LS1 Ignition On & Start Relays

[dave w]

"Back in the day" the ballast resistor was not in circuit during starting, but only was switched into the circuit during running conditions to prevent coil overheating. During starting, the resistor was switched out and the full 12 volts was applied to the coil-not the 8 to 9 volts that the ballast resistor provided.

I'm thinking the starter "R" terminal is the source for the coil when the ballast resistor is bypassed? Usually the voltage available with the starter spinning the engine is less than 12 volts. I'm thinking the available voltage is maybe in the range of 10.5 volts when the starter is spinning the engine, The stater motor is a HUGE draw on the available battery voltage.

dave w

[lionelhutz]

Yes, the R terminal did the bypass.

Is it a GM? A 68 GM would have an ignition switch that provides ignition power even in the start position.

[dave w]

Yes, the R terminal did the bypass.

Is it a GM? A 68 GM would have an ignition switch that provides ignition power even in the start position.

It's a 1968 GM Oldsmobile. I could not find an ignition switch wire that had power in both run and start. I found wires powered with either run or start. Considering the vehicle is half a century old, with multiple owners, it seem likely the wiring is not 100% original.

dave w

[lionelhutz]

Is the key in the column? They sometimes did that when the switch was out of adjustment. It can just be moved up or down the column to adjust.

[sturgillbd]

Instead of relays, you could simply use two diodes. Diodes will have to handle whatever the average current is on the device it is feeding but will work fine.

Brian

[dave w]

Excellent idea, these should work https://www.mouser.com/datasheet/2/4...ries-63289.pdf

I'm likely going to use relays, available at Auto Parts Stores. It's an automotive application.

dave w

[lionelhutz]

Use smaller diodes like a 1N4007 to power one relay.