The Stovebolt Site Forums The Shop Area The Electrical Bay distributor aand ignition coil question

I replaced myignition coil on my 67 Chevy PU. parts store sold me a coil that says 'use with external resistor only'. old coil did not say this. I don't think the truck has an external resistor. It's a 12volt system. How do i check this. did the parts store sell me the correct coil? i do have what looks like an extra condensor mounted to the coil bracket which is wired to the negative coil terminal? What's this?
The distributor already has a condensor mounted as one piece with the points.
Anyway, I am trying to trouble shoot a no spark situation. I drove the truck into the garage to
do a tuneup. I replaced the distributor cap,
rotor, plugs and couldn't start the truck to set tthe dwell after doing this. Trouble shooting revealed no spark from the coil. Replaced the coil and now I have voltage at the coil but still have no spark. I plan to run the distributor checks ssuggested by race carl in a previous thread but I still have questions about the coil?
Any help would be appreciated.

Check the voltage at you coil, if there is a resistor somwhere, you should have about 9v on the + terminal. there should not be an extra capactor on the - side of the coil, + side ok radio noise supression. With the cap off check for voltage on the - side while opening and closing the points, if this changes you should have spark, unless the points are set too close.

hestor - the lack of external or internal resistance will just fry the points in time, but shouldn't stop it from starting

sounds just as likely that the coil was not the problem [if the truck ran B4 ya started in on it] and that you got the wrong coil - can't recall for sure, but I don't think that series truck had ignition resistor any more - the "extra condensor" you note on the coil is for radio noise suppression [even if ya don't have a radio!]

back to checkin yer work!! cap on rite? wires in the right place? remember to put the rotor in? points set rite?

Bill

Our trucks ran a resistor wire instead of a ballast resistor. It's actually the wire that runs from the firewall to the positive side of the coil. I the coil should get full 12 volts when cranking, but it will drop back down to 9 volts or so when running. You can use the coil you bought, ust leave the resistor wire in place.

Did you remove the distributor at any point? What did you set the point gap at? How does the engine sound when trying to crank it over? Any and all details would be great. If you have a voltmeter, then just check your system for open circuits. I hope this helps some. John.
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As previosly mentioned, GM used a resistor wire instead of an external resistor. Turn key on and check for voltage at coil. 7-9 volts indicates that you have resistence. If voltage is higher, points will burn.
A thought: Do you still have the resistor bypass wire on the (+) side of the coil? You should have 2 wires on (+) side, one from the key, one from the starter. If not, it is possible that you are getting little to no voltage at coil during cranking.
The wire from the starter should come off the solenoid terminal marked "R".

Just a thought here on checking the voltage at the coil. You will only get a voltage drop from the resistor when there is current flowing through the circuit, that is, when the points are closed. When the points are open, you will have the full 12 volts regardless of whether you have a ballast resistor(or resistance feed wire) or not. Check those points also to make sure they are grounded on one side(and only one side). If they aren't, you aren't going to get any spark out of the coil.

Thanks for the info on the coil and points. This is what I know so far:
I have 12v at the coil with the ignition switch on.
There are two wires on the positive side of the coil. One runs back to the starter, the other through the firewall to the ignition switch.
The coil I relaced was not the trucks original coil and I always seem to go through points quickly.
I plan to check out the points as you all suggested and I'll let you know in a day or so what I find.
Also, I haven't had the distributor out.
Thanks,
hestor

Concerning the wires on the + side of the coil; the wire that goes back through the firewall is your main feed to the coil. The wire to the starter is meant to feed the full 12 volts to the coil during cranking. The presence of this "bypass" wire means that the other wire through the firewall should have some resistance to it to knock the voltage to the coil down somewhere in the range of 6 to 9 volts. This is done either with a ballast resistor, or the wire itself having the neccesary resistance. Turn the ignition on and measure the voltage at the + side of the coil with the points closed. If you have more than 9 volts there, this is why your points don't last. Now open the points and measure the voltage at the + side of the coil, the - side of the coil, and the ungrounded side of the points. You should have 12 volts at each of these places. If not, you have a problem somewhere.

Okay,
I checked it out and this is what I've found:
1. 12v on the coil on both terminals (+) and (-)with the ignition switch on. Crank the engine and the (+) terminal drops to 9V.
2. I unhooked the wire at the points on the distributer that leads to the (-) coil terminal and connected a test light probe. I hooked the other end to the (+) battery post on the starter. When I crank the engine the test light flickers on and off as the points open and close. However, this only happens if the ignition switch is off. Turn the ignition switch on and no flickering test light when the points open and close. Ignition switch Bad?
I'm stumped.
I tested the distributer backing plate for ground, it was fine.
Anyone have any ideas? I don't know where to go from here.

Hook your test light to ground instead of 12v and do your probing with it hooked up that way. If you have it connected to 12v, it will only light when you touch a lower voltage(like ground). If you touch 12v with it it will not light. You have to have a difference in voltage across it to make it light. This is probably why you only see it when your igition switch is off. Are you getting spark anywhere? Pull the high voltage coil wire our of the distributor and hold it close to a good ground(engine block) while you crank the engine with a remote starter switch or have someone run the ignition switch for you. See if you get any spark there. If you have it there, plug that wire back into the distributor and pull a plug wire off at the plug and try the same with it.

Did you replace the points/condensor? If so and you still have the old ones, re-install them and try it. I've been there, the new condensor was bad and it would not start, spent several days out thinking myself. Engines won't run with bad condensors. Aloha

Your other info about the wire from the solenoid
beibg battery voltage is correct. Through the
solenoid action, battery voltage is applied to
the + side of the coil. When cranking is complete
the voltage goes from the battery to the ignition
and then through whatever resistance is used to
the + side of the coil. If you are in doubt of
the ignition switch or wiring to the + side of the coil, run a jumper wire from the + side of the
battery to the + side of the coil. This will
crank the engine if the points are set right. It
will burn the points during prolonged running, but
won't hurt to run for awhile on a test. I can
verify that if you have a bad condenser, you won't
get spark. Also, check your pigtail lead from the
negitive side (-) of the coil after it goes in the
distributor and make sure the insulation is not
broken and touching the inside of the distributor.

Truck Tinker from Talking Rock, Ga.