Good day all,
After many struggles, I've rebuilt the ignition harness, cleaned up the valley, changed intake gaskets, installed a new ballast resistor, and retrofitted the later square fuel rail to my pre-HE V12. I replaced the female molex locking spade connectors into the ballast resistor connectors to keep the original aesthetic, and I still have issues where I lose connection between the new resistor and the original 4-hole plastic connectors on both sides of the ballast resistor. I'm not terribly fond of using standard shielded connectors for the ballast resistor just due to the proximity of metal around the ballast resistor, but I'm getting to that point because as this car warms up after a few minutes, I lose spark until everything cools down and the metal shrinks again, making contact. I had this exact issue with a direct coil on a 2006 Saab I had. It's a simple, but really annoying issue.

At some point, the previous owner bypassed the tach/negative coil wire that goes through the top connections of the ballast resistor with some kind of in-line resistor, part number: Lucas RD 953066. There are still two terminals being used on the ballast resistor currently, bottom and middle. Electrical theory is not my strong suit in any way, so I'm really flying blind here. I understand that an internally resistant coil could help eliminate this whole setup, but one of the leads goes to the ignition amp above the radiator, correct? I'd be concerned about not having something in line for that connection. Is there any guidance out there for a way to replace this Lucas 9BR 47246A with a unit with ring terminals or just any other ideas? I'm tired of fighting this thing.

 

Further diagnosis:
I have been disconnecting the lead from the coil to the distributor, and allowing the distributor side to discharge on ground. When everything functions correctly, I get a spark when the key is turned to the "Run" position, when cranking, and when I turn the key away from "Run," there is another discharge. When the system is not functioning, I only have a spark when I turn the key off of run, no spark when I first turn the key to run and obviously not when cranking.

I added a ground to the 5-wire ignition amplifier body just for good measure. I noted that the ignition amp grounds to the radiator upper support, if I unscrew it from there and isolate it, no spark occurs at any time. I feel the added ground to the amplifier body is extra insurance. I removed the red/black wire (Middle "E" post) and the white/black (Bottom "F" post) from the factory connector and made sure the ballast resistor is making good contact to these two wires. I further removed the distributor cap and adjusted the ignition pickup closer to the trigger wheel. Still no result.

Because I still get a spark when I turn the key off, I'm theorizing the ignition amp is not the culprit. I'm thinking it may be the trigger pickup, wiring to and from the pickup to the 3-wire connector, the 3-wire connector to the amplifier itself, or the two wires from the ballast resistor to the amp. I noticed there are screws on the base of the amp, so it gives the appearance it can be opened. There may be a broken wire somewhere in line, so I'll be stripping back the wire protection and see if there is anything obvious.

 

I would stop playing with the cables and check the resistances of the ballast to be sure if it is working or not. The workshop manual tells the correct values and how it should be connected. My experience is that it does not get intermittent contact with heat or any spade contacts, original or not. The Opus amplifier however is famous for being unreliable and often works when cold but cuts out or misfires when hot. I was running my car with external resistors when waiting for parts. The amplifier my dad diagnosed as having a faulty semiconductor which we replaced with one from mum’s washing machine. This was almost 30 years ago and it is still running fine. SNG Barratt have rebuilt ignition systems but they cost a bit.
I remember two occasions having the same behaviour with only one spark when turning off the ignition. One resistance was burnt off, it happened first start after powerwashing the engine..

 

I verified resistances on the new ballast resistor and attempted to use my original resistor as well throughout this process, though the original one is slightly out of tolerance. Still can’t isolate the issue.

I found an old Crane Cams XR700 kit for the V12 and will be going that route. This is my wife’s car and I really can’t leave the possibility of her being stranded. A bit of a rich comment for these cars, but this is the last standing issue from this cars resurrection. Put on over 1000 miles last year with virtually no issues.

 

Before leaving for work this morning, I tested spark by trying the key and turning the car over. The ignition was sparking. I did nothing other than reach through the window opening and turn the key, so I think that really narrows it down to the amplifier. Disappointing...I'll open it up and see what is going on later, but I think I'll be happy with the XR700 in the end. Just need to figure out a mounting bracket for the pickup as I see in a few places the included bracket leaves much to be desired.

 

Good, I believe you are right. What you can try when you miss the spark is to spray cooling spray (buy cheap in normal spray can) on the suspicious parts. This would help understand what is going on.

 

I should have used compressed air last night as well. The annoying thing is the system should have been cold last night. My issues started at around 1700, didn't touch it until just before bed at around 2200. 5 hours with the bonnet open is a pretty long time to cool down. Odd that 8 hours would? Oh well. Hopefully this thread serves others along the way in some manner.