Power ports
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Cargo Master
Joined: Jun 2008
Posts: 2,923
Likes: 33
From: Sacramento Area
The coil would be engaged when the switch is on, but not when the ign power is on. If you used a center off dual pole dual throw switch, you could wire a 2nd relay to turn off the ign power. I use relays all the time, they are built for it and the coil doesn't draw much for amperage, so I wouldn't worry about having a relay on whenever the circuit is engaged. It is still better then diodes. Not only do they get hot, but there is a voltage loss across them, so there is still wasted power.
Junior User
Joined: Feb 2009
Posts: 73
Likes: 1
I wire the circuit I showed you all the time for an "override" switch for cd players in cars. With the switch off the wire works as normal, when you turn it on it disconnects from ign wire and connects to constant on wire. When you switch it off, it disconnects from constant and goes back to ign. The wire disconnects first, so no chance of back-tracing. With a "make-before-break" switch, you could have that happen, but even then, in most cases of a 12V system, it would not be a big deal.
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Cargo Master
Joined: Jun 2008
Posts: 2,923
Likes: 33
From: Sacramento Area
I wire the circuit I showed you all the time for an "override" switch for cd players in cars. With the switch off the wire works as normal, when you turn it on it disconnects from ign wire and connects to constant on wire. When you switch it off, it disconnects from constant and goes back to ign. The wire disconnects first, so no chance of back-tracing. With a "make-before-break" switch, you could have that happen, but even then, in most cases of a 12V system, it would not be a big deal.
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Turbo Dog
1967 - 1972 F-100 & Larger F-Series Trucks
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