Source of 12V inside engine

R

rglosem

Junior Member
1953 Crestline converted to 12V system. What would be a good point inside the engine bay to get a 12V source that is hot whenever the engine is running? Would rather not have to run wiring from inside the car if possible.
 
the bat terminal is direct to battery. in a generator system.
The armature terminal only has power when engine is running but the voltage varies until cutout relay is energized then it is connected to system voltage.
Since it is not “stock” it’s hard to know what wires are there.
 
taken literally the OP's request appears to me an odd one. in that the request is for power only when the "...engine is running...". i'm not sure that that's what was meant.

anyway...

IIRC, standard 40's and 50's "bat" terminals on voltage regulators are generally considered an "unswitched" connection. meaning they are "hot" at all times and essentially an extension of the "hot" terminal on the battery. in which case one could just as well connect a wire to the "bat" terminal on the voltage regulator or to the "hot" terminal on the battery, as they would be, from a circuitry POV, equivalent.

and i may be wrong, but i've taken the meaning from the OP's initial post as wanting a "switched" connection. meaning a connection that would provide power only when the ignition key had been turned to the "on" position. and if what've i've written above is correct (and it may not be) then the "bat" terminal on the voltage regulator would not be what the OP is looking for.

maybe a bit of clarification is in order? :)
 
Bat terminal on regulator as 12 volt source to 30 on a 5 pin relay.
Car side of ignition ballast resistor to 86.
Ground 85.
87 will have 12 volts when engine is running.
 
If it needs to be switched, I'd recommend using one that's amp rated for the needed function and wired where you can reach it. Use an in line fuse if coming from the start solenoid.

The ignition switches are generally already used up as far as connecting any other accessories. Overdrive would be the only one I'd try to use if you want ignition on/off. The charging circuit is not a fused circuit on the old cars and neither is the horn or the engine starting circuit. The ignition needs a clean power source with no RF interference to complicate things. It comes from it's own post on the ignition switch in most cases and they had a good reason for that. The overdrive cars have an interrupter circuit for the coil but it kicks out as soon as the system switches out of overdrive so it's a quick acting circuit but it's still isolated from all the other circuits due to the way the kick down switch and the operating solenoid are wired.

If a fuse is used in a new circuit just be aware that it's there to protect the wire in the circuit. The wire size is what regulates the fuse size. This is about the only advice I can give without knowing what the new circuit is for.
 
I used to wire up fog lights at the phone company garage. We used 50 amp circuit breakers that were turned on by a switch that got its power from the ignition switch. That tuned on the circuit breaker which got its power from the battery side of the starter solenoid. It could be turned off by the fog light switch but if you forgot to turn them off the breaker would automatically turn them off when ignition switch was turned off. You could hook up to 50 amps worth of accessory to the circuit breaker, but the circuit breaker was only tuned on with a small amount of current from the ignition switch. That's the hot ticket rather than hooking into the coil and putting a strain on that circuit.

I meant a relay not a circuit breaker. I've had a stroke and things are a little hard to pull up out of my head. We used Standard LR-32 light relays at work. I never saw one fail in 30-years at work.
 

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Flathead Fever said:
I used to wire up fog lights at the phone company garage. We used 50 amp circuit breakers that were turned on by a switch that got its power from the ignition switch. That tuned on the circuit breaker which got its power from the battery side of the starter solenoid. It could be turned off by the fog light switch but if you forgot to turn them off the breaker would automatically turn them off when ignition switch was turned off. You could hook up to 50 amps worth of accessory to the circuit breaker, but the circuit breaker was only tuned on with a small amount of current from the ignition switch. That's the hot ticket rather than hooking into the coil and putting a strain on that circuit.
Click to expand...

That's essentially similar to hooking up headlight circuits to relays up by the radiator, which then employs a clean power source for bright headlights.
 
Flathead Fever said:
I used to wire up fog lights at the phone company garage. We used 50 amp circuit breakers that were turned on by a switch that got its power from the ignition switch. That tuned on the circuit breaker which got its power from the battery side of the starter solenoid. It could be turned off by the fog light switch but if you forgot to turn them off the breaker would automatically turn them off when ignition switch was turned off. You could hook up to 50 amps worth of accessory to the circuit breaker, but the circuit breaker was only tuned on with a small amount of current from the ignition switch. That's the hot ticket rather than hooking into the coil and putting a strain on that circuit.

I meant a relay not a circuit breaker. I've had a stroke and things are a little hard to pull up out of my head. We used Standard LR-32 light relays at work. I never saw one fail in 30-years at work.
Click to expand...
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587681
 
Flathead Fever said:
I used to wire up fog lights at the phone company garage. We used 50 amp circuit breakers that were turned on by a switch that got its power from the ignition switch. That tuned on the circuit breaker which got its power from the battery side of the starter solenoid. It could be turned off by the fog light switch but if you forgot to turn them off the breaker would automatically turn them off when ignition switch was turned off. You could hook up to 50 amps worth of accessory to the circuit breaker, but the circuit breaker was only tuned on with a small amount of current from the ignition switch. That's the hot ticket rather than hooking into the coil and putting a strain on that circuit.

I meant a relay not a circuit breaker. I've had a stroke and things are a little hard to pull up out of my head. We used Standard LR-32 light relays at work. I never saw one fail in 30-years at work.
Click to expand...

Flathead, I’ve had brain farts lots worse than that! I for one have appreciated your intelligent input to the Barn for a long time, and hope to keep up as good as you have. Keep on trucking!
 
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