Explorer Addendum

As far as I know, Explorer-specific wiring information was never released to the public (or dealers). The information presented here has been gleaned from communications with Explorer owners.

There is other information about the Explorer scatter around this website. Use the search tool (upper righthand corner) to find it.

It appears that two distinct Explorer wiring versions were produced. The late version had an Easy-Start box located under the seat. The early (pre-2014) version had a battery below the headlight mask, and a capacitor under the seat.

Explorer Battery

The battery comprises ten 2400 mAh Ni-MH (nickel metal hydride) cells in series. Each cell is nominally 1.2 volts, and typically exhibits a fully-charged voltage around 1.4 volts. Measuring the individual cell voltages can help determine battery health.

Connector wire colors are:

RED, battery positive.
YELLOW with GREEN stripe, battery negative.

Use of these cells surprised me. Ni-MH is not very tolerant of an overcharge, and OSSA had them connected constantly while running.

Four lithium-iron phosphate (LiFePO4) cells is series would be a safer choice. That chemistry is considered “equivalent” to lead-acid in terms of tolerance to overcharging.

Explorer Ni-MH battery back

Explorer battery connector

Burned Explorer ECU and wiring harness connector

ECU Failure in Early Explorers

Unfortunately, there have been several ECU failures documented in early Explorers. The ECU connector melts near pin 3, and also destroys internal components.

Pin 2 is a no-connect. Pin 3 is a stator winding for fuel pump power (and where the damaging current flowed). Pin 4 is the injector low-side switch.

My supposition is that although the high-current battery may not have caused the failure, it possibly contributed significant energy to the failure.

I am not aware of any ECU failures in the later (Easy-Start) Explorers.

ECU Postmortem

A postmortem was conducted on two failed Explorer ECUs. In both cases component F601 was vaporized. This part is a Rohm SP8K22 dual N-Channel MOSFET typically used for low-side switching.

Transistor 1 connects to ECU port pin 21 (this has no connection to the wiring harness and is undocumented).
Transistor 2 connects to ECU port pin 22 (“Testigo Averia” which translates as “Fault Witness”. I call it the Check Engine Light. This is a no-connect on the trials models, but may be part of the dash panel on the Explorer.

This was a surprising finding because the burned ECU connector pin was pin 3, the stator winding for fuel pump power.

The original 2011 wiring diagram shows one side of the CEL going to the ECU pin 22 (which is the MOSFET that exploded). The other side of the CEL is shown connected to ground. So nothing would happen when the MOSFET conducts. If, however, the other side of the CEL was connected to +12 volts instead, then it could illuminate.

The 2014 wiring diagram shows the Testigo Averia (fault witness) being part of the Conexión Cableado Homologacion (homologation wiring connection). But I have never seen a drawing for that harness.

F601 Vaporized PCB traces

F601 Exploded

Credit: Rohm Semiconductor SP8K22 datasheet

Key Switch

Think of the key switch as a SPDT toggle switch.

The key switch has 3 connections with wire colors as follows:

BLACK, the common terminal goes to system common / chassis ground.
YELLOW with GREEN stripe, this terminal is for Battery Negative.
WHITE with BLACK stripe:, this terminal is for the ECU kill-switch input.

Note that late-model Explorers have an Easy-Start system instead of a battery. In these models, the yellow/green wire is omitted from the key switch. Please refer to the section titled “Easy Start” on this website for more information.

Key switch physical wiring

With the key switch in the STOP position, the ECU's kill-switch input is grounded, thus preventing the bike from running.

With the key switch in the RUN position, battery negative connects to chassis ground thus completing the circuit. This puts the battery in parallel with the 12-volt (nominal) bus.

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