Back to basics with Mk4 Spitfire ignition

[Dougieboard]

Hello all. I recently joined the club and have been working my way through the forum which I have found very informative!

I am hoping for a few pointers with regard to my recently acquired project - I don't think I have seen the exact query raised previously but apologies if this is recovering old ground.

I have an early Mk4 Spitfire and it is fair to say it has been mucked about with. I didn't pay a huge amount for it, but that was because it had some known issues. By which I mean, I know it has issues but not necessarily how to solve them!

The first thing I need to get to the bottom of is the ignition set-up.

What I know

• I know the car has previously had electronic ignition.
• Due to running issues, it was reverted to standard points ignition again.
• At the same time, it has been fitted with a new distributor.   
• It's not the right one. It has no mechanical drive for the rev counter. 
• I bought it with the current owner telling me that 'it will only run if you connect power from the starter solenoid directly to the coil' Yuk. 

My limited knowledge of ignition systems and reading of the forum leads me to think that I probably have some combination of ignition components that are not compatible with one another. Perhaps the wrong coil, definitely the wrong dizzy. Rather than just replacing bits though, I'd like to work out what is going on. And then, inevitably, start replacing bits. 

So I think my questions are:

1/ How can I tell what output/rating the coil is that is fitted to the car?

2/ The wiring in my car does not appear to match the Haynes manual - but whether the manual is correct, the car is correct or neither is correct, I am not sure. Is there an easy to way to work out whether or not my car has / should have a ballast resistor set-up?

3/ This will be a weekend car - used for the odd show and pootling around. Should I aim to restore the original function or is an electronic ignition set-up just good sense? 

Any pointers, queries or questions equally appreciated! Thanks for reading

 

Edited July 3, 2022 by Dougieboard
typo

[RobPearce]

Hello Doug, welcome to the forum.

While you definitely have the wrong distributor and quite possibly the wrong coil, the problem you describe is not because of either of them, so don't go worrying about them yet.

Does the car run properly if you connect a wire from battery to coil, as the PO said? If so, the problem is with the wiring or the ignition switch - there's really not much else there in the bit you're bypassing. As it's a Mk4 then it would originally have had a ballast resistor system, with a large ceramic resistor probably bolted to the coil fixings. However, the PO who fitted electronic ignition may have replaced the coil with a non-ballast one.

What connections do you have on the coil? Please post a photo. If it's a ballasted coil, there should be two wires on the + terminal (or maybe one wire that goes to the resistor then into the loom), just the one to the distributor on the - terminal. For non-ballast, it's one wire on +, which should be white.

Do you have a multimeter? If not, get one. You'll need it.

One more question for now: without the bypass wire, i.e. just the car as it is, does it start at all? In particular, does it start and run until you release the ignition key from the crank position? That's a common symptom of some common faults.

[Dougieboard]

Thanks for the response. 

Please see enclosed pic - the red cable is the temporary one needed to make it start - that just connects to the crocodile clip that is clipped on it - this is the temporary cable.

With that cable clipped to the starter solenoid, it runs fine, apart from you need to get out of the car, pop the bonnet and disconnect it to stop the engine as you might expect. 

I do have a multimeter! 

And I shall have run a test tomorrow to see what happens with an attempted start without the crutch of the extra cable. I recall the PO said it just span over and never fired, but I'll confirm this and come back to you.

Many thanks 

[RobPearce]

Interesting. I take it the white wire from the other coil terminal goes to the distributor? It shouldn't really be white but if that's what emerges from the points then so be it. The green wire that shares with the red is definitely wrong - that one should be white, and I think I'd expect it to come from the bit of loom that feeds the solenoid. The green wire from the lower part of the loom should go to the gearbox, for reversing lights and overdrive (if fitted). There's a white/yellow wire floating loose in the top right of the picture, which I suspect is the coil feed via the ballast resistor.

So:

- do your reversing lights work?

- do the minor gauges and indicators work?

[Dougieboard]

Again, thanks for the reply.

Righto - the white wire does indeed go to the distributor - it is joined by spade connector to a black wire before if goes through the distributor grommet. 

The green wire does emerge from the loom low down. (see pic) Sadly, it is a non-od model so nothing to check there. And the grubby white-yellow wire tucked under the fuse-box has a couple of unused terminals on it. 

I will check the status of the reversing lights, but as per the picture, I can confirm fuel and temp gauges work. (Headlamp switch is on the todo list!)

I've had a look at the coil which looks new, but suspiciously free of any branding or useful info to indicate spec.

Thanks!

[RobPearce]

OK, the gauge check was just as a side-note, wondering whether (if that green wire is the one it looks like) the fuse had blown. However, it occurs to me that with the red wire present the check isn't actually reliable.

It would be worth doing a couple of multimeter checks, both with the coil disconnected:

- measure the resistance of the coil primary (between the terminals). If it's about 3 ohm then it's a non-ballast coil; if it's 1.5 ohm then it's a ballast type. This will determine how you need to re-wire it.

- with ignition on, measure the voltage from that green wire to ground (engine block should be a good ground, or battery negative). If you can (an assistant helps), check that for all four ignition switch positions.

Edited July 4, 2022 by RobPearce
After-thought

[Dougieboard]

Dusted off the multimeter. 

