Spitfire Spitfire Ignition Wiring - Story with followup ?'s

[pipercollins]

This will be a more or less familiar story to many of you...a wicked combination of Lucas electrics and previous owner muddling.

So Monday evening was the monthly British Motoring Club cruise night. I hadn't been real regular at club meetings for the last year or two (house renovation). But I'd had a little more time recently to tweak some things with the 1976 1500. I had the carb tuned up and did some suspension work and everything had been running pretty good. The weather was perfect, so I was looking forward to the drive.

The group took off with 10 or 12 cars and all is well, until 10 minutes into the scenic cruise, the Spit dies. I see the tach go to zero. I'm rolling down a hill at this point, in the middle of our pack. So I down shift and pop the clutch. The engine whines while I keep slowing down, but it doesn't catch. No ignition. I roll around the corner through a busy intersection and wheel over to the side of the road. A couple of the other club members stop with me while everyone else goes on.

We pop the hood and look around. All the connections look good. Distributor, plugs, and wires are all about a year old. I'd had a similar symptom earlier in the spring and had to replace the cable from the battery to the starter solenoid...that was definitely good now. Nothing obvious, but it's definitely no ignition. Now, the PO had installed a Jacobs ignition control computer. A little blue box mounted to the frame, supposed to "condition" the spark. I've always been skeptical of its value, but I hadn't gotten around to the very involved job of rewiring everythign to eliminate it. It does change the wiring between the coil, the distributor, and the drive resistor. It also incorporated a switch in-line in the computer's wiring harness so you can run it on "computer" or "conv ignition". (I've run it both ways, never noticing a difference...)

That switch always makes people scratch their heads, but it's always worked. Till now, anyway. One of the other guys fiddled with the switch while I tried to start the car. We actually got it to fire a couple of times, but couldn't get it to keep going. So it seemed to me that switch was the culprit. Of course, parked alongside the road in fading daylight, one looks for direction and reassurance. My buddies seemed to agree with me, but very noncommitally. Fair enough. My car. It's up to me. Fortunately, I've owned a Triumph long enough to know what to keep in the boot. Wire pliers, connectors, and a reel of jumper wire, among other things. Unfortunately, the ignition computer invalidated the laminated wiring diagram.

OK. Man of action. Disconnect the battery (thank you, quick disconnect). Take a deep breath. Cut the switch out. Reconnect all four wires straight, eliminating the switch. Reconnect the batter (thank you, quick disconnect). Start the car (it fired up immediately). Back on the road in about 12 minutes. Everyone else beat us to the pub, but we got there before the first round of drinks. I was briefly embarrassed, but my street cred (literally) remained intact. Not bad for a Monday.

I got home fine and everything, but now I'm left wondering how best to make my quick fix permanent. I'm inclined to go ahead and eliminate the ignition computer, but that means some pretty involved rewiring. I'll post more as I sort through it, but does anyone have any from-the-hip insights on original ignition configurations vs. ignition computers and "spark conditioning"?

Regards all,
Bill

 

[Roger]

First off, I think you have maligned Joe Lucas. By the sound of it, you didn't have a Lucas problem but a Jacobs problem.

Second, if you're not convinced about Jacobs, go ahead and re-wire. You may want to replace the coil if the PO went the whole way and put in a Jacobs coil. BTW, what is the "Drive resistor"? It's a term I don't know - is it part of the Jacobs setup?

Anyway, rewiring to standard is easy. One wire to coil from ignition switch, one from coil to distributor. Does your distributor still have standard points and condenser? If not, get them too.

 

[pipercollins]

Thanks for the input, Roger.

I did not intend to malign Mr. Lucas...or at least not directly. But the combination of Lucas wiring with PO muddling makes troubleshooting even harder than otherwise. And I would submit that there was a Lucas problem before the PO made it better, or indeed, worse.

Looking at the standard wiring diagram and sketching out an as-wired diagram, I think I can eliminate the Jacobs system and rewire it as original for the most part. But here are a few more details/questions:

1. I've got the 45DE4 "electronic" distributor. (So no points to worry about.)

2. Original spec calls for a ballast resistor wire btwn the coil (+) and the drive resistor/switch lead. (Not a ballast resistor brick, but a wire with the correct resistance.) No such wire is in place now. The car apparently got a Jacobs 0.6 ohm coil when the computer was installed, so I'm guessing that's why the ballast wire was clipped. So if I eliminate the Jacobs computer, do I also need to change out the coil for an original spec 1.3-1.45 ohm version? Or am I OK as long as I don't add a ballast wire?

3. The "Drive Resistor" was original equipment, stated purpose "to function as an essential requirement of the amplifier transistors." It gets a scant mention in the shop manual. The wiring diagram has it wired in parallel between the distributor and the key switch. My drive resistor is clearly an aftermarket one. I don't know whether it went along with the Jacobs unit, or if it was a replacement for a dead OEM resistor at some other point. (My hunch is the latter.) It has a red wire that goes to the key (and spliced to a red wire for the Jacobs), a black wire that goes to the tach (also spliced to black for the Jacobs), and 3-wire pigtail that connects via Lucas connector to a similar 3-wire pigtail from the distributor. There are no other wires leading from the distributor.

You can spend a lot of time reading up on this stuff...

Bill

 

[pipercollins]

Here's a slightly blurry pic of the Drive Resistor.


2011 08 18 001 by pipercollins, on Flickr

 

[71MKIV]

a coil is a coil is a coil, The only difference is that a 6 volt coil, one you have to have a resistor inline when the switch is in run, starts on 12 volts, so things are a little hotter during startup.

If it's a 12volt coil and it works keep it.

