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In harness resistor for 69 SC?

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ccowx View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ccowx Quote  Post ReplyReply Direct Link To This Post Topic: In harness resistor for 69 SC?
    Posted: Feb/11/2018 at 3:30pm
I am looking at installing the resistor back into a 69 SC/Rambler that has had it removed for an aftermarket ignition system. What is the gauge and length of the wire? Is it simply 14(?) gauge single strand copper wire of whatever length or do I need to know anything else?

Thanks!

Chris
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2018 at 4:02pm
It's not normal wire - it's literally a resistor in wire form, it helps control amperage through the ignition points/coil.
|The only junk harnesses I have on hand to measure from are Javelin and others, otherwise I'd pull a harness apart and measure the length and such. Actually, you could get the resistance wire from a junk harness.......
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2018 at 5:56pm
From the 69 TSN, the resistance wire should be 1.35 ohms for V8, 1.80 for a 6, +/- 0.5 ohm @ 70F
69 Javelin SST BBO 390 T10
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ccowx Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2018 at 6:18pm
I have a junk harness from a 1970 Javelin that may have one, but is it possible to buy new wire?

Thanks!

Chris
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Feb/17/2018 at 2:19pm
Roger Gazur
1969 'B' Scheme SC/Rambler
1970 RWB 4-spd Machine
1970 Sonic Silver auto AMX

All project cars.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SCRAGTOP Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2018 at 8:46am
Yes, you can purchase new resistor wire. There are several sites online which sell the wire. The crucial issue will be length. If you buy a small spool of wire (like 25ft) I would cut a 48 inch(ish) length of wire and put 12v thru it and measure the output voltage. I don't remember the expected voltage value (I am writing this while at work without access to the manuals) but I believe you are looking to get 8 to 10 volts for the points. So, a shorter wire will increase the voltage and a longer wire will lower the voltage.

Experiment with your new wire as each manufacturer probably uses a slightly different method or materials during the manufacturing process which may change the expected resistance value. For example, the factory tech manual may say the resistance wire (from 1969) is supposed to be 60 inches long, but the resistance wire you purchased provides the same voltage drop at 50 inches.

Too much voltage and you decrease the life expectancy of your points, too little voltage and the car won't run or run right. Lastly, most resistor wire for sale that I have seen, comes with gray colored insulation. I would get some yellow Krylon plastic paint and paint it before installing it to give it the correct "look".

Pretty sure I have stated everything correctly but Billd up above is the resident Master Electrician and may have additional or more accurate info.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce Clarkson Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2018 at 3:08pm
Please keep in mind that voltage drop is a function of resistance (related to length) AND the current flow (essentially load). This means to measure the voltage drop you'll need to drive a correct coil to make your measurements.

Alternative: measure the end to end resistance (ohms) of an existing correct wire and trim the new resistor wire to match.

Best of luck,
Bruce Clarkson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Feb/19/2018 at 5:53pm
Bruce is correct, you will be measuring at a specific temperature - because this is how these wires work.
These are current limiting devices - ballast type resistor. They are supposed to control the current more than the voltage into the ignition system. They warm up due to increased load, and gain in resistance lowering the current.

Frankly I'd not over-think this - I'd find a good resistance wire from a good used harness and use that unless I could be sure of matching. 
Unless it's crispy,  not flexible or shows signs of being hot I'd not be afraid of a used one.
Yes you can buy new - sure - but a used one from an AMC _V8_ harness will be ok as long as you get all of it you can - keep the length as much as possible.

Bruce's post nails it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/20/2018 at 8:16am
Don't ever cut resistor wire. It will reduce the resistance of the cable. Since the wire used is spec'd in ohms/foot, you need a specific length of cable to get the desired resistance.

x3 on what Bruce Clarkson said. You can't measure a voltage drop in a no load condition.
69 Javelin SST BBO 390 T10
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Feb/20/2018 at 8:45am
No one here is advocating cutting the resistance wire - only the splices.
And when one considers the original wire is in feet and inches, an eighth of an inch isn't going to change things other than perhaps make up for the increased resistance across old connections LOL
Seriously, I've removed ignition wires from harnesses and used them over in other harnesses. One simply needs to remove the splice and not cut the wire back.
On the end closer to the coil it's typically joined back to yellow at the connection that slips onto the I terminal of the starter solenoid. 
At the most you may lose a quarter inch out of how many inches........... and that won't impact the system more than the plus/minus built in already. We aren't talking critical systems where a fraction will cause an amp to go into oscillations. 
I've done 'em for years and never lost a set of points or coil over it. You just do it carefully to maintain the length of the wire, and keep it within specs. 

Your own statement above shows he's got MORE than enough wiggle room to do this - 

>> 1.35 ohms for V8, 1.80 for a 6, +/- 0.5 ohm @ 70F <<

So what would 1/8" or even 1/4" do for a spec that's 1.35 +/- .5  ?????  1.35 plus or minus .5 means he could chop off a quarter inch and be well within specs. 
That spec is saying 1.35 ideal but 1.85 to at low as .85 is ok.

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