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hammered Offline
#1 Posted : Wednesday, 10 January 2018 3:11:15 PM(UTC)
hammered

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Checking out the wiring under the dash of my old holden.Is there a table or graph available to help determine if wires are still servicable?Each time I use the multimeter,I'm never sure if resistance is too high,so take a guess.Was told once that 9000 ohms/foot is about maximum for spark plug leads.That's about all I know.
Dr Terry Offline
#2 Posted : Wednesday, 10 January 2018 3:50:18 PM(UTC)
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Most spark plug leads are resistive, so 10K per foot is a good average, but the rest of wiring in the car is copper so its resistance should be negligible.

Also copper doesn't age as such. Old wiring in cars suffers from age in 2 ways. Firstly the crimped ends can corrode, leading to bad connections & secondly the insulation will crumble, meaning it no longer 'insulates' & can cause short circuits.

I've used many old wiring harnesses once they pass a good close visual inspection. Any corroded terminals can be re-terminated, but if there are too many & the plastic insulation is too far gone, then get another one. You can be lucky sometimes by obtaining a good 2nd hand one which requires few if any repairs, or you could buy a new one or have one made from scratch.

Dr Terry
If at first you don't succeed, just call it Version 1.0
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#3 Posted : Thursday, 11 January 2018 10:52:47 AM(UTC)
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There is a company called Vintage Wiring in Ringwood Victoria. Their website is Vinwire.com.au. They can often advise on problems and offer repaired or replacement harnesses. Unfortunately for some models they have to use your existing end clips or plugs. However the end result is a product that seems to satisfy most restorations.
johnperth Offline
#4 Posted : Saturday, 13 January 2018 4:35:53 PM(UTC)
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As Terry says most wiring apart from the spark plugs will have practically no resistance. if it does, look for a bad connection somewhere.
Behind the dash the only wire with resistance is found on pre-electronic ignition cars and that is the pink wire to the distributor, it has resistance to cut the power from around 12 volts down to around 9 volts to protect the points and condenser.
KBM Offline
#5 Posted : Saturday, 13 January 2018 5:59:12 PM(UTC)
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Actually johnperth your not quite correct there. the yellow wire from the ignition switch to the firewall connector runs at 12v during startup and then drops in voltage, while the motor is running in the on position, via a resistance wire which is white with orange and violet cross traces. it's resistance is 18 +/- .05 ohms. the pink wire behind the dash is 12v power wire to the ignition switch. that's the way it's for HK,T,G i'm not sure on the colours in earlier/later pre electronic ignition models but the circuits are the same.
Dr Terry Offline
#6 Posted : Sunday, 14 January 2018 8:33:54 AM(UTC)
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KBM, the colours are different for different series. A white/orange/violet ballast wire was used in EH to HG, this changed to pink for HQ onwards.

The by-pass wire was pink in EH, but changed to yellow for HD-HZ.

Dr Terry
If at first you don't succeed, just call it Version 1.0
KBM Offline
#7 Posted : Sunday, 14 January 2018 12:03:26 PM(UTC)
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ok, looks like I was wrong about the pink not being able to be the by-pass wire so my apologies johnperth.
thanks for the details Dr Terry.
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#8 Posted : Sunday, 14 January 2018 8:52:27 PM(UTC)
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Don't sweat it mate, I learnt something also..
regards,
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