Ballast resistor wire

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Llessur
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Ballast resistor wire

#1 Post by Llessur » Tue May 22, 2018 10:28 am

My car, a 1977 2500S, has a pink and white wire which joins to the wire from the positive terminal of the coil and then runs as part of the loom in through the grommet above the passenger footwell. I'm not sure where it goes from there.

The wire is showing signs of having overheated - the insultation is quite badly damaged and melted. Looking at my other car, a 1975 TC, it is showing exactly the same problem.

Having looked back through some old posts I think this is a resitive wire which was fitted as an alternative to a separate ballast resistor. Obviously it is prone to breaking down seeing as both my cars exhibit the same problem.

I'm not particularly electrically-minded so can anyone explain what the options are for fixing this issue i.e.

a) if I replace the wire where does it go and does it need to be a particular gauge to maintain the correct level of resistance?
b) would it be easier to fit a separate ballast resistor and do away with this wire altogether? If so, what is needed here?
c) any other suggestions?

Thanks all!
Adelaide, South Australia
1975 2500 - Murky silver
1977 2500S - White

My blog: https://triumph2500blog.wordpress.com/

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Alec
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Re: Ballast resistor wire

#2 Post by Alec » Tue May 22, 2018 12:05 pm

Hello llessur,

I've never had a car new enough to have the resistive wire, but you would need to get the correct wire to replace it. I don't know whethetr they are available any longer, but I believe it's incorporated in the loom and is fed from the ignition switch. There is or should be another wire from teh starter motor and that also connects to the positive terminal on the coil.
The idea being that when the starter is operated, the battery voltage drops due to the load, the wire from the starter motor bypasses the resistor and gives full battery voltage to the coil. The coil is not a 12v coil (although I've seen some ballast coils marked 12 v) but 6 v which is why in normal running the 12 voltage is dropped down by the resistor to give 6 volts (or about that) to the coil This is designed to give a boost to the gnition while starting the engine. With a normal system, when the car starts and the battery voltage drops the coil doesn't give maximum output due to a reduced voltage. With the Triumph system the drop in battery voltage feeds teh coil which gets at least the 6 or so volts it needs, maybe more so giving full voltage to teh plugs. Quite clever really.
Your options depend on what spares are available? and your inclination. The car will work quite well with a normal wire instead of the resistive wire but you must change the coil for a 12 volt one or it will probably burn out.

P.S. if the wire is sound and it's only the insulation, you could just sleeve it with glassfibre sleeving? That might be the easiest and cheapest solution?

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.
Jaguar X Type Estate 2.5

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Llessur
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Re: Ballast resistor wire

#3 Post by Llessur » Tue May 22, 2018 12:32 pm

Cheers Alec, the wire is part of the main loom so is wrapped in black tape behind the dash - resleeving wouldn't be an easy option.

That leaves me with either keeping the same setup with a new wire or changing the setup as per your message.

My worry about keeping the existing setup is that this wire is obviously prone to overheating and I'd be worried about a potential fire risk.

So could I run a new standard wire from wherever this pink & white wire connects to the ignition switch through to the coil and fit an external ballast resistor in that, thus keeping the 6v coil?

Also, is this wire cooking a symptom of a problem somewhere in the system, or just bad design?
Adelaide, South Australia
1975 2500 - Murky silver
1977 2500S - White

My blog: https://triumph2500blog.wordpress.com/

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Alec
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Re: Ballast resistor wire

#4 Post by Alec » Tue May 22, 2018 8:59 pm

Hello Lessur,

it is inevitable that it will get hot so it is not a sign of other problems.

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.
Jaguar X Type Estate 2.5

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Llessur
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Re: Ballast resistor wire

#5 Post by Llessur » Wed May 23, 2018 4:27 am

I've done a bit of reading up on this and it seems that possibly the easiest fix is to do away with the ballasted system altogether and fit a 12v coil. My understanding is that the ballasted system was introduced to make cold starting easier - but seeing as I live in a relatively warm climate hopefully that won't be too much of an issue.

My plan of action would be to:

1) Remove the entire section of burnt resistance wire and replace it with regular 12 gauge wire (white). I think this feeds from the white ignition-switched circuit at the fuse box but I will need to do some poking around to confirm.
2) Change the coil to a 12v one and connect the new wire to the + terminal together with the existing feed from the starter solenoid.
3) Have a nice cup of tea and a bit of a sit down.

Can anyone spot any flaws in this plan? Anything I need to be particularly aware of? Is 12 gauge wire OK? Any coil recommendations? What sort of biscuits should I have with my tea?
Adelaide, South Australia
1975 2500 - Murky silver
1977 2500S - White

My blog: https://triumph2500blog.wordpress.com/

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Alec
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Re: Ballast resistor wire

#6 Post by Alec » Wed May 23, 2018 5:57 am

Hello llessur,

just remove the wire from the starter to the coil (or disconnect and tape up the ends.) as it will no longer be needed.
I'm not familiar with gauge as a wire size, but it is not a heavy current requirement.

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.
Jaguar X Type Estate 2.5

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Llessur
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Re: Ballast resistor wire

#7 Post by Llessur » Wed May 23, 2018 6:31 am

Cheers Alec,

Just to confirm - the starter feed is not required in addition to the switched feed from the ignition circuit? Is the ignition circuit live when cranking in that case?
Adelaide, South Australia
1975 2500 - Murky silver
1977 2500S - White

My blog: https://triumph2500blog.wordpress.com/

User avatar
Alec
Senior Member
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Posts: 2308
Joined: Sat Feb 07, 2004 7:23 pm
Location: Oswestry, Shropshire

Re: Ballast resistor wire

#8 Post by Alec » Wed May 23, 2018 12:21 pm

Hello Llessur,

Ye the ignition feed is live when cranking.

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.
Jaguar X Type Estate 2.5

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