Electrical 12v switched source uder hood '65

lgbyblock · Jan 22, 2021

I need 12 source (for electric choke) that in hot when the ignition switch is on. My car has manual every thing. Lights, heater blower and horn are only hot when individually turned on. Holly says not to use the distributor battery terminal but it seem like the only source other than straight from the battery. Any suggestions?

wicked93gs · Jan 22, 2021

The starter solenoid "I" terminal should be switched 12v(if I remember correctly)...however, I suggest installing a relay that draws signal from the accesory terminal on the ignition switch(yes, another wire through the firewall somehow) and that powers a distribution block...especially if you plan on adding other such things in the future.

dennis112 · Jan 23, 2021

I am sure it depends on the year of the car BUT I found on a 66 that the heater fan motor has suitable key switched power. The wire would either need to be spiced into or a simple "Y" connector made with the original type Ford Bullet connectors be used. The Y allows you to unplug the appropriate lead in the engine compartment to install it. The added leg lets you tap into the power circuit without cutting the wire.

dmck · Jan 27, 2021

DO NOT USE the ignition coil terminal. The voltage is usually around 5-6 volts once the engine is running. This is deliberate and the coil is designed to work in this way.

Early Mustangs are very poor electrically compared to modern cars.

Do as Wicked93 suggests. A thin wire from the ignition switch to operate a relay. The relay switches a heavier wire from the battery +ve (or the hot terminal on the solenoid) to a fuse block. Take your choke wire from the fuse block.

Use a 'heavy duty' relay capable of switching 40 amps or more ( I did 100A on my '69) coz you never know what else you may want to power from the fuse block.

I ended up rewiring my headlights, horns, spotlights all via smaller relays, from the fuse block. Less voltage drop , less chance of burning out under-dash wiring.

wicked93gs · Jan 28, 2021

dmck said:
DO NOT USE the ignition coil terminal. The voltage is usually around 5-6 volts once the engine is running. This is deliberate and the coil is designed to work in this way.

Early Mustangs are very poor electrically compared to modern cars.

Do as Wicked93 suggests. A thin wire from the ignition switch to operate a relay. The relay switches a heavier wire from the battery +ve (or the hot terminal on the solenoid) to a fuse block. Take your choke wire from the fuse block.

Use a 'heavy duty' relay capable of switching 40 amps or more ( I did 100A on my '69) coz you never know what else you may want to power from the fuse block.

I ended up rewiring my headlights, horns, spotlights all via smaller relays, from the fuse block. Less voltage drop , less chance of burning out under-dash wiring.

You are right, the I-terminal leads to the coil and the resistor wire drops voltage to 9v or so(theoretically) its the S-terminal that you would want:

I still don't reccomend running anything without properly fusing and relaying it though...the only reason Ford didnt do it in the 60s is because relays didn't really exist then...aside from primitive things like the starter solenoid.

Electrical 12v switched source uder hood '65

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