Centerline
Well-Known Member
I don't mean to insult anyone's intelligence here but the thought occurred to me that some may not understand what a relay is and why it's a good idea to run relays for headlights on our older cars.
If you've ever seen a 50's or early 60's car at night you may have noticed their headlights seem to dim a little when the engine is idling, for instance at a red light. But when the light turns green they brighten up again when once the engine rpm is increases. Running relays solves this problem.
Now I'm not an electrical engineer, but here is my understanding of what a relay is. Just think of a relay as a high voltage switch. That's all it really is. It's an electrically operated switch that uses a low voltage input to turn itself on and off while at the same time it provides a higher voltage or high current circuit with power. It's basically a safety feature. It allows you to use higher voltage to power the lights without passing that power through 60+ year old switches that may or may not be capable of handling a high voltage input.
In the case of our older cars we use relays to provide power directly from a high amp source such as the starter power circuit or alternator output and run that power directly (through the relay) to the headlights. This gives us brighter headlights that won't dim when the engine is at idle. The light switch is simply used to switch the relay on and off for the low beams and the bright light switch on the floor (which receives its voltage from the light switch) is used to switch the relay on and off for the high beams. At least that's the way I use them.
Using a relay allows you to run higher amperage wire as well. The headlights on our old Mopars usually use a 15 amp circuit and 16 gauge wire. The power for this circuit comes through the dreaded bulkhead connector through the headlight switch then through the dimmer switch, back through the dreaded bulkhead connector and eventually to the headlights. Each connector in the circuit robs it of a little voltage and by the time the power gets to the bulbs it is somewhat less than what it started out to be. This is especially true with 60 year old connections and wires.
When you use a relay in the circuit you can take that lower power provided by the stock headlight circuit and use it to switch on a relay which gets its power directly from a high amp source through a higher rated wire and higher amp breaker. The result is more reliable and brighter lights. It's pretty much that simple.
On my '64 Polara I run dual relays that draw their power directly from an insulated terminal block on the firewall. This terminal block gets its power from the positive connector on the starter and also provides power to the fuse panel thus eliminating the dreaded bulkhead connector. The two wires heading off at 3 o'clock from the terminal block go to the two relays.
From this terminal block I run 10 gauge wires (overkill) through twin remote 30 amp circuit breakers (also overkill) to the relays and from there on to the lights. I could have used 12 gauge wires and 20 amp breakers and it would work just as well. (The circuit breakers are those double barreled looking things just below the yellow wires and gray clamp in this pic below.) They're switched using power from the stock headlight switch and dimmer switch. I've used this system on several cars and it works flawlessly.
If you've ever seen a 50's or early 60's car at night you may have noticed their headlights seem to dim a little when the engine is idling, for instance at a red light. But when the light turns green they brighten up again when once the engine rpm is increases. Running relays solves this problem.
Now I'm not an electrical engineer, but here is my understanding of what a relay is. Just think of a relay as a high voltage switch. That's all it really is. It's an electrically operated switch that uses a low voltage input to turn itself on and off while at the same time it provides a higher voltage or high current circuit with power. It's basically a safety feature. It allows you to use higher voltage to power the lights without passing that power through 60+ year old switches that may or may not be capable of handling a high voltage input.
In the case of our older cars we use relays to provide power directly from a high amp source such as the starter power circuit or alternator output and run that power directly (through the relay) to the headlights. This gives us brighter headlights that won't dim when the engine is at idle. The light switch is simply used to switch the relay on and off for the low beams and the bright light switch on the floor (which receives its voltage from the light switch) is used to switch the relay on and off for the high beams. At least that's the way I use them.
Using a relay allows you to run higher amperage wire as well. The headlights on our old Mopars usually use a 15 amp circuit and 16 gauge wire. The power for this circuit comes through the dreaded bulkhead connector through the headlight switch then through the dimmer switch, back through the dreaded bulkhead connector and eventually to the headlights. Each connector in the circuit robs it of a little voltage and by the time the power gets to the bulbs it is somewhat less than what it started out to be. This is especially true with 60 year old connections and wires.
When you use a relay in the circuit you can take that lower power provided by the stock headlight circuit and use it to switch on a relay which gets its power directly from a high amp source through a higher rated wire and higher amp breaker. The result is more reliable and brighter lights. It's pretty much that simple.
On my '64 Polara I run dual relays that draw their power directly from an insulated terminal block on the firewall. This terminal block gets its power from the positive connector on the starter and also provides power to the fuse panel thus eliminating the dreaded bulkhead connector. The two wires heading off at 3 o'clock from the terminal block go to the two relays.
From this terminal block I run 10 gauge wires (overkill) through twin remote 30 amp circuit breakers (also overkill) to the relays and from there on to the lights. I could have used 12 gauge wires and 20 amp breakers and it would work just as well. (The circuit breakers are those double barreled looking things just below the yellow wires and gray clamp in this pic below.) They're switched using power from the stock headlight switch and dimmer switch. I've used this system on several cars and it works flawlessly.
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