Measuring Front Mount Ignition

Terminal Block: X = Term, ^^^^^^ = Ballast, letter = Ident.

----- ----- ----- ----- ----- ----- ----- ----- - (A) X ^^^^^^^^^ X (B)

..... ..... .X (C)

----- ----- ----- ----- ----- ----- ----- ----- -

1. Black Meter Probe connected to Term C , Red Meter Probe connected to Frame (ground)

Results = ~ 6.5 Volts (battery)

2. Black Meter Probe Connected to Term C, Red Meter Probe connected to Term A

Results = If A has a wire connected to Ignition Switch, Voltage should be < 0.5V If A has a wire connected to Top of Coil, Voltage Should be > 3.5 Volts

3. Black Meter Probe Connected to Term C, Red Meter Probe connected to Term B Results = If B has a wire connected to Ignition Switch, Voltage should be < 0.5V If B has a wire connected to Top of Coil, Voltage Should be > 3.5 Volts

4. Black Meter Probe Connected to Term A, Red Meter Probe connected to B

Results = (Ballast Voltage Drop) ~ (about) 3 Volts is normal.

Results with Points Open = 0 (zero) Volts

If these Voltages are Correct the Voltage at the Top of The Coil will be ~ 2.8 Volts and you will have the "normal" ~ 3 amps @ saturation

Hope This Helps

JMHO

Yes that is correct, but my point is that measuring the Ballast VD will find your problem very easy. You may not have a Physical Block but you must have the SAME test points.

The ignition circuit can be best discribed as operating like a balanced beam.... The Coil and its resistance are on One side.... The Ballast is on the Other. When additional Resistance is found in the Circuit (bad connector/bad Ignition switch) this resistance falls on the Ballast Side of the Beam and the Ballast adjusts (reduces)its resistance to compensate, such that the beam stays balanced. A small change in circuit current results in a large change in Ballast Resistance.

If you measure the Coil Voltage it will remain reasonably constant over the variable range of Ballast and that is normal.

The Voltage Drop Across the Ballast tells you
the "condition" of the circuit.

Hope that explains,

The coil can only change its VD if Current Changes, resistance is constant at Saturation.

The ballast has "Two" dynamic variables... the Current change and the resulting thermal change of resistance. If the current in the circuit goes down... the Ballast Resistance also goes down. Simple Math should tell you that the VD
across that Ballast is MORE Sensitive.

You can lead a horse to water but.....

ALL voltages in my Posts are Static measurements using a Multimeter, with the Points Closed. Your theory is not inacurate but requires a Scope...

I have NEVER EVER said that the the Voltage at the TOP of the COIL.. to Ground is 3.5V... If you look at the Circuit it is 3.5V from the top of the COIL ...to the Metered Battery (C)

When you are Trouble shooting a faulty circuit
95% of the problems will be reduced current because of increased resistance caused by BAD Wire Crimps & Switches... (These devises do not increase current when they Fail)

6.5V @ top of Coil:
Kirchhoffs Law: "The Sum of the Voltage Drops around a DC series Circuit equals the Source or Applied Voltage"

IF you understand that LAW.. Explain your measurement of 6.5 V at the Top of the Coil, When the Point are OPEN. (Appied Voltage = Zero... Sum of VD = Zero) Perhaps you don't Know how to Measure Voltage Drops.

JMHO

1. With the points closed the coil will reach a Max current of ~ 2.8A @ 6.5v applied. This means that the top of the Coil (to ground) will measure less than (<) 3.0 Volts and more than (>) 2.4V.

2. With the Points Open Current flow through the "Coil" is "ZERO".

The meter, measuring itself, is an attempt to prove that the Coil is OPEN (has Zero Current) but the Coil is in parallel with your meter and a short in the dist of >50 Ohms will result in Coil current flow and a delta of ~1.4 Volts, from Battery. That is very hard to see when using an analog meter with current flowing in the coil.

Barbwire works, but what proves that NO current is flowing in the Coil? ... A Series Component VD!

Regards,