Tesla Model S Front HVJB

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Tesla gen 2 front HVJB (shown with HV cable)


The second-generation front HVJB (Tesla p/n: 1028843-01-A & 1028843-01-C) found in the early (late2013-2016) Model S, isn't particularly useful on its own, but it does enable a number of other HV accessories as literally plug and play.

This GEN2 Front HVJB replaced the earlier (2012-Jan2014) DC-DC Converter that had served as the Front HVJB on the original production Model S, and which had troublesome internal fuses that were difficult to replace.

Unless otherwise noted, info below was sourced from: https://www.diyelectriccar.com/threads/hacking-the-tesla-model-s-front-junction-box.193729/


Case measurements:

  • L : 9 1/4in case (10 3/4 to allow for LV connector and ground connection)
  • W: 8 1/4in case (9 1/4 to allow for HV plugs to A/C, DC-DC,etc. and HV in)
  • H: 2 3/4in case (3 1/4 if the mounting bracket still fitted)

HV hole size:

  • less than 15mm, hard to get actual without disassembly, probably 13-14mm diameter



There are 4 colour-coded HV sockets found along the top side of the unit (as oriented with the front label right side up) that correspond to particular HV systems. From left to right, they are:

  • Grey: Battery Fluid Heater - fused internally at "F1" (20A)
  • Blue: DC-DC Converter - fused internally at "F4" (20A)
  • Orange: A/C Compressor - fused internally at "F2" (40A)
  • Brown: PTC Cabin Heater - fused internally at "F3" (40A)

These HV connectors are KET HVSC 280 series, and, while mating plugs for these sockets are known, they are not easily available. For reference, the mating plugs are:

  • Gray (fluid heater): MG655774 (key B)
  • Blue (DC-DC): MG655776 (key D)
  • Orange (A/C): MG655773 (key A)
  • Brown (PTC heater): MG655775 (key C)


The LV connector on the bottom left side is a 12-pin Molex MX150 series (Molex p/n: 33472-1201). Only 6 of the 12 pins are populated, as follows:

LV pinoutConnector-Tesla-FJB.png(harness view)
pin function
4 12V
5 PWM in
6 STATUS out
10 GND
11 HVIL in (not needed)
12 HVIL out (not needed)

The purpose of this LV connector is to control the built-in PWM circuit for the battery heater that is attached via the grey HV plug. The PWM control parameters are known and are detailed in the Tesla Model S Battery Heater article. As noted, HVIL pins 11 & 12 seem to have no effect on the function of the HVJB and can be left de-pinned.