Should the 12V Lamp Always be Lit Even when the Car is not Running and the Keys are Out

Updated 09/17/2012 | Published 09/13/2012

Products Featured in This Question

Starter Solenoid - SPST - 12 Volt - 100 Amp - Continuous Duty - Grounded

(13)

$35.13

Firestone Fuse Circuit Tap Kit

(40)

$22.03

Hook Probe Circuit Tester

(65)

$13.35

Question:

Should the 12V lamp always be lit even when the car is not running and the keys are out? I have the black wire connected to the battery with a 40amp inline breaker. Thank You

asked by: Josh D

Expert Reply:

The 12-volt power wire from your 7-way connector will always be hot if it was attached to the positive terminal of the vehicle's battery, even with a 40-amp circuit breaker installed. To prevent your trailer from constantly drawing power from your vehicle's battery, I recommend installing the Battery Isolation Solenoid, # PK5231201, inline on the power wire. This will prevent your vehicle battery from draining when a trailer is connected. I have attached a photo that shows how the wiring would be installed.

If you are looking at the unit with the dome facing up as it is shown on the product page, the left terminal is the input from the vehicle battery, the right side is the output to the 7-way connector and the middle should be connected to a switched ignition source, such as a powered antenna motor wire or radio wire. I would recommend using a circuit tester like part # PTW2993 to test for wires that only have power when the ignition is on.

You could also use a fuse tap like part # F2526 if a fuse is easier to locate than a wire.

expert reply by: John H