Thanks @classic kev, that's useful info to know. I haven't had a chance to get back on it but the LT wiring is definitely where Im headed next.

Today conspired against me spending much time on this today but I finally managed to get outside at about 5pm. I did the following (which included restarting the car after each step):

1. Started the car. Car started fine.
   
2. Replaced the rotor arm with the red simonbbc one. Car started fine afterwards.
3. Replaced the distributor cap with the new simonbbc one. Car started fine afterwards.
4. Tweaked the timing by ear (I'll do that properly when this is finally sorted). Car ran fine and started fine after.
5. Decided too clean up the coil lT connectors. Removed the -ve side, cleaned up, greased, replaced. CAR DID NOT BLOODY WELL START

That was as far as I got. It now won't start again. On the plus side I guess this does support the view that the problem is in the LT wiring somewhere.

If I earth the king lead and dab the ignition +ve feed on and off the coil +ve, I get a spark at the king lead. So whilst the coil *might* be running slightly high resistance, it would seem the basic LT/HT element of the system is working.

So, wiring-wise, I have:

• Switched 12v from ignition switch to coil +ve, connected to...
• ...Switched 12v from coil +ve to ECU (part of the installation of the 14CUX and the wiring required, iirc it was just somewhere convenient to take the live feed from)
• Blue & red between the distributor and the amp
• White/White & Black from the amp to the +ve and -ve of the coil (poss the other way around with the cable colours!)
• Small/fine black and white from the coil -ve which I believe drives the RPM signal to the ECU. It splits into two and connects to a pair of resistors (the possibly-infamous Lucas 953066 which other websites have had much debate about) and then to two blue & white cables. It's related to the ECU feed to calculate RPM from the coil. I don't think that would be affecting starting, unless the ECU is throwing a fit at not seeing it.

I'm doing this from memory earlier this afternoon but I think that's all of them?

In amongst that little loom which has the resistors in it is also a thin black cable with a female spade connector. This has never been connected all the time the car ever ran properly and I don't know what it is. Possibly an addition earth, but as I say, has never been needed for the car to run.

I'm going to pull the coil and amp out of the car next so that I can get to them better (because it's a modded transplant from a Disco, the coil and the bracket with the amp are sitting down on the inner wing in the general direction of the NS headlight, so not that easy to get to in situ). I'll ring out all those LT connections and see what we get next.

Please feel free to chastise me on any errors in the above approach! (With alternatives!!).

If it was fine until you fiddled with the LT wire I'm inclined to think there's a break or bad connection in the LT wire.

Yes I think that has to be it. It's certainly the next thing to target.

New plugs and leads turned up today but they can wait until it's at least running again.

Cappo said:

So tonight's update........So I stuck the plug lead back on, it fired up immediately and revs cleanly. This is on the original cap and arm, not the new simonbbc ones. I'm dreading even thinking about fitting those again, that's what got me into this mess.....

Click to expand...

Probably not the cause of your erratic start-up but I found the Powerspark cap was a very tight fit. Getting it seated down enough the secure the clips was much harder than usual.

Ratae said:

If it was fine until you fiddled with the LT wire I'm inclined to think there's a break or bad connection in the LT wire.

Click to expand...

That was the problem in my 110, knackered wire in the LT circuit.

Update time: today was the first time I had a chance to have another go at it.

First things first. Bear in mind that I walked away last time because it wouldn't start.......so I put the key in, turned it, and it immediately fired into life. It hasn't been touched since it last would NOT start.

So I thought, right, I'm going to check all the LT leads anyway. Went through them all, with an Avo meter, wiggled them, twisted them, moved them, and all of them showed a full circuit with no breaks anywhere. Cleaned everything up, put it all back together with dielectric grease, and - you guessed, the sodding thing wouldn't start. Still won't. It's definitely all put back correctly, not only did I check everything but the spades are different on either side and it would be difficult to get it wrong.

So I'm back to square 1 yet again. I think I'm going to order a coil, amp, and the remote amp extension lead and just replace the lot and see then - then, everything except the distributor itself will be new. If it plays up after that, then just don't let me anywhere near it when I've got a box of matches in my pocket......

Frustrating.
Did/does the coil get hot? Perhaps the voltage you read from it suggests it's playing up? The ign amp is my next bet, they can be erratic when failing.
As above, the 110s problem was a semi break in one of the wires to the ign amp; would start sometimes not others and could conk out when running.

I once had a nth-hand factory 90 V8; when it went it was marvellous but it had a habit of doing the above, just wouldn't start or would then wouldn't later. It seemed worse when MrsC was driving it or just in it. We christened it "Christine" after the Steven King book and film. Never found out what the problem was as I sold it for the 110.

Good luck.

