despite the designation "M". The only catalogue numbers  I can find are Lucas DCB101 or Intermotor equivalent with number 33710. However these are only 0.22 microfarads and I suspect arent really correct. I cleaned up the mounting lug and the box where it fits. I then treated them all to a smear of dielectric grease. Finally I measured capacitance and obtained a reading of 1 microfarad.

The ignition module is a Lucas DAB125 held in by 2 bolts each with a nut, small spring washer and washer. This unit had a GM amplifier fitted. The bolts have a flat head with two facets that locate into the cutouts on the unit top. The unit then just lifts out.

Here you see how 6 wires are attached to the ignition module- two have internal doubling spades.

I cleaned all terminals and refitted the components. Note that the ignition module has a heat sink via the base so I mounted that with some thermal conductivity grease to make sure it could transmit heat via the base of the unit- taking care to cover only about 1/3 of the base as this is also the earth contact.

The diode is a Lucas LD3520A 16V 35A press fit avalanche diode; 10mm (1/2 inch). Maybe this means more to you? I have found alternatives on sale but usually only at large minimum orders and I haven't yet found anyone who will send a single one or two out. Its press fitted into the box top and its round top surface is visible bottom right in the picture below. I suppose the press fit ensures good thermal conductivity to the top cover although I suspect a few fins here would help too. I was able to verify that the diode was conducting in only one direction so this means the amplifier is probably in good order. I have however ordered a spare Intermotor amplifier unit as  several contributors to the forum have commented on the advisability of keeping a spare to hand!

Note how bolt heads slip into recesses in the case. Diode top bottom right circular structure.