Good day all,
My ignition switch was acting up a couple of months back. Checked spark when in the “Start” detent of the switch and nothing. Bring the switch to “Ignition” and down to “Accessory.” The coil would spark just between Ignition and Accessory positions in the key, but not when on “Start.” To me, that’s entirely switch related. With some searching, I found it’s a pretty easily serviceable part. I removed the switch, found years of corrosion and degradation within the assembly, cleaned it, reassembled, reinstalled and bam, problem solved!

That was the case for about two flawless weeks when I suddenly had the same problem again. Thankfully, both times have been in my garage before I take the car out. So rather than tempting fate, bought a switch off of SNG, part number DAC1422. As SNG doesn’t have support for the SII on their website, it looked like it was the same switch from the E-type and on from Moss and a few other sources. Minor differences between the switch I received and what I had, but wiring was the same. Plugged in the new switch and back up and running.

Until today. Took the car off my car lift to spin it around to work on right hand u-joints, did some rearranging before getting the car back on the lift, and then nothing. Pulled the coil lead off the distributor, near ground, crank and no spark. But I would get the spark between the two ignition and accessory detents in the switch. Pulled the new switch apart and found more noticeable differences internally, but perfectly clean. Reassembled and still the issue persists.

For kicks and giggles, went around to check voltages at the coil and ballast resistor. Everything checks according to the manual, however, I did find resistance to be slightly high on two of the three internal resistors. I’m on the hunt for a new ballast resistor (unless there is advice for replacing with a different unit or omitting it entirely, wisdom and wiring help here?) but I don’t think the 0.4ohms over spec on the 2nd and 3rd internal resistor is enough to cause a problem. I haven’t bypassed the resistor yet by running a jumper from the battery to the + of the coil, but I may soon, at least to get the car in the correct position.

I should note, I have removed the original reed switch from the distributor and replaced it with the Hall effect pickup, the Trigger Board Kit from SNG, p/n: AEU1683.
I don’t see this change interfering in any way, but it does require tapping into the “SW” ignition switch wire going into the ballast resistor.

Electrical is not my strong suit, but this car and my new-to-me XJS is forcing my hand here. I don’t know what else the problem could be except for the switch? I’m thinking that the ballast resistor is getting just warm enough, creating more resistance internally, and being the weak spot. I would think there should be more inconsistent symptoms over time then just outright stopping. The fact I get a spark between the ignition and accessory detents really just screams mechanical fault to me, but I’m at a loss. I can’t find my original ignition switch, I don’t think I tossed it, but it’s possible as it’s not in my spares section of the garage. Frustrating.

 

I had a similar problem with my Series III ignition switch, only it was intermittently losing the feed to the ignition circuit when in the run position, rather than the start position.

I bought a new switch from Martin Robey but after fitting it, the problem was not resolved.

I then realised that the replacement switch had some detail differences from the original. The new switch lacked a hole for the locking grubscrew, so came loose. I drilled a hole to solve that but still had intermittent problems. Then I noticed that the hexagonal keyway in the new switch lacked a central tongue, so the drive dog on the steering lock operated by the key was not gripping firmly. It was slipping and so allowing the switch to lose position 2 and revert to position 1, thus killing the ignition

pics show old and new switches and the drive dog of the steering lock






I then modified the new switch by gluing in a tongue made of hard plastic to match the original. This seems to have resolved the problem

 

Mine is missing this tang as well. What I’m currently testing, however, is the switch outside of the ignition cylinder. A torx T30 or T27 (can’t remember which) fits perfectly in the hole to manipulate and create consistent pressure when turning the switch. I thought it might be pressure related as well, but since I can apply good pressure with the t-handle torx, I don’t think that’s the issue. Something I did just think about, however, is that the housing of the switch assembly isn’t grounded itself. I’ve started the car with the switch out before, but don’t remember if I added a ground since it’s not contacting anything. I still get a spark between Ignition and Accessory, though, even with the switch removed from the steering column.

 

I found that, without the tang in the middle of the switch, the drive dog in the steering column lock tended to close up and therefore not mate well with the ignition switch. That is to say, the slot closed up so the dog became reduced in size and so not a snug fit into the ignition switch

 

Some tie back, I had weird issues. A NOS ignition switch via mDavid boger of everydayxj fixed the issues.

I took my old switch aart. Mistake. Parts flew everywhere. should have worked over a pa or better, in a bag. The old switch was sloppy loose. Teh Ns nice and snug.

Too many keys on the key ring and many years...
Carl

 

I am actuating the switch outside of the assembly though, entirely away from the steering column.

I reconnected the purple-black ground wire that grounds itself under the key this morning, and the bloody car started! A good night's rest for the car and I helped, I'm sure. While it was running, I decided to back it out and get it on the lift. I revved the engine a bit to excite the alternator (I'll address that eventually) and the car died...on the downhill slope...with a lot of pushing and clever usage of a ratchet strap, I got it back inside. Fiddled with wiring to see if there is a break anywhere and couldn't detect anything. The switch is still in the "ignition" position, the coil energized, the ballast resistor getting warmer, etc. Tried it again and the car started. Again, the ignition switch is completely removed and using a t-handle torx to actuate the switch. While the car was running this time, I disconnected the purple-black wire because I don't know what I'm doing and the car still ran fine, so it can't be that simple ground. I don't see how it could the the plastic tang in the switch body when it's removed from the key tumbler.

 

I found the issue!
It actually had to do with the ignition update I had done, the AEU1683 kit. It ended up being my shoddy soldering job when providing the trigger board 12v. What ended up happening was my solder joint connecting to the provided bullet connectors was just garbage, the wire had frayed away on the 12v supply to the ballast resistor, which disconnected power to the trigger board. I found it weird that I had a spark when the key would change positions, but not when cranking. Finally figured it was a trigger issue, and sure enough, started pulling on wires and the power to the trigger board just popped right off the bullet connector tee that was fitted. Oh well