Thanks @capo . On the previous page you posted a coil and a remote amp kit - as far as I can see the remote amp kit will give me the lead which connects the amp to the distributor (as well as a new amp)? For a few quid more they include the cable to the coil, so I think that has to be my next step, swap all that out and see what happens next.

I had similar but changed the coil and ignition module first and still wouldnt start. Tested all the LT wiring and joints with a meter and all tested fine, in desperation I replaced every spade connector and it fired straight up and has done every time since.

Well I've ordered the parts from Simon now, some of them are pre-terminated but I'll need to put new spades on the wires between the amp and the coil, so everything will be up to full spec - let's see what happens!

One of the wires that goes through the resistors sends a signal to the ecu and its only 5v. I am convinced it was a bad connection on these try cleaning the terminals on the resistors and renewing all four spade connectors

Have also done those already! (There are two on mine, alongside each other, don’t know why).

I know they’re the RPM signal to the ECU but is that a critical prerequisite for it to run?

Yes if the ecu doesn't get a signal the injectors won't fire.

@Cappo
[Columbo voice] Just one more thing... [/Columbo voice]
You say it won't start but do you mean the engine turns over but won't fire up or nothing at all when keying the ignition?
I ask because sometime ago the exciter feed to the starter solenoid had slipped off the terminal so when I turned the key nothing happened apart from the fuel pump running. If your engine turns over then it's obviously not that.

@capo - it turns over fine (well, it did until the repeated attempts to start it started to flatten the battery!) but it just doesn't fire up. Or sometimes does!

Waiting on the new bits turning up now before I have another crack at it.

It's time for an update, as I know you've all been sitting on the edge of your seats waiting

Initially things were somewhat infuriating. If I left the car overnight, it would always start first time, but if I let it run for a minute or two then turned it off, it wouldn't restart. At all. It would flatten the battery rather than start even when it had been running 10 seconds earlier. A rendezvous with Messrs Swan & Vesta was starting to look like a real possibility.... (I'm joking. I think....).

So today I got another chance to have at it. Once again, started immediately and then wouldn't. So I thought I would start changing things out one by one rather than chuck everything at it and not know what worked. Coil first. New one fitted, but still nada, wouldn't start.

On to the ignition amp and the rest of the LT wiring. I ordered the full house from simonbbc. When it turned up, the cable between the amp and the distributor was very different from mine, so I called Simon's tech support line to ask about that and what my options were. Unfortunately I'd have got a lot more sense if I called the BBC in London. Tech Support chap had obviously got out of bed that morning with his "IDGAF" head on, and the most I could get out of him was "if you connect it up wrong, it'll run but it'll run like a sack of ****" (his actual words). He couldn't, or wouldn't, tell me what were my options for converting my 2-pin connector to theirs. The only thing he could actually advise was that I was unlikely to blow the amp up if it was wrong. So, armed with this helpful advice, and far more helpfully with the fact the the old Lucas amp was actually marked up with + and - on the amp, I deduced what I needed to cut and what to connect it to. Managed that, and lo & behold the thing starts and runs. Repeatedly. The lead from the new amp to the old connector on the distributor is currently made off with crimped bullets but if it continues to work I'll solder and heat-shrink it.

So if this does work then it comes down to either the amp or the wiring/spades etc. Looking back to when I had a 3.9 RRC, I remember now that that was a pig to start at times, until I swapped the amp out, so I'm going to go with that as the root cause.

Still haven't fitted the new HT leads or plugs but again, if it behaves, it can have those as a treat at the weekend.

Thanks again for all the help and suggestions on here, it's been useful and has been a good sounding board and support network as I found my way through this.

I might not be spending too much money with the fabled Simon in future tho given the level of backup they provide.

Probably a bit late, but there's a line drawing in post #8 in this thread that might help make sense of it.
https://www.landyzone.co.uk/land-rover/ignition-amplifier.188081/

Cappo said:

So, armed with this helpful advice, and far more helpfully with the fact the the old Lucas amp was actually marked up with + and - on the amp, I deduced what I needed to cut and what to connect it to. Managed that, and lo & behold the thing starts and runs. Repeatedly. The lead from the new amp to the old connector on the distributor is currently made off with crimped bullets but if it continues to work I'll solder and heat-shrink it.

Click to expand...

Good news
If it is working now is it worth replacing the amp? If it runs correctly and no longer cuts out it suggest it was the cable and not the amp. Get some money back from SimonBBC.
It gets hot down there and the wires do seem to deteriorate over time, at least they did on my former V8 dizzies

Edit - Ignore the above, it's late and I'm going batty

Haha, I got the email with the preview of your reply which didn’t show the strike-through formatting, and was going to apologise for not having explained myself clearly - so it’s not just you!!

Does it still start today?