[whatwouldscoobydo]

Put a complete wiring harness from a 75 nova in my 38 stude.The nova had a six cylinder with eletronic ignition.I have about a 74 350 with points distributor.Used the same wire going to the coil.After a few hundred miles,burnt up the wire in the distributer to the points.Replaced the wire and points,and installed a resister (from the auto parts store)in line before the coil.Had 12 volts in and about 7 volts out to the coil.Now after driving it a few times decided to check things and I have 12 volts running thru and to the coil! Any Ideas?Tom

[goldenrog]

If the points are open when you test the voltage, you will have available voltage every where in the circuit. When the points are closed and the circuit is operational, you should find the 7 or so volts you're looking for.

[docvette]

Doc here,

As goldernrog said..you have to test the coil under a load..(points closed) to see the 7 volts..If the load is removed, current goes low, voltage goes high..

It is the same as putting a meter on the ground side of a light bulb, with the ground removed..you will read 12 volts at the ground through the bulb, but the light isn't lit..(no current draw) when you ground the wire to the light, the bulb lights..and is drawing max (High)current voltage goes to zero...

Recheck it with the points closed..bet you'll find it's 6 to 9 volts...

Doc

[whatwouldscoobydo]

Ok, noticed small voltage .9 volts (with key off) on the line going to the resister.It bleeds off to 0 volts with the volt meter connected.Replaced resister with 1.81 ohm resister,this was the highest resistance they have.With truck running, I have 14.01 volts going to resister, out the other side theres 10.97 volts.Should I take the meter reading from the line between the coil and ditributer?

[goldenrog]

Ok, the small amount of voltage may be coming from the capacitor (condensor). Is the resistor you're using automotive? If it is, the voltage you have should be fine. If not automotive, hit up your parts store for a ballast resistor for an early (60's-mid 70's) Chrysler product.

[whatwouldscoobydo]

Yes the resistor is auto ,and I believe it is a mopar.Haven't tried this time to see what the voltage is with the motor not running but the key on.If the points are closed is this when I should see 6-7 volts?Thanks for all the help.Tom

[docvette]

Doc here,

You want to test your system this way, Set the points to "Closed", With that done, Measure the Voltage on the line coming from the Ignition primary and ignition secondary (the solenoid) or the upstream side of the ballast resistor.

It should read, 12 volts continueous...Static with the key on, or cranking..(if you crank it return it to the points closed position for further testing)

Then Check the downstream side of the coil power wire (Ballast to Coil wire) With the points closed the voltage should read between 6 to 9 volts ...

When (with the points closed) you turn the key off, it should drop to zero right off..The Closed points should pose a direct load to ground on the Capacitor/RFI filter and discharge it right away.

If you have that, you should be fine, as far as ballast, primary and secondary ignition...

If you are worried about possible harness burnout again in the future, just add an in-line fuse holder and fuse.

To figure out the proper draw of the coil, measure with an ohm meter the primary side of the coil and case ground..

The amount of resistance divided by the voltage will give you the draw..Then add a "Little" bit more on the fuse rating and make it a Slo~blow fuse...

Say if the draw is 4 amps..make it a 5 slow blow..and the reason for this is, the coil is subject to current "Spikes" as the points open and close..

The slow blow will Buffer this effect a bit..instead of poping at random (like when you don't need to lose ignition coil power..merging onto a freeway..)you can safely raise the value up to about 7 1/2 or 10 amps if you suffer random fuse blowout..but after that, it won't much protect the wires between source current and the load..and defeat the purpose of the fuse..

Doc

[whatwouldscoobydo]

Checked it with the points closed,6-7 volts,but didn't check it while cranking the motor.So is the voltage of 10+ volts while the engine is running ok?

[docvette]

Originally Posted by whatwouldscoobydo

Checked it with the points closed,6-7 volts,but didn't check it while cranking the motor.So is the voltage of 10+ volts while the engine is running ok?

Doc here,

Yup. The voltages rise with the aid of the alternator.

The Crank test only shows the Secondary is hooked up, and that the wire is on the right side of the resistor..since it is only momentary, (while cranking) It's not a big problem if it's on the wrong side..The primary is what counts.

Doc