Ignition wiring, ballast wire

[Greenie]

I'm currently restoring a Hurricane and have got to the stage of putting a loom in. I've got 4 different looms to choose from but have opted for one from a Spitfire 1500, based on condition and one or two other factors.

The car is largely based on a MkIII Spitfire with 1300 FD engine, and alternator. I'd already bought a coil for a MkIII and was planning to use that, but I'm a tad confused over the whole issue of ballast resistor and coil.

The wiring diagram in the Haynes manual for the relevant 1500 shows a ballast wire running from the coil to the ignition switch.

So, can I use a coil from a MkIII, or do I need a different one, if so, what? Or should I replace the ballast wire with ordinary wire?

Also, are there any different types of starter solenoids? I have a new 4ST in my spares which I was going to use, is this going to be the right one for the job?

Thanks

[Richard_M]

Hi Greenie

In simple terms, just replace the ballast wire with normal.

Ballast wires are for use with a 6v coil, and drop the voltage from 12v to 6v. This system was used to create a spark boost on cranking for some GT6s and Spits, but not mk3 Spits.

If you've got a 12v coil (standard to mk3) just swap the wire.

R

[Greenie]

Thanks Richard. Is there any merit in keeping the ballast wire and changing the coil? Or would I need to make other changes as well?

[Richard_M]

No real merit, just added complication. I'm not sure why Triumph did this back in the day, maybe they had a load of 6v coils to shift, or maybe they were having starting issues due to plugs/points or whatever - dunno.
I can kind of see it on a 6-pot, where there's more mass for the starter to turn and therefore a quick start is preferred, but even then....

If you had a 6v coil then taking either route would be understandable. As you have a 12v coil and a mk3 based Hurricane - go 12v and no ballast wire - IMHO.

R

[Clive]

There is a big upside to the  ballasted system. The coil will get approx 8 volts (it should run on 6) when cranking, so will give a nice fat spark when it needs it most.
The 12V coil will also get 8V at cranking, so a reduced spark.

However, the extra grief can outweigh the advantage, and leccy ingnition usually needs a 12V supply too. Hence the popularity of dumping the ballast resistor/wire.

[junkuser]

As Clive has said, the voltage available to the coil can drop significantly due to the load of the starter motor whilst cranking, so supplying higher voltage to the coil during cranking is worthwhile.
The amount of voltage drop depends on things like battery condition, ambient temperature, effective engine compression, condition of the wiring etc.

The solenoid to be used with this system must have a connection that will feed battery voltage to the coil whilst cranking. i.e. a bypass for the resistor or resistance wire.

Setting it up so either type coil can be used by simply re-plugging the connections is something worth considering, so you can use any coil you can get hold of if coil fails away from home.
( I believe anything man makes will break down, juust a matter of when)

[Greenie]

Thanks for the help and advice. I'll be adding electronic ignition later so I've ditched the pink and white resistive wire and snipped it back near the coil in case I want to use it at a later date.

I see in the wiring diagram that the pink and white wire at the ignition switch provides the feed for the radio. The pink and white ballast wire seems to join a bunch of white wires a little way back, so if I connect my new wire between the coil and the ignition switch terminal where the white is connected, I should be good to go I guess?

[Clive]

yep, white wires are ignition controlled 12V. I suspect  the pink/white on the ignition switch is just a normal 12V feed, that can be switched on with the ignition off. Nothing to do with the coil.