Author Topic: Where is the 'Resistive Wire' in the Bis ignition circuit?  (Read 340 times)

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elanman99

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Where is the 'Resistive Wire' in the Bis ignition circuit?
« on: April 09, 2019, 09:25:33 PM »
Whilst trying to diagnose a poor running watercooled 126 engine I looked in the Workshop Manual CD and on page 13 it give an explanation of how the ignitions circuit works (wasted spark etc) and shows that the circuit is fed by a 'Resistive wire'. The actual wiring diagram on page 23 shows the battery, coil, contact breaker etc but nowhere does it show a resistor (which presumably would be a ballast resistor).

The coil is shown as having two HT connections for the plug leads, and two more on the primary side but these last two are not marked with polarity.

Is there a hidden ballast resistor in a Bis?

Ian


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Gadge

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #1 on: April 10, 2019, 12:37:20 PM »
Personally haven’t it took a few of these apart I’ve never come across one unless it’s hidden somewhere like within the coil or behind a bulkhead.
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dajwid

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #2 on: April 10, 2019, 04:53:20 PM »
I’m really not into the Bis, so May very well be wrong.
Isn’t it in the front under the bonnet hinges.

elanman99

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #3 on: April 10, 2019, 08:20:19 PM »
I’m really not into the Bis, so May very well be wrong.
Isn’t it in the front under the bonnet hinges.

I dont think there is any wiring close to the bonnet hinges so whatever the 'thing' is, that is not shown in the wiring diagram it not there.

Seems odd that it is not shown in the manual so I don't actually know what I am looking for! The only thing I have to go on is the fact that somewhere between the fuse box and the ignition coil I am loosing volts.

This hunt for the invisible and unknown object started because I piggy-backed  the wire feeding the coil (which is supposed to come from the ignition switch) to feed an electric fuel pump. The pump, which is a Facet electronic, one must draw a high-ish current as there is only 5 Volts on the coil. Investigations led me to the 'resistive' wire mention in the manual.

Ian
Located in Sunny Sandiway

ChrisRLewis

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #4 on: April 11, 2019, 08:21:13 AM »
Isn't it the cable itself from the coil to the ignition switch (or fuse box) which acts as the ballast circuit?
« Last Edit: April 12, 2019, 04:21:17 PM by ChrisRLewis »

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Da Londo

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #5 on: April 12, 2019, 11:54:19 AM »
Isn't it the cable itself from the coil to the ignition switch (or fuse box) which is acts as the ballast circuit?

What he said, cable should be resistive.

elanman99

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #6 on: April 12, 2019, 02:04:31 PM »
All wire has resistance.

Usually wire that is used to connect things together, whether its a car loom, a door bell or a supercomputer, is chosen so that its resistance is negligible relative to its function and if resistors are needed they are usually separate items. If the Bis ignition wiring is done with some non-standard resistive wire one would imagine that it would not just have the usual PVC sheath but in some way would be identified or clearly marked. Not putting it in the workshop manual makes it even more mysterious.

The only manual I have is the CD sold on this website, maybe there is other documentation available?

Ian


 
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ChrisRLewis

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #7 on: April 12, 2019, 04:22:47 PM »
Have you tried taking a voltage reading on the low tension circuit, coil to ignition switch?



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elanman99

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #8 on: April 12, 2019, 04:49:12 PM »
I dont have access to the car for a few days so cannot do any measuring yet. However I did measure the volts exactly as shown in that video and measured 12V at the coil, with the contact breaker open which it would, since the meter draws virtually no current. I do not know what the voltage is with the points closed but when I connected the fuel pump the it dropped to less than 6V.

It does seem that there is a ballast resistor somewhere in the car, I just dont know where FSM put it.

Ian
 
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Bar Vitelli

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #9 on: April 12, 2019, 09:33:37 PM »
I’m not an expert on the BIS but found this on another forum which may help:

‘As I recall the ballast resistor on a 126 was situated in the front boot, in the centre at the front. At first I didn't realise what it was (it looks like a large coil of wire with very open turns). Presumably it was sited in the boot to keep it cool.’

Hope it helps.
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Pete126

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #10 on: April 13, 2019, 12:18:29 AM »
This is how my pump is wired in, you have to use a relay if you want to use the ballasted feed on the coil as the drain is minimal, as the voltage drops there's enough power to keep the relay locked in
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elanman99

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Re: Where is the 'Resistive Wire' in the Bis ignition circuit?
« Reply #11 on: April 13, 2019, 09:18:51 AM »
Pete

That's perfect. Two reasons, one that it saves me the trouble of running a dedicated wire from the ignition switch to the pump in the engine compartment (use fused feed off the starter motor) and secondly you confirm that the Bis does actually have a ballasted ignition circuit!

I had come to the conclusion that there must be a ballast resistor but finding it has proved difficult.

Thanks, Ian
Located in Sunny Sandiway