Ok I’m very confused. Here’s the reason why.

With the motor out I though it would be good to clean up some dead wiring that has been hanging around since I bought the car.

The car is a 78. The previous owner had removed the original distributor (electronic) and replaced it with a Lucas 43D4 points model. I subsequently added a Pertronix and a Lucas Sport Coil.

So I wanted to remove the big plug that I guess when to the original distributor and drive resistor. This connector has one wire of white/blue, white/sliver and just white. I get 12v on the white when the key is in the run or start position.

So the Ballast wire (pink/white) is still connected to the starter relay. There is a white/yellow wire on the + side of the coil. There is a white/yellow wire connected to the same point on the starter relay as the Ballast wire. That all seems to match the diagram.

So here where I’m lost. I have 12v at the coil in run and start on the white/yellow wire. If I disconnect the ballast wire and the white/yellow at the starter relay I still get 12v on the coil. Does this mean I’m still using the ballast wire?

If so I’ve been running my pertronix and my sport coil off it for 15 years!

If this is the case it seems like I should be able to cut the ballast wire off and connect the +side of the coil to the white that fed the driver resistor right?

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1978 Triumph Spitfire

My 76 is wired a bit differently but that's similar to what I did. I used the white wire from the drive resistor and connected it to a ballast resistor then to the coil. I eliminated the pink wire. On my car the white to pink connection was in the wiring harness near the alternator.

Looking at the 78 diagram it looks like the pink wire feeds the white yellow wire then goes to the coil. The white yellow get 12 volts from the solenoid only when starting. If you have 12 volts all the time, something must be rewired.

I would have to say no because you said you're getting 12 volts at the coil all the time.
Did you meter it or are you assuming it's 12 volts looking at the diagram. I only ask that because the white yellow should only get power from the solenoid when starting the car.

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"In this world, you must be oh so smart, or oh so pleasant. Well, for years I was smart. I recommend pleasant." Elwood P. Dowd

Yes I did meter it. Still beeing in the shop working on it since the post.

I’m thinking the way they did the 78 was that during starting the white/yellow got 12 volts from the starter relay. Once the car starts the terminal at the relay goes dead and the white yellow draws power through the ballast wire effectively increasing the resistance.

The part I’m stuck on is would you see 12v at the coil either way? I’m thinking yes because adding resistance doesn’t change the voltage just ups the current draw but I might be wrong about that.

I also did some resistance checks. The white/yellow wire has (basically) 0 ohm. The white drive wire to the white/yellow at the coil has 1.8 ohm. Since the only way I can see the coil is powering I think it’s via the ballast wire...

The coil has 3.0 ohms across it. Does this mean the coil has a total draw of 4.8ohm? If so I’m surprised this hasn’t caused problems.

Sorry about the long posts.

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1978 Triumph Spitfire

You will only read 6v at the + side of the coil when the - side is grounded.

If you are going to a 12v system you should ignore everything and tap any white wire for power.

Here are two pictures I made to illustrate the hookup on the Lucas AB-14 in both 6v and 12v.

Our ignition systems are actually quite easy to understand if you take a few minutes to run through it.

Identifying where all your wires go or don't go is a great first step.

Understanding how the ballast wire gets incorporated into the process is a good next step.

This may help you better understand your system and to know what you should keep and what you should get rid of.

http://stevew10.wixsite.com/spit16/ballast-wire-system

All the best.

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Steve
http://stevew10.wix.com/spit16

Andrew,
You can keep the ballasted ignition system. All you need to do is supply the red wire of the Pertronix from that white wire. The black of the Pertronix still goes to the coil negative and the yellow/white from the starter relay still supplies the coil positive.
All the best,
Paul

Series curcuit :voltage is dropped across the resistance. Current remains the same.

Parallel curcuit: voltage remains the same for all branch's.
The current changes or splits off into the branch's. It will follow the path of least resistance.

Your ing system is a switched series curcuit. If your coil is indeed a 3ohm coil the ballast wire should be defeated.
It's starts ok? Because the coil recieives the right amount of power.

Add the total amount of resistance in the series curcuit to obtain the amount of current. 12v/4.8=2.5 amps.
12v/3=3amps. You want that missing .5 amps I think!

Most basic answer I can muster at 6am.



Edited 1 time(s). Last edit at 2018-04-16 06:08 AM by lef2wander.

Thanks guys.

Steve your diagram shows exactly what I was trying to describe.

James, what you said makes sense. Since it’s in series would the volt drop be measurable when the cars not running?

That’s the part that still confuses me is how when I hook my meter from the negative battery to the positive terminal on the coil I get 12v.

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1978 Triumph Spitfire

Hook your meter from the W/Y to the + at coil.

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'S all for now
Vic

The coil will show its maxium supplied voltage. That's why some older style EI systems burn out if the key is left on to long.



Edited 1 time(s). Last edit at 2018-04-16 07:22 AM by lef2wander.

I read through more carefully this time; I think you've got everything correct Andrew.

From your first post...."If this is the case it seems like I should be able to cut the ballast wire off and connect the +side of the coil to the white that fed the driver resistor right?" I'd say yes and that's exactly how I did mine.

From your second.... "The part I’m stuck on is would you see 12v at the coil either way? I’m thinking yes because adding resistance doesn’t change the voltage just ups the current draw but I might be wrong about that." I think you are also correct about that.

and correct about this too...."I also did some resistance checks. The white/yellow wire has (basically) 0 ohm. The white drive wire to the white/yellow at the coil has 1.8 ohm. Since the only way I can see the coil is powering I think it’s via the ballast wire... "

Sounds like you've done some great investigation on this and I imagine you've accounted for all the wires connected to your coil, but what I don't get is why when you disconnect the ballast wire and the white/yellow at the starter relay you are still getting any voltage at the coil? Unless they are remaining connected to each other where you pulled them off.
Other than that there either must be another 12V wire to your coil, or, perhaps a PO spliced 12V into one of those wires someplace you can't see it?

Not sure if that helps.

Edit: typo

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Steve
http://stevew10.wix.com/spit16



Edited 1 time(s). Last edit at 2018-04-17 08:28 PM by Manana.

IMHO... Manana ISteve) is the "go to" source for this particular electrical issue..... He got my 78 Spit running perfectly with my new pertronix system....

Pay attention to him.... or Pay to replace more ignition parts somewhere down the road....

Z

It actually helps quite a bit I think. You are correct I forgot to mention that they ballast wire and the white/yellow are connected to the same female spade so when I disconnected the female spade from the starter relay they are still tied together. To test to see if the PO had modified the wiring all I have to do is separate the ballast wire from the white/yellow and retest at the coil. If I still have 12v then then the PO did some "additional" wiring if not then the system has been running off the ballast wire. If it has, the amazing part is that it has been running this way for 15 years with the Pertonix and a 3ohm coil.

I'll test this later tonight.

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1978 Triumph Spitfire

Hi,
You will measure 12 V on the coil positive with the key in the run position as long as there is no ground to the coil negative. There must be a complete circuit for the ballast to drop the voltage. With no ground the whole rest of the circuit is equivalent to the positive battery terminal as far as voltage goes.
All the best,
Paul

Right Paul. I meant more if after i disconnect the ballast from the white/yellow at the starter relay if I get no voltage then there is no other splices in between the starter relay and the coil.

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1978 Triumph Spitfire