Put the wires back the way they were and be thankful the snake oil box didn't fry that expensive distributor.

I think that box is just a poor mans capacative discharge ignition system. Good ones are expensive. cheape ones are ineffective.

 

[pipercollins]

OK, here's what I tried over the weekend.

I cut the Jacobs "computer" out of the system, but I kept the drive resistor/amplifier/conditioner whateverthehell that thing on the firewall is. I would entertain eliminating it, but it connects to the dizzy with a 3-wire cable that is clearly manufacturer-built to go between the two devices.

However, without the Jacobs computer it does't run right. It will run, but it starts hard. When I drive it, it will cut in and out (lose the tach completely when it cuts out). It seems to cut out under heavy load/acceleration, but it's not really consistent. So I rewired it again with the computer back in for the time being and it drives fine again. (As long as my connections are all tight.)

So...
As far as I can tell, my 45DE4 distributor is the factory original. (I've only replaced the cap and rotor a couple years ago.) It connects to that box on the firewall by an apparent factory connector, so if that's not an original installation, I wouldn't know it. I did read something somewhere about problems with the 45DE4 dizzy in the very beginning and dealer-installed enhancements/replacements on brand new cars...maybe that's what this is? So maybe original to the car, but not OEM equipment in the shop manual?

Still seeking more understanding of what I've got. If I really have the desire to "simplify" the ignition system and make it more original (by the book) it seems I actually have to buy more stuff...

 

[70herald]

I think that there are a few ways to go about this.

1. Find parts for the original. Lucas system - good luck.

2. get the parts needed to put point and a condenser into the distributor. Points work well, are reliable and will do the job. However, if your distributor originally was built for electronic it may not be so easy to convert, for example if the shaft doesn't have lobes on it to open the points, this is not going to be easy.

3. get a "points to electronic ignition conversion kit" such as either the Crane xr700 or Pertronix, and a new coil (if needed) Then get rid of everything and put the new system in.

I personally have the Crane XR700 in the Herald driving a standard coil and it works just fine. As long as the distributor is in good shape this should basically a drop in operation. There is a sensor put into the distributor, a small control box, with wires to power the coil, power and ground. It shouldn't take more than an hour to install.

 

[KSIS]

That thingy on the firewall is the Old Allison ignition unit. I run the same on my Spit and TR6. I would look at rotating or adjusting the electric eye under your dizzy cap.

 

[pipercollins]

That thingy on the firewall is the Old Allison ignition unit. I run the same on my Spit and TR6. I would look at rotating or adjusting the electric eye under your dizzy cap.

Hmmm... OK, thank you for identifying that piece for me. Now I can at least relate it to other things I've read.

I'll have to read up on adjusting the electric eye in the dizzy, now. Hope to have some more play time this weekend.

 

[KSIS]

The wiring/ adjusting will be the same as the XR700. Also check the wiring for any breaks. I had this issue. The car would sputter. I'll send a PM.

 

[dklawson]

And don't get the module on the firewall wet. That's how I killed my Allison unit when washing the GT6 engine.

 

[pipercollins]

Thanks guys. Especially for the notes, KSIS.

I'll look forward to getting into it this weekend.

 

[pipercollins]

Thank you all, especially KSIS. I now have the Jacobs "computer" removed and the car is purring along fine.

It was helpful to resolve the question that the Allison unit actually belongs there. Now it's wired more or less per spec. Loosening the dizzy clamp and turning it 3 or 4 degrees cleared the timing up nicely. It wasn't hard at all once someone knowledgable pointed me in the right direction.

Hey, one more follow up question: I'm now (and have been) using a 12v Jacobs coil, so no ballast resistor. And it was set up that way whenever that "computer" was installed. Everything works great right now without the computer in the mix, but I've read different things and I'm a little foggy about the 12v vs 6v coils. I believe I'm OK with the 12v and no resistor wire. Is that all there is to it? Or should I be worried about something slowly and steadily getting fried if I don't go back to the original 6v coil and ballast resistor?

The PO had a mechanic who really seems to have overcomplicated things when he didn't know how to get British parts. I've had to redo ignition, fuel pump, horn, radio speaker, etc. etc. All those jobs were done before with new parts that didn't fit the car. Jeeze, it's not that hard to get the right parts in the internet age...

 

[71MKIV]

Should be fine.
the only issue is to make sure that a 12 volt coil is installed when that one poops out.

It's when it 's the other way around, a 6 volt coil in with no resistor that it takes it's time and fails at the worst possible moment.

 

[dklawson]

I don't know what a Jacobs Coil is so I cannot comment about it specifically.

If you have gone back to points you can use a multimeter to measure the components you have and confirm they are matched. The tests are simple.

1) Mark and remove the wires for the coil low tension terminals. Set your multimeter to measure resistance and measure across the coil's low tension terminals.

2) Place the wires back on the coil. Remove the distributor cap and place a coin between the contact points. Set your meter up to measure volts. Turn the ignition on and measure the voltage between the coil (+) terminal (the one NOT connected to the distributor) and a ground point on the engine block.

If you measured about 3 Ohms on the coil, you have a "standard ignition" or 12V coil. If you measured 1-2 Ohms, you have a ballast coil that needs ballast coil wiring.

If during the voltage measurements you found 12V on coil (+) you have "standard ignition" wiring and you need a 12V coil. If you measured 6-9 volts, you have a ballast ignition system and you need a ballast coil.

You can run a 12V coil on a ballast ignition system but the spark will be weak and you may have running/driving problems. If you put a ballast coil in a standard ignition system, too much current will flow through the components. This causes premature failure of the points and sometimes the coil.