Identifying Where To Splice D+/Signal Wire Guide
A multi-meter will be needed to measure the 12V sources to confirm which wire should be spliced into for the D+ 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.
Ignition Circuit—Cranking Source
A multi-meter will be needed to measure the 12V sources to confirm which wire should be spliced into for the D+ wire. Set it to DC Volts that can read up to 20V or 200V. It is recommended to review your vehicles instructions or schematics as there will be varying models. The following is an example:
The first step is identifying your 12V power sources within the ignition wires. You will find the following:
Constant 12V source—the Key is in Lock or not connected. Typical for running alarm systems, clocks, etc.
Accessory Source (12V supply when the Key is in ACC)
Ignition Source (12V supply when key in ON)
Cranking source (12V supply when starting/running)
1. To find a constant 12V source, you will use the positive probe (typically red) of your multi-meter. Start by grounding the multi-meter to a vehicle ground point that needs to be metal, such as a door hinge. Ensure that the ignition switch is in the Lock or Off position. Once you are sure that the ignition is off, proceed to probe the wires on the probe area of the ignition switch while observing the multimeter readings. When you probe a wire that supplies 12V (12.3~12.5V or close) you know you have found a constant 12v supply.
2. The accessory source supplies 12V when the key is in ACC. It can also supply 12V when the key is in the second position (ON). With the key on ACC, you will use the positive probe of your multi-meter in the probe area, except for the constant 12V found in step 1. When the multi-meter reads around 12V you have found the accessory source. To confirm, measure again with the key in OFF from ACC and observe the voltage drop to 0. When you put the key back in ACC, it should go back your 12V value. If this was not the case, you may have found the ignition source or cranking source.
3. The ignition source is common when dealing with electronic devices which require more current. When a car is running (engine on) the ignition (on) source is supplying 12V. You can however use ignition switched power when the car is not running but the key is in the ignition (on) position. With the ignition off, you will use the positive probe of your multi-meter in the probe area, except for the constant 12V found in step 1. The voltage should be 0. Next, turn the key to ignition (on). If you selected a proper source, you should now be reading a 12V value. Double check by turning the key back to ACC, observing if the voltage drops to 0, then when turning the key back to ignition (ON), the value should go back up to 12v. If this was not the case, you may have found the cranking source.
4. The cranking source provides 12V only when the engine starter is engaged. It is generally used for remote starters and alarm system in which case the ignition is bypassed, and electronic device is acting as the ignition switch for the cranking position. With the ignition off, you will use the positive probe of your multi-meter in the probe area, except for the constant 12V found in step 1. Next step will be to turn the key to the cranking (start) position. If you have selected the proper source, you will now read a positive voltage source (around 12v) only while turning the key to the cranking (start) position. Confirm by releasing the key, then turning the key back to the cranking (start) position. If the voltage drops to zero when the key is released, then back to 12v when the key is in the cranking (start) position, you have found the cranking source. With the source found, you may splice a D+ on this source.
Alternator
It is recommended to review your vehicles instructions or schematics as there will be varying models. The vehicle needs to be off. Most alternators will have three wires connected (BATT +, BATT -, Ignition circuit).
The purpose is to find the ignition circuit by eliminating the 12V constant source. To find a constant 12V source, you will use the positive probe of your multi-meter. Start by grounding the multi-meter to a vehicle ground point either the battery negative post or an area on the chassis that needs to be metal. You will then need to 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 and we can now eliminate it.
Turn on the ignition and test the other two wires for a 12V+ signal besides the one you identified previously. Once that one is identified that wire will be the hot in run/start ignition circuit. With the ignition circuit identified, you can turn off the vehicle and the D+ signal wire can be spliced into that wire.
Engine Bay Fuse Block
It is recommended to review your vehicles instructions or schematics as there will be varying models. By reviewing the fuse layout diagram on the vehicle, the accessory/auxiliary fuse should be identifiable. You can also test using a multi-meter on the fuse block. Start by grounding the multi-meter to a vehicle ground point either the battery negative post or an area on the chassis that needs to be metal. The first step is identifying your 12V power sources within the ignition wires. You will find the following:
Constant 12V source—the Key is in Lock or not connected. Typical for running alarm systems, clocks, etc.
Accessory Source (12V supply when the Key is in ACC)
Ignition Source (12V supply when key in ON)
The fuses should have a metal contact on top of them where you can probe the positive meter line and get a reading. With ignition off, tap the metal fuse contact points until you find a live 12V point by checking the 10Amps fuse first. This will be your constant 12V source.
With ignition ON, tap the positive meter probe on the metal fuse contacts and identify another 12V source by. Once identified, confirm by turning the ignition OFF and re-measure the same fuse. If the multi-meter shows 0V, this is your ignition source. You can splice into the fuse box by using a fuse tap with your own 10A fuse.
When the D+ signal is spliced into one of these circuits and the rest of the installation is complete on the device, the unit should turn on and off with the vehicle.
This is a brief introduction on how to wire the D+ signal wire to a vehicle and we always recommend this is done by an experienced installer or professional. If you have any other questions or concerns, feel free to call or email our customer support team here.
Sprinter Van
Connecting the D+ can be possible in a sprinter van with the driver panel underneath the seat which has connections from your engine (starter) to your auxiliary battery.
