Wrong Alternator?
At one time, the aftermarket coils were racing oriented. These coils were internally wound make the ignitions work better at high rpm (lets call 4000 - 6000 rpm high). Generally this was a tradeoff on durability and even performance at low to mid rpms.
And/or measure for drops directly.
The trick in looking for drops is to remember that voltage only drops where current is flowing through resistance.
Here's an example of a '69 I just posted for someone else. So lets look at it.
Key off, headlight switch one click out.
Voltage at R6 alternator terminal indicates a 0.1 V drop.
There's no current flowing in the R6 wire. So even if the R6 wire is in terrible condition, we can safely conclude we would measure 12.7 V at the main splice if we could probe it directly.
We can then further conclude that another .1 Volts was lost between the main splice and the B2 terminal on the headlight switch.
Remove the current and the votlage will be same everywhere.
Lets look at another couple examples.
Engine running, looking for voltage drops that would effect voltage regulation
What do we see in the diagram above?
We measure 13.65 V at the battery, and the ammeter indicates charging current of about 5 amps.
Now lets look for drops. We could measure voltage to ground, or we measure votlage differences along the path current is flowing.
The advantage of the latter is that it eliminates measurements that include resistance in ground connections, and with some meters it allows the use of a more sensitive scale.
First lets measure the drop between the alternator and the battery, as well as the voltage to ground.
What's the difference in voltage?
So we know there is a loss of .9 volts between the alternator and the battery. So maybe a tenth is lost in ground connections. Therefore most of the issue is in the posiitve wiring.
Now lets measure voltage and drops at the regulator input.
What do we see here?
For one, I chose to measure at the ballast resistor because it was easier to contact with the probe.
Looks like a very similar drop in voltage.
Analyzing the results points to a problem along the current path shared by the battery and the ignition circuit.
Lets say the parking light test at the top of this post was done with the same car.
That showed us that for roughly 5 amps, a 0.1 Volt drop occured between the battery and the main splice.
Our ammeter indicates about the same current in this case - except going the other way.
Pretty much the only conclusion here is the most resistance is between the alternator output and the main splice.
And the must vulnerable connection in that line is at the bulkhead multi-connector. So that would be where to look first.
Sometimes a plain old stock coil is better than the one marketed as the uber coil of the year.
At one time, the aftermarket coils were racing oriented. These coils were internally wound make the ignitions work better at high rpm (lets call 4000 - 6000 rpm high). Generally this was a tradeoff on durability and even performance at low to mid rpms.
Del mentioned voltage drops. It would be good to check the voltage to ground (13.6 V) at several locations in the system.
And/or measure for drops directly.
The trick in looking for drops is to remember that voltage only drops where current is flowing through resistance.
Here's an example of a '69 I just posted for someone else. So lets look at it.
Key off, headlight switch one click out.
Voltage at R6 alternator terminal indicates a 0.1 V drop.
There's no current flowing in the R6 wire. So even if the R6 wire is in terrible condition, we can safely conclude we would measure 12.7 V at the main splice if we could probe it directly.
We can then further conclude that another .1 Volts was lost between the main splice and the B2 terminal on the headlight switch.
Remove the current and the votlage will be same everywhere.
Lets look at another couple examples.
Engine running, looking for voltage drops that would effect voltage regulation
What do we see in the diagram above?
We measure 13.65 V at the battery, and the ammeter indicates charging current of about 5 amps.
Now lets look for drops. We could measure voltage to ground, or we measure votlage differences along the path current is flowing.
The advantage of the latter is that it eliminates measurements that include resistance in ground connections, and with some meters it allows the use of a more sensitive scale.
First lets measure the drop between the alternator and the battery, as well as the voltage to ground.
What's the difference in voltage?
So we know there is a loss of .9 volts between the alternator and the battery. So maybe a tenth is lost in ground connections. Therefore most of the issue is in the posiitve wiring.
Now lets measure voltage and drops at the regulator input.
What do we see here?
For one, I chose to measure at the ballast resistor because it was easier to contact with the probe.
Looks like a very similar drop in voltage.
Analyzing the results points to a problem along the current path shared by the battery and the ignition circuit.
Lets say the parking light test at the top of this post was done with the same car.
That showed us that for roughly 5 amps, a 0.1 Volt drop occured between the battery and the main splice.
Our ammeter indicates about the same current in this case - except going the other way.
Pretty much the only conclusion here is the most resistance is between the alternator output and the main splice.
And the must vulnerable connection in that line is at the bulkhead multi-connector. So that would be where to look first.
