OK, I admit it, I'm kind of an electrical *****, sometimes. I've looked through google and did a search on here, without finding the info I need. Oh, yeah, the car is OT, but the info might be helpful with someone re-wiring a rod or custom. (There, I THINK I covered all the bases to prevent a simple question from turning into a **** storm, but some of the guys on here never cease to amaze me........) The resistor wire in my wife's OT, 12v car is shot (only getting about 3½v between the battery + post and the coil + post with the ignition switch in the "Run" position. I'd like to convert the set-up to a ballast resistor, since it'd be easier to change if it goes bad a long way from home. My shop manual says the stock resistor wire is 1.35 ohms, so I went on line and found a 1.35 Ohm resistor out of a '66 Chevy is also 1.35 Ohms, so I bought it. So far, so good. The stock wire in the car, running from the ignition switch to the firewall connector, is 12awg (plain electrical wire). The stock resistor wire, from the firewall connector to the coil, is a 20awg wire. Maybe I'm over thinking it, but I want to make sure I'm not screwing this up (it's my wife's car, after all) - Should I be running 12awg wire to the ballast resistor, then run 20 awg from the ballast resistor to the coil or should that wire be larger, since it's not a resistor, but is post resistor ?? What size should I be using. Or doesn't size matter ?? Thanks for your help, -Bob
I'd use #16 wire, it's about the right size for what you're doing I'm a bit confused about what you think is wrong with the original resistor wire. If the voltage is too low, that indicates to me that perhaps the coil has too low of resistance on it's primary side...???? is it the original coil?
You lost me - 3 1/2v BETWEEN the battery + and Coil + ????? Do you mean 3 1/2v difference between the two readings? You should be checking voltage using the coil + and ground - is that what you are doing? And that is how you are getting 3 1/2v? And have you checked it with the car running?
Sorry, should have been clearer. The initial problem was that the car shut down once in a while, but got worse rapidly until the engine would start in the "Start" position, but shut down every time the key was released into the "Run" position. That led me to check the voltage through the resistor wire to the coil, which I did by disconnecting the wire at the coil + terminal, and checking the voltage between the battery + terminal position and the end of the resistor wire with the ignition switch in the "Run" and it was only 3½v. I think it's supposed to be around 7-9. When I checked the other, non-resistor wire, going to the coil + terminal (again, not connected to the coil for the test), with the ignition switch in the "Start" position, I get a full 12v, which should be correct......I think. ***uming the above info is correct, I was questioning why the OEM wiring was 12awg to the firewall, but only 20awg resistance wire to the coil. It just seemed odd to me that they'd use large wire halfway, then change to a much smaller wire - perhaps to reduce any resistance from the switch to the firewall connector wire, which may affect the resistance in the resistor wire? Man, I'm even confusing myself, now........ Thanks for your patience. I was a little frustrated when I started the thread. -Bob
Run the test again, but with the 20 ga wire connected to the coil. Now check for voltage (key in 'run' pos.) at where the 12 ga. wire terminates at the 20 ga. More voltage at the 12 ga. wire? If so, attach the ballast resistor and as Jim suggested, run a 16 ga, wire to the coil, attaching with alligator clip. Start and run, recheck volts at coil +. Then tell us, please.
Resistor wire is made by a calculation of the resistivity of the material times the length divided by the area. So to get the drop they needed (To about 9v as you guesses) the area (diameter) of the wire will be smaller than the wire that feeds the power to it. It also builds heat and I would imagine they went a little over board on the wire ga. feeding it both for safety and to be sure that it was getting a good steady current.
Might want to check the wire terminals carefully at the firewall connector, perhaps they are corroded or dirty or something. But yeah, the resistor wire is small, because it's a resistor.
Have you checked the voltage at the output (ign) side of the switch? Sometimes switch contacts develop considerable resistance over time. It seems to me low voltage coming from the switch would exacerbate the voltage drop through the resistor wire, even if is in good condition. You may find you have 12+ volts across the switch, but at least you'll know it isn't part of the problem. Ray
Ray, New switch was installed with no change and getting a full 12v, but thanks for your suggestion. -Bob
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