Wiring the Megasquirt II

The rest of the wiring relating to this can be found on the truck electrics page

An ECU Control Relay from a Conquest/Starion will work with Megasquirt. A control relay from a DSM should too but there are many more terminals coming from the DSM relay.

This is the relay but it wasn't intended to be outside so it was sealed up with silicone.

Get about 10 inches of the wires after the plug so there will be plenty of length to splice and attach to the new connectors, fuse bank positions and other relays.

There are 8 wires all different colors.

From top to bottom their color and control relay position according to the C/S service manual and a short description.

BW-black/white stripe 01 / (+) output / turns on the Fuel Pump when starter is cranking or engine is running

WR-white/red stripe 02 / (-) input / signal from ECU to activate fuel pump relay after

ign. switch moves from "start" position and engine is running

BR-black/red stripe 03 / (+) output / when ignition "on", this sends power to the injectors

B -black 04 / (-) grounded to body

BY-black/yellow stripe 06 / (+) input / from ign. switch "start" position

this activates a relay that turns on the fuel pump

R -red 05 / (+) output / when ignition "on", this powers the ECU

L -blue 08 / (+) input / from ign. switch "on" position

this activates a relay that powers the ECU and the injectors

B -black 07 / (+) input / fuse link back to Battery positive terminal

Here's the pigtail from the control relay.

The "control relay" is actually two relays ( magnetic coils ) in one and how the control relay functions is that when the ign. switch is in the "on" position that energizes one of the two coils via position 8 (14ga) and that takes the current coming in from position 7 (16ga) and passes it through to positions 3 and 5. When the ign. switch is in the "start" position that energizes the other coil to pass more of the current from position 7 through to position 1. In a Conquest/Starion there are many connections that branch off from the control relay that we don't have in our MSII wiring. In a C/S this current comes into the relay from a single 16ga wire. We will do some swapping of wires on the connector we have and use one additional relay for the fuel pump/coil.

There are 4 wires to swap

-Swap the blue wire and black wire in the connector positions 7 & 8. This will upgrade the battery feed from 16ga to 14ga. 16ga in a non-engine compartment setting is rated to 22amps but a 14ga wire is rated to 30a. These wires are being used in the engine bay (much heat) and that lowers the rating of the 14ga wire to 16amps. Position 7 will now be able to pass through a little more current to #3 & #5.

-Swap the wires in positions 1 & 3. Position 1 is black with a white stripe and position 3 is a black wire with a red stripe. This will give us a wire large enough to be used to power the 4 injectors through position #3. The smaller wire that was moved to #1 will be used to power an additional relay for the fuel pump and ignition coil and this relay will get current from sub link 2, #2. In a C/S the load from the ignition coil comes from the ignition switch (which was the blue wire in position 8 that we moved to position 7) but moving the current to the additional relay that is common with the fuel pump will give MSII the ability to deactivate them through the control relay in the event of an engine stall. Position #5 will power the distributor, the MSII ECU, the heater in the 02 sensor and will