Dizzy replacement/coil - Ballast or non ballast resistor?

[ricky8664]

Once I've fitted the SD1 heads I want to replace the dizzy with an electronic one as the dwell angle has always wandered (apparently common on early dizzies). However, the options seems to suggest ballast resistor or non ballast resistor options need to be chosen (or maybe wired differently).

My 1971 P5B saloon originally had a coil with an armoured cable cover that ran to the ignition switch  mounted on the L/H side of the steering column. I replaced the coil in the 1980s but when fitting the new coil, the engine would only run for 10 mins before cutting out. Leave it 10 mins and it would run again but for only 10 mins. Took the coil back and they said you needed the other type. However, 40 years later I cannot recall what the "other type" was and therefore, whether the correct coil was ballast or non ballast resistor. Cannot see anything obvious on the coil identifying its type.

BTW, if relevant, the wire from ignition switch to coil has nothing connected to it in between and was replaced by me when I did the new coil back in he 1980s, so not sure if a resistor wire was previously fitted inside the armoured cable.

So what is the correct type or were both types fitted? 

The engine is running fine BTW so I only need the info for the new electronic dizzy type.

[Phil Nottingham]

The later cars had no ballast with the TP coil so there will be no solenoid bypass wiring or terminal on on the solenoid to wire a ballast. A 12v Lucas HA12 or Lucas Sports coil should work and the dizzy will be the later modified version. There will be no resistive ballast wire in the loom so wire the coil direct to the unfused IGNITION feed on the fuse box.

[djm16]

"Sports coil" is shorthand for "low resistance".

With lower resistance comes higher primary current, and more heating in the electronics (and earlier failure).
Check what is the minimum advised primary resistance for your electronic system.

If you want to deviate from standard, then my preference is for iridium tipped plugs. My experience is that starting is easier than with standard plugs. (Plus they last longer).

[enigmas]

If fitting an electronic ignition module then it may save you a lot of grief if you read the following link first.

roverp5.proboards.com/thread/12437/electronic-ignition

[Sam Bee]

I have kept my original dizzy but installed a Pertonix !! unit, externally you cannot tell the difference, except that the dwell adjuster is missing But a plus is that it varies the the dwell angle according to optimum at any one time. It is paired with a Pertronix coil to match. I took the metal sheath off the white wire from the ignition switch and replaced it with a piece of hose the same OD, then simply connected the white wire directly to the coil. Cars with the anti-thief arrangement did not have a ballast resistor or wire. I fitted stainless steel cored plug leads as copper should not be used and I do not like carbon fibre type. Finally, you may have to have your tacho modified internally to work with this arangement.

Photo of mine:

Attachment Deleted

[dmaxwell]

I have used Pertronix distributors on all my cars. They are easy to fit, no special wiring, just one to 12V and the other to the coil. It helps that they are based in the Los Angeles area so shipping is overnight!

David
California