RobPearce

That's possibly why early EI units had short lifespans 😁 A typical ignition coil has a turns ratio of 100:1 and puts out 30kV HT. While the usual "transformer equations" are inapplicable to ignition coils, that one does apply in the specific case. The magnetic energy built up during the dwell phase is released to both coils, and the voltages track to the turns ratio. If the spark path is good, it may spark (and hence conduct the energy release away) before the HT hits 20kV, in which case the LT side won't reach 200V. If, however, the king lead has been removed, it can go way past that. Ballasted coils may be on the high side for turns ratio and probably don't give as much HT either.

When I built a Maplin EI (booster) kit back in the early 1990s, the power transistor in that was rated for 400V, and was protected by a limiter. That's the type of device I'd expect to see. The ones fitted in the Rover MEMS units of the time were better. Standard reckoning within the industry is that 300V is typical, but HT faults can increase it significantly. It will depend on the coil, and actually may be a little lower on a ballasted system.

As thescrapman said, you have the later (and far more common) "voltage sensing" rev counter. The very early Mk2 PI had a "current sensing" rev counter, which has to be wired in series with the supply to the coil. Those were common at one point but rapidly dropped out of favour as the later type came in. So much so that many people, Accuspark included, it seems, have never heard of them. Incidentally: it's not as low voltage as you may think. If you have a pure booster EI (the type that retains the points but reduces the current in them) then you can't move the tacho to before that, because it would then only see 12V and that's not enough for it to reliably work. They are designed to sense the spike you see on the LT side of the coil, which is a few hundred volts.

Actually it's also adding a direct wire from the white circuit to the coil +ve (the red feed to the EI) which not only bypasses the ballast but also the tacho. I don't know whether That's a drawing that Frenchie did from their wording, or a drawing they sent back to him, but either way it's wrong. The one on the left, with the ballast still in, is right.

Err... what? Sorry, the people who answered your query do not know what they're talking about. That second diagram - the "Accuspark recommendation", if I understand you right - will cause your rev counter not to work. Stick with the drawing on the left, which is the same as my earlier one.

No, you shouldn't, because it's not directly connected to the ignition switch. If you look closely at the WSM diagram, and note my comment about not getting misled by the way it's drawn, the rev counter sits between. I've updated your drawing from earlier: Connecting the white/grey to the EI red might work for testing, but so does direct to battery.

Finally fitted Tessa's headlight surrounds. In keeping with just about every other part of her, they're not a terribly good fit.

As usual, the instructions are too simplistic and only cover the most minimal case. Your last drawing is still the correct one. Accuspark have fitting instructions online with a ballast diagram at the bottom, but that's still not right because it doesn't account for your car's current sensed tacho.

Your drawing on the right is pretty close, and good enough since the minor inaccuracies are in bits you won't be fiddling with. (There's a tacho between the ign switch and the white/grey, but that's all at the dash end and you won't be touching it.)

I'm not sure on the Ignitor II but if it is a closed-loop dwell of any worth then it WILL need to be mated with a new coil, which will probably be a dry type.

No, I don't agree. Most EI units (even those with magnetic or optical pickup) really only replace the mechanical points with a transistor - the dwell is still fixed, and the coil is still designed to safely saturate at low engine speed. Thus it's still very sensitive to battery voltage and would still very definitely benefit from the one thing that ballast resistor is intended for - being bypassed during cranking to give a better spark with a weak battery. The thing that would make the ballast resistor pointless is if you fitted a closed-loop-dwell system, with a low resistance coil of the type used on modern cars, which would fry itself if permanently powered. However, that's getting into MegaJolt territory.

Here's that wiring diagram: Observe at the top, items 8 and 80. Note the WS (white and slate grey) wire between them (and don't get confused by the way it's drawn crossing a white wire right next to the dot - that's not a connection!) This is the main supply feed to the coil, through the current sensed tachometer. The WO (white and orange) wire from the other end of the resistor to the coil (item 9) also connects to the starter solenoid, item 7, to provide a bypass of the resistor while cranking.

Sorry - "+ve" (specifically with the plus sign) is electrical engineer's shorthand for "positive"

That won't help. I actually don't have the Haynes for the 2500, just a Unipart (which is useless) and a reprint of the proper BL dealer WSM, which is the one you want. I'll see if I can scan the page you want later this evening. If the Haynes is like the Unipart, it simply does not have the wiring diagram for your car, only the later ones. That's the coil +ve feed, which (on your model year) is not direct from ignition but rather connects to the rev counter. For diagnostic purposes, you could disconnect that and feed the coil direct from the battery, just until you've got it running, then put it back and, if necessary, fix the reason that's not working.

There were a number of "special tools" used on the production line (and in dealers' workshops) purely because it was quicker and more reliable for an illiterate fitter than using a ruler.

Hmm... not expecting to need one any time soon but I do have a Mk1 Vitesse, so it would be useful for stock. And I will have a reason to be in Bristol at some point, as the lad's at Uni there.

I've done it five times in a Mk3 GT6, once in a TR4(A?), once in a TR7 and once in a Spitfire (and some saloons but...) The GT6 is OK - much better now its propshaft is balanced - but the Spitfire was much more fun. The TR7 was... err... not a positive experience, but then it wasn't as well sorted as Howard's. The TR4, on the other hand, was not mine and was very well sorted and made it look easy.

The semi-sports systems have sometimes been reported as even noisier than the full sports ones. I don't think a GT6 rear box would upset a 1300 much, but the bore is too big and you probably want to find some way to mate it to a thinner main system. You can't fit a full GT6 exhaust anyway because the shape's all wrong at the front.

I always found my Dolomites to have excellent heaters. Better than the big saloons, although they weren't bad. The Herald/Vitesse/Spitfire/GT6 heaters were a waste of space, though.

Yes, it should, but it should NOT be the EI supply wire. Hence my comment that the red wire (EI supply) should go to a proper white.

The problem with the back ones is access. The holes in the sump are too small for the tap (and have reinforcement plates) so that needs to come off, at least. Then the backplate is still in the way for all the tools being used. I'll give it a try, though, as I really don't want to take the engine out.

Is there not a white feed to the inertia switch? That's under-bonnet, if I remember right, so might be easier to tee off.

Today I put some oil in Toby's gearbox (it was, indeed, quite low) then went underneath to see if I could spot a leak. Nothing obvious on the gearbox, but the sump is missing two bolts. Unsurprisingly, it's the two that screw into the rear oil seal housing, and the alloy threads are completely stripped. I've got plenty of 5/16" UNF helicoils but from a brief inspection it looks like at very least a sump off job and quite possibly an engine out.

That white/yellow should be connected to your new black wire (ballast to coil). In fact, the white/yellow has two lucar connectors on it, which are intended to go to the coil and the ballast, thus replacing the new black wire. That plays no part in normal running but assists with starting, so worth doing. I think you may have trouble with the EI's red wire connecting to the white/grey. That's not a true "live" (ignition switched, the white circuit) but instead comes through the tacho. Wiring it like that will upset either the EI unit or the tacho, but I'm not sure which.

Canley list GWP200 for Heralds and round-tail Spitfires. GWP201 is for the six cylinder. GWP128 is listed for Mk4/1500 non-viscous, so I suspect it differs only in having a larger pulley diameter (to suit the alternator setup). They should have the same depth, so the same fan belt alignment.