RESISTANCE WIRE BYPASS

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RESISTANCE WIRE BYPASS

Postby 1972nail » Wed Jan 01, 2014 6:12 pm

Ever had an ignition fault that burnt out your Viva?

I had one such fault back in the '70's but thankfully it only fried the loom. I kept the old loom, here it is.



When it happens it is an instant stopper and your car is dead!

The cause is a resistance wire buried deep within the loom. It's there to provide a reduced voltage supply to the coil when the engine is running. During starting the resistance is bypassed and the coil gets a full 12v. On other makes of cars and earlier HB Vivas a simple ballast resistor is placed at the coil safely out in the open where it can do no harm.

Why bypass the wire?

In my case I want to run an Electronic Ignition system that requires a 12v coil and supply. I also was 'bitten' before by the resistance wire so I want to make my car a bit safer. There are other threads on the forum telling you how to bypass and wire in a ballast resistor, thus retaining the existing resistor type coil.

if you bypass and don't wire in an external resistor you MUST replace the coil with a 12v one. Beware, your cold starting may be sightly impaired.

So why does it burn out?

Well, if there is a short circuit there is no fuse on the circuit so instant overload.

Here's how I bypassed the wire in preparation for fitting Electronic Ignition.

The 'resistance' coil feed runs directly from junction D4 on the bulkhead fuse box - the white wire on the right of the 4 in line.



Just simply swap it to junction D5.



You'll have to pop out the whole red connection from the fuse box and use a small screwdriver to release the 'barb' on the terminal. Reset the barb before pushing the wire back in.

No hacking into the loom required, the resistance wire is still there but it no longer is connected to anything so it can't do any harm.

Happy days - 12v ignition - simple!
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Re: RESISTANCE WIRE BYPASS

Postby HC » Fri Jan 03, 2014 7:58 pm

Hi
How do I know if I have a ballast on my 1159cc HC Viva? I have a 12V coil but there isn't any ballast boxes thing near the coil.
Thanks
Chris
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Re: RESISTANCE WIRE BYPASS

Postby 1972nail » Sat Jan 04, 2014 12:38 am

All HC's have the resisance wire and do not have an external resistor. The original AC Delco coil is designed to run with the resistor and is rated at something like 9v, even though it says 12v on the top. The wire is bypassed while cranking on startup so the coil sees 12v for a short period and therefore you get a fatter spark.

If someone has fitted a 'normal' 12v coil to your car and not bypassed the resistance wire then you will be getting a weak spark during running, particularly at higher revs as the coil won't have enough dwell time to charge fully from the lower voltage before firing.

Also the coil will always be trying to draw a larger current through the resistance wire and it could overheat the wire. That's the problem I had back in the 70's, I fitted a 12v Lucas Sports coil and within a couple of weeks I had a fried loom.......

If you bypass the wire and don't change the coil then the coil will certainly give you a fatter spark all the time but it will die very quickly as it is being overrun constantly.
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Re: RESISTANCE WIRE BYPASS

Postby 1972nail » Sat Jan 04, 2014 1:57 am

You can check if your resistance wire is still in circuit by connecting a Voltmeter to the ignition wire at the coil with the engine running. It will read something in the region of 10 to 11v if the resistance wire is still connected. Once the wire is bypassed as I described it should read about 13 to 14v with the engine running. With the engine stopped and the ignition on (red light illuminated on the dash) it should read 9 and 12v respectfully.
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Re: RESISTANCE WIRE BYPASS

Postby Paul Dawson » Sat Jan 04, 2014 10:01 am

On mine (1972) I have two white wires coming out of D4.

The wiring diagram shows two wires for the earlier ones and a single wire for the later ones.

If I remove both those wires from D4 will that do the same job? Looking at the wiring diagram the connection with the resistance wire seems to be before the fusebox - so if I disconect the wire between D4 and the coil how is the coil still getting a 12v feed?

Sorry - probably a dumb question but electrics aren't my strong point.
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Re: RESISTANCE WIRE BYPASS

Postby 1972nail » Sat Jan 04, 2014 3:26 pm

Paul Dawson wrote:On mine (1972) I have two white wires coming out of D4.

The wiring diagram shows two wires for the earlier ones and a single wire for the later ones.

If I remove both those wires from D4 will that do the same job? Looking at the wiring diagram the connection with the resistance wire seems to be before the fusebox - so if I disconect the wire between D4 and the coil how is the coil still getting a 12v feed?

Sorry - probably a dumb question but electrics aren't my strong point.


You need to remove the connection from D4 and then put it into D5. The new feed to the coil comes from D5.

There are 2 wires connected to D4 on the OHV cars with the inertia type starter. One wire supplies the resistance wire feed to the coil during normal running while the other is the bypass 12v feed connection from the solenoid, only active when starting. There should be no problem swapping both D4 wires to D5.
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Re: RESISTANCE WIRE BYPASS

Postby ShaBro » Wed Jan 15, 2014 1:25 am

I'm just wondering if someone had fitted a 12v coil and not done this, could it be causing my misfire on over run?
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Re: RESISTANCE WIRE BYPASS

Postby 1972nail » Wed Jan 15, 2014 9:04 pm

Could be.... the coil doesn't get enough voltage to charge up and provide a fat spark to ignite the weak 'overrun mixture'.

There is an excellent description of coil types and properties on the Stealth Ignition web site. Is your coil the standard equipment AC coil? If it is it probably is the correct coil. If it is a Lucas coil or a 'Sports' coil then it may be the wrong coil.

Although there are Lucas coils made for resistor ignition circuits. The Green Spark Plug Company has a good section on the different Lucas coils from memory.
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Re: RESISTANCE WIRE BYPASS

Postby Andrew Morris » Sat Apr 19, 2014 6:25 pm

Thanks to all that have posted here. I too am not totally 100% with electrics so here are my findings. Equally I am unsure on a couple of things so forgive me for asking a few questions.

My late 78 HC 1300 viva would not start at all ,so went through everything and decided the only item that needed replacing was the coil. I decided on this as the coil was the only part of the ignition that I had never replaced. So having bought a Lucas 12 v sports coil I then discovered that the HT lead was corroded at the distributor :oops: so replaced the lead. (Always the most obvious thing eh?)

It did eventually start but usually on 5 or 6 turn and then with new 12 v Lucas sports coil fitted the engine started to misfire intermittently at around 45/50 mph.

Then I read this thread ! :o :o so off with the new coil and back on with the old Delco and problem solved and now starts on turn 2 :D Also the car has stopped misfiring too. :D

Now I have also bought one of these Accuspark Electronic Ignition things and to date have not fitted it. Sorry for lack of understanding here but before I start am I to ?

1,Remove the 2 white wires from D4 and re fit into D5 on the fuse board (I have two wires, not one)
2,Fit my Accuspark
3,re fit my 12V new lucas sports coil or keep the old 9/12v Delco on the car.


The thought of losing my loom would finish both myself and the car off :shock:

Thanks in anticipation
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Re: RESISTANCE WIRE BYPASS

Postby Paul Dawson » Sat Apr 19, 2014 6:43 pm

Andrew - I've just fitted the Accuspark kit to my 1972 Viva 1256, using the Lucas 12v 3ohm coil.

As David says, just swap the two wires in D4 to D5, fit your new 12v coil, fit the Accuspark module, then you connect the black lead from the Accuspark to the negative terminal on the coil, the existing white wire (which is now a 12v ignition live) goes on one of the positive connections on the coil and the red lead from the Accuspark goes on the other positive connection.

Just be aware that the +ve and -ve low tension connections on the coil may be reverse to your original coil.

I did mine yesterday and it fired first time.
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