- Joined
- Jun 2, 2012
- Messages
- 25,363
- Reaction score
- 8,371
- Points
- 113
- Location
- canada
- Vehicle Year
- 1994
- Make / Model
- Ford
- Transmission
- Manual
The resistor was to lower running voltage at the coil (and points) so they didn't run as hot
Most car makers had separate START and RUN wires to the Coil
12volt coil is fine at 12v, problem is when alternator is on its running at 13.5-14.5volts so coil runs way hotter than it needs to
The resistor lowers running voltage by 4 volts, so coil runs at 9-10volts which generates about 20,000volts to spark plugs
But when starting battery voltage DROPS to 9-10volts because of starter motors high AMP draw
If you passed that thru the resistor its 5-6volts, so very very weak spark
As said there was an "I" post on the 4 post starter relays, it has the 9-10volts to send to coil when starter is active, then 0v when starter is off, so just the one extra wire to the Coil + terminal
Once electronic ignitions were here to stay, and coils got better, there was no need for the resistor
So START and RUN both power spark system directly
Most car makers had separate START and RUN wires to the Coil
12volt coil is fine at 12v, problem is when alternator is on its running at 13.5-14.5volts so coil runs way hotter than it needs to
The resistor lowers running voltage by 4 volts, so coil runs at 9-10volts which generates about 20,000volts to spark plugs
But when starting battery voltage DROPS to 9-10volts because of starter motors high AMP draw
If you passed that thru the resistor its 5-6volts, so very very weak spark
As said there was an "I" post on the 4 post starter relays, it has the 9-10volts to send to coil when starter is active, then 0v when starter is off, so just the one extra wire to the Coil + terminal
Once electronic ignitions were here to stay, and coils got better, there was no need for the resistor
So START and RUN both power spark system directly