How To wire D+ signal
When hooking up our DC-DC isolators and chargers, there are multiple ways to connect the D+
signal wire. The D+ signal wire is used as an on and off switch for these devices, its main
purpose is to send a 12V+ signal to the device when the vehicle is running. This is necessary for
devices without a voltage-sensitive relay (VSR) so the unit knows to turn on when the alternator
is running and off when it is not, so it does not drain the starter battery. There are multiple
circuits in a vehicle that are only powered on when the vehicle is running, we recommend
splicing into one of these for the D+ signal.
The first step is identifying which circuit is active when the vehicle is running, which can be
accomplished by reviewing the vehicle's electrical diagram or testing for DC voltage with a
multimeter. Our first recommendation is to check on the alternator itself, most alternators will
have three wires connected ( BATT +, BATT -, Ignition circuit), identify the constant 12V+ which
will be live all the time. To test for voltage set the multimeter to DC voltage on the dial, once that
is set find a common negative on the vehicle either the battery negative post or an area on the
chassis and place the negative lead from the meter there, then splice into one wire at a time to
expose the bare wire and with the positive lead from the meter test on that area. Once the 12V+
constant is identified take note of that wire, then turn on the ignition and test the other two wires
for a 12V+ signal, once that one is identified, that wire will be the hot in run/start ignition circuit.
WIth the ignition circuit identified the D+ signal wire can be spliced into that wire.
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