Ballast Resistor

[pwd95]

Getting rid of the ballast resistor & using a suitable coil etc....
The more I read the more it appears not to be needed.

Discuss......

[adam quantrill]

Ahh the mythical ballast resistor.....

[adam quantrill]

What ballast resistor? There isn't one!

[adam quantrill]

Ohh yes there is.... it's that resistance wire in the loom.

Edited by adam quantrill on Friday 6th August 20:09

[adam quantrill]

Prove it! Rover SD1 never had one!!! Grrr.

[adam quantrill]

There you go Wyn, enough discussion for you?

I'm sure there will be more coming along short-ly (sic).

[adam quantrill]

In the mean time as you have the 400SE (same as mine sort of but let's not rub that in) same wiring anyway...

Yes I found there's a few volts drop in the loom and there appears to be a few ohms (not measured exactly yet) in the ignition circuit. We think it's in the form of a blue-sleeved resistance wire in the loom. I did have my dash apart before this ballast resistance debate all kicked off but I don't think I found it, or got a detailed enough photo showing it, but that's the most likely place. I don't think it's in the engine bay.

Why is it in there? You might ask... The best theory I've come up with so far is that:

1. You MUST use a high-output coil on a 400SE
2, BUT the coil is run de-rated (i.e. at less that 12V usually)
3. So you still get a strong enough spark
4. But the coil is running cooler and (my theory goes) therefore the reliability is better.

The de-rating might also help with back EMF from the coil primary which stresses the ignition amplifier, less back EMF, less stress, longer lasting ignition amp.

[pwd95]

Thought this was it...... two in fact connected in series...

[Adrian@]

Is the car running dim dip and using the ballasts to do it, one for each side (red/blue) OR red white two stage dash lights. A@

[adam quantrill]

Yes as Adrian intimates, that's a lighting-related resistor(s) and not for the ignition (you did say coil...) I thought they might be for the instrument lights dimming?

Interestingly though in the photo there's a blue-coloured wire in the background.

[pwd95]

Ah, ok. So I can go ahead & fit a proper coil. Still chasing my stuttering between 3-4k rpm problem...

[adam quantrill]

Well, it really ought to be a high-output coil, as both myself and Keith have measured a less-than-battery coil voltage in our 400's.

If you use a bog standard 12V coil the spark might be a bit weak.

[Hamish400]

Om my 400se I have two ballast resistors in series near the power steering pump on my car. They are wired to a knob / switch under the right hand dash which serves to dim the instrument lights when in one position (bright dashboard lights in the other position)

Regards
Hamish

[pwd95]

Hamish400 said:

Om my 400se I have two ballast resistors in series near the power steering pump on my car. They are wired to a knob / switch under the right hand dash which serves to dim the instrument lights when in one position (bright dashboard lights in the other position)

Regards
Hamish

Looks to be the same thing on mine...

[Pumpkin123]

adam quantrill said:

Well, it really ought to be a high-output coil, as both myself and Keith have measured a less-than-battery coil voltage in our 400's.

If you use a bog standard 12V coil the spark might be a bit weak.

Don't suppose you'd have a link to what coil you are using, I'd be quite interested to see how it compares to mine...

[adam quantrill]

I still have the original one in mine. A while back the garage doing the service thought they'd replace it but luckily kept the original, which went back in. I think it's a Bosch, but will get the part number off it some time. I don't have garages doing services any more - it was too expensive due to preventative maintenance parts swapping!