Hello all,

I've been trying to sort out the intermittent no start on my Series III, and I think I've figured out the problem. I've got no spark coming out of the coil, and I think I know why. I'm only reading ~7.5V across the coil poles, even when reading directly across the leads unplugged from the coil. I'm also reading ~0.1V across the amplifier leads when disconnected from the coil. The coil itself reads fine, with ~1 Ohm across the poles and 9.5K Ohms from the positive to secondary winding. I tried this with two different batteries, one of which was freshly charged. The voltage across the battery leads with the first, lower, battery was ~11.5V, and I expect the fresh battery would have produced closer to 12V.

I've been reading the wiring diagrams, and I can't figure out where the coil is getting its current from. The diagram confusingly shows three leads coming into and out of the amplifier, when there are only two on mine. Further, the wiring diagram shows three leads coming off the ballast resistor, when mine had only two (I replaced the old coil and resistor a year ago with an internally resisted coil). Further still, the diagram shows only one lead coming off the positive of the coil, when mine has two. This diagram actually contradicts another diagram in the same part of the manual, which shows the two lead-per-pole setup my coil has. As such, I'm no closer to understanding where to start looking to find the cause of this low voltage.

As always, looking for advice on the matter.

 

Two wire Ignition amplifier

Intermittent ignition can come from: 1. Distributor pickup 2. GM module in the amplifier 3. Ignition Coil 4. Ignition switch , or the wires in between each unit.
Jaguar XJ6 S3:
1. C to (-) terminal of Ignition Coil = White with black stiped wire
2. B to (+) terminal of Ignition Coil = White wire
3. IGN SW to (+) terminal of Coil = Brown (or White) wire
4. EFI to (-) terminal of Ignition Coil = White with Black wire
5. Tach to (-) terminal of Ignition Coil = Slate with Blue spiral stripe wire

GM module will be intermittent when hot, before a complete fail. In the Lucas Ignition amplifier there is a "Radio Interference Capacitor" and a Current Fault Diode, neither is required for ignition and both can short to ground causing ignition failure. When you have a no start situation, unhook both inside the Amplifier for T/S.

Ignition switch is age related. Forum members have disassembled, cleaned and lubed electrical portion of Ignition switch. You can buy electrical portion only, from usual sources.
Distributor and Ignition amplifier need good grounds. The ground (in picture) on the ignition Amplifier mounting bolt, doesn't have to go to Battery ground post, any good grounding point on engine is ok.

It is a process of elimination to find where the fault is.
Rgds
David