• Coil is bang on 3.0ohms
• Ignition on - the green cable shows 0V for the three first positions, and around 5V when cranking. No assistance available as the dog was asleep and the other half was at work. Involved balancing the meter on the wiper, but I soldiered on...

I have confirmed that without the red link wire clipped on, the engine cranks and spins over happily but will not fire. When the link wire is attached, it fires instantly, but won't turn off with the key, as you might expect. 

Really appreciate the responses, btw. Thanks

[RobPearce]

36 minutes ago, Dougieboard said:

Ignition on - the green cable shows 0V for the three first positions, and around 5V when cranking.

Hmm... that's very strange. A green in the loom ought to be fused-ignition-switched and should be at 12V for positions three and four. A blown fuse would give nothing on any position. The only wires that should be "live" on crank only are the white/red that connects to the solenoid and (if otherwise disconnected) the ballast resistor bypass from the other solenoid small terminal - which is probably the white/yellow that's dangling free. And, of course, they should both go to battery volts, not just 5V.

Is there, by any chance, a stray white wire emerging from the loom near the coil, probably fairly close to the white/yellow? If so, that's likely to be the one that should connect to the coil instead of the green wire.

[Dougieboard]

Nothing coming out of the loom low down other than the oil pressure sender wire.

I am a bit suspicious of how heavily re-taped the loom is, the fact that the colour is not what you'd expect and the red crimp-on spade connector. I will see if I can trace the wire at all to get a few more clues - it feels like a repair or modification of some sort.

I will ask the other half to help me confirm the 5V reading on crank too. Will report back soon!

Thanks again

Edited July 4, 2022 by Dougieboard

[RobPearce]

1 hour ago, Dougieboard said:

Nothing coming out of the loom low down other than the oil pressure sender wire.

No, not low down. The feed to the coil is supposed to emerge from the higher up part where the solenoid connections and the unconnected white/yellow are. The lower section is supposed to sprout a pair (one green and one green/brown) for the reverse light switch, then pass down to the chassis, sprout the oil pressure wire, then branch the alternator and temperature sender bundle, and so on. No ignition bits in there.

As you say, it does look like there's been some bodgery going on.

[Dougieboard]

Ok. I've confirmed that the green wire shows 5V when cranking, but nothing the rest of the time. Not sure what it is connected to but it goes into the loom and without cutting the wrap off it, I can't tell more. It doesn't look too mucked about with though, aside from the red terminal. 

Further down, alongside the engine, there is a brown/white wire going to the oil pressure switch. No evidence of a reverse light wire that I can see. 

Looking at the loom, there is a white wire as you suggested - only a couple of inches long, right next to the fuse box with a spade connector. This is not connected to anything.

The longer yellow/white wire comes out in around the same spot, high-up with two spade connectors on it and is not connected to anything either.  I connected the yellow white wire to the coil in place of the green wire - the engine fired but wouldn't run - cutting out as soon as the ignition was released from the cranking position. The yellow/white wire shows around 10V when cranking. 

Based on what you said about the short white wire, is it worth making up a short patch cable and hooking it up? Feels like it might be worth a go!

 

Thanks

 

[RobPearce]

9 hours ago, Dougieboard said:

Based on what you said about the short white wire, is it worth making up a short patch cable and hooking it up? Feels like it might be worth a go!

Definitely worth a go. The behaviour you got with the white/yellow is exactly what I'd expect if it's the ballast bypass as I guessed. If the short white is a couple of inches short of the white/yellow then that's where the ballast resistor would have gone and that white wire is the one you want.

[Dougieboard]

Hurrah!

Please see image. Horrible red crocodile clip wire repurposed to bridge between the white wire and the coil, with the green cable left disconnected.

Result was an immediate start on the key, and the car turns off on the key too. Nice! I'll now clean and tidy up that little corner and make up something a little less awful looking to bridge the gap between the coil and white wire. 

Only thing is that with the green wire disconnected from the coil, there is now no turn signals or fuel gauge. Putting power to the green wire makes both work. Final questions and I'll leave you in peace

• Any idea what the green wire should be connected to?

Huge thanks for helping we unpick this all. My club membership has already paid for itself!

 

[RobPearce]

37 minutes ago, Dougieboard said:

Any idea what the green wire should be connected to?

I rather suspect it's the feed for the reversing light switch, and the reason it has the effect you observe is that the fuse has blown (or isn't making a good connection, which is extremely common). As I mentioned earlier, ALL plain green wires in the original loom are fused-ignition-switched-supply. This supply feeds the reversing light circuit, the indicator circuit, the fuel and temperature gauges (via a regulator), the brake lights and the wipers.

So your next step, with that green wire still disconnected, should be to check the fuses with your multimeter, identify which one connects the white circuit to the green circuit, and make sure it's providing continuity. With ignition off, multimeter set to ohms, check between that green wire and each end of each of the fuses. If you get continuity only to one end of one fuse, double check that the other end of that fuse has continuity to the white wire, then replace that fuse and you should be good to go.

[Dougieboard]

Righto. I followed all the instructions above and it turns out that a perfectly good looking fuse in the top position of the fusebox was in fact, a dud.

The PO hooking the green wire up to the coil had restored function to things (presumably back to front!), so I will pick up some new fuses, clean up the fusebox connections and earths, and I hope we are back to a functioning car! 

Many thanks for all the help. I'm sure it won't be the last time!

Edited July 6, 2022 by Dougieboard