Digital Tachometer for Harley Davidson Sportster (Part 13 - Wiring harness and installation)

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Once we have the PCB, the housing and the bracket, now we “only” need the harness. There are a thousand ways to connect the PCB to the 3 wires that will allow it to operate (12V, Ground and J1850 data bus). We can choose the cheap option (3 wires from the PCB to some part of the harness) or the expensive one (ref# 68811-07 HD harness that comes with the tachometer ref#67182-07).
Let’s go first to take a look on the schematic (spedometer side) to understand what do we have there:

As you see, there is a harness that goes from the speedometer through the 39A/B connector to a subharness and from there to the HD main harness through the 20A connector. This connector is located just under the fuel tank, as seen in the following pictures.

The objective is to connect the wires to the bike in a way that it is not altered, this means it can be undone. So, this choice only gives me a solution..to make a subharness that will be connected between the connectors 20A (33482-1210) and 20B (33472-1210) and to leave a new connector in a more accessible area. This will allow me to unplug easily the tachometer without the need of removing the fuel tank.
Next image shows the schematic of what I had in mind, this way I was able to understand how many wires and connectors were needed..

As you see, 4 subharness will be needed. 2 (AUXILIAR HARNESS i MAIN HARNESS) will be connected to the bike and the other 2 (TEST HARNESS i REPRO HARNESS) will be used when needed in case I want to test or reprogram the PCB. Following sections will detail the pinout of each one of the subharnesses.

TACHO PCB CONNECTOR

This is the pinout for the PCB DB9 connector. In hindsight, it would have been better to use a different type of connector..but, with the housing already printed it was not possible to change (basically I didn’t want to spend more time..).

MAIN HARNESS

This harness will allow us to bring the 3 needed wires from under the fuel tank to a much accessible part close to the handlebar. Furthermore, there will be an extra connector that with a MAX232 or similar, will allow us to broadcast messages from the J1850 data bus to the computer and to use it as a datalogger.

Pictures taken during the harness assembly. As you see, a 2A fuse was also included to protect the bike in case an internal shortcircuit.

The connectors used to connect both harnesses (image below) were in my miscellaneous box.

AUXILIAR HARNESS

This harness will allow us to leave the bike in stock condition. The idea was to create a kind of “man in the middle” harness to be in between 20A/B connectors.

Find below the reference tables for each one of the connectors.

Find some images during the connectors assembly:

Watch this youtube video in order to learn how to assembly and disassembly Molex connectors.

TEST HARNESS

This harness was very useful during the code development phase. It allowed me to test new code improvements very easily. It is basically a connector that goes directly to the DLC(Data Link Connector) and another that goes to the PCB.

REPRO HARNESS

As before, this harness allowed me to connect the PCB directly to the pickit in order to reprogram new code.

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