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Vehicle wiring tap-point record

Which wire did you tap, where, and what did it read with the key off, on ACC, running and cranking? Write it once and the next installer will not have to guess.

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Free: enter your name and email and we send you the files. Excel record and printable Word sheet. No macros.
  • 12 V and 24 V
  • Four states per wire
  • Battery check first
What's inside

Every tapped wire, measured and photographed

For installers who wire trackers, MDVRs, relays and sensors, and for the fleet that wants to know later what was connected where.

  1. 01

    Start

    Vehicle, system voltage and a battery check at rest and running before any tap.

  2. 02

    Reference

    Typical thresholds for 12 and 24 V, rest-voltage bands and what each function should show.

  3. 03

    Tap points

    50 rows: function, color, place, pin, tap method, fuse, four readings, checks and photo.

  4. 04

    Summary

    Pass, Fail and Incomplete counts, rows without a photo, and ready to connect or not.

  5. 05

    Word sheet

    A landscape page to fill at the vehicle with a pen, then copy into Excel.

Four states

One wire, four readings

Measure each wire to the battery negative with the key off, on ACC, with the engine running and while cranking. The pattern tells you what the wire really is.

  1. Key off

    B+ reads live, ACC and IGN read dead, ground reads close to zero. A wire that is live here is not an ignition wire.

    Off

  2. ACC

    ACC turns live. IGN may or may not, depending on the vehicle: the sheet records it without judging.

    ACC

  3. Engine running

    B+, ACC and IGN read live. B+ should sit in the charging range, which shows the alternator is working.

    Run

  4. Cranking

    Record the lowest reading while the starter turns. A deep dip explains a device that restarts on every start.

    Crank
Reference values

The thresholds behind each check

The rest-voltage bands come from Battery University BU-903. The other values are typical starting points: replace them with your vehicle and device documents. For 24 V the workbook uses its own column.

Reference values in the workbook, 12 V system
Value12 V system
Live at or above11.0 Vtypical
Dead at or below1.0 Vtypical
Ground drop at most0.2 Vtypical
Charging range, engine running13.2 – 16.0 Vtypical
Battery at rest, about 100%12.65 V
Battery at rest, about 75%12.45 V
Battery at rest, about 50%12.24 V

Typical value. Replace with your vehicle or device datasheet value.

Tap points preview

The sheet catches the wrong wire

Each function has an expected pattern. A reading on the wrong side of a threshold marks that state No and the row Fail.

tracom-vehicle-wiring-tap-point-record-en.xlsx
FunctionColorPinOffACCRunCrankResult
B+ constantRedF1212.6012.4014.1010.20Pass
IGN (ignition)YellowC3-50.000.3014.009.80Pass
GND (ground)BlackN/A0.020.030.060.15Pass
The three example rows of the file, in volts. A wire meant as ACC that reads live with the key off would show No in the Off check and fail the row: it is a constant feed.

Why record tap points

Most tracker faults that look like device faults start at the tap: an ignition wire that is really a constant feed, a ground on a painted bracket, a supply that drops below the device minimum while cranking. A year later, a new installer opens the dash and has to find every joint again.

One row per wire, with four readings and a photo, answers both problems: it proves the wire was right on the day, and it shows the next person where to look.

How to measure

Put the black probe on the battery negative, not on the nearest metal, and the red probe on the wire. Read it with the key off, on ACC, with the engine running and while cranking. For the ground wire, measure between the ground point and the battery negative: the reading is the drop, and it should be close to zero.

ACC or IGN?

On many vehicles ACC stays live in the accessory position while IGN waits for the run position, and some cut ACC while cranking. The sheet expects ACC to be live on ACC and running, and IGN to be live only when running. If your vehicle behaves differently, change the pattern on the Reference sheet.

The battery check

A weak battery makes every reading look low. Before any tap, read the battery at rest and with the engine running. Battery University gives about 12.65 V for a full 12 V battery at rest, 12.45 V for about 75 percent and 12.24 V for about 50 percent, measured after a rest period at 26 °C.

Limits and sources

Rest-voltage bands: Battery University BU-903, re-read 2026-11-03 (readings at 26 °C after a 24-hour rest). The live, dead, ground and charging values are typical starting points used in tracker installation documents, not standards and not Tracom specifications. The record shows readings on one day. It does not approve an installation.

Related Tracom solution

Wire a Tracom device on readings, not guesses

Installing Tracom ST100 or M1N? Fill the tap points first, then take the device supply range and input levels from its datasheet and set them in the configuration file.

  • Advanced configuration files. Set ignition detection to match the wire you recorded.
  • Secure access and immobilization. Record the relay tap the same way.
  • Tamper-proof security. If your configuration reports power-cut events, compare them with the tap you wrote down.
Questions

Tap-point questions

Wiring a new vehicle type? Talk to Tracom.

Why measure to the battery negative?

Because a nearby metal part may not be a good ground. Measuring to the battery negative shows the real voltage on the wire and the real drop on the ground.

What is the difference between ACC and IGN?

ACC is usually live in the accessory key position, IGN in the run position. Vehicles differ, so the record keeps both readings and you can change the expected pattern.

Why record the cranking voltage?

A deep dip while the starter turns can make a device restart. Compare it with the minimum supply in your device datasheet.

Are the thresholds Tracom specifications?

No. They are typical starting values. Take the device input levels and supply range from your device datasheet.

Does it work for 24 V trucks?

Yes. Choose 24 V on the Start sheet and the workbook uses the 24 V column. Check those values against your vehicle too.

What is Tracom's role here?

Tracom makes the devices. The record is a general template for any installer. It does not approve an installation.

Next step

Measure before you connect

Send us the vehicle make and model. We will tell you which wires installers usually record for it.

Contact Us Get the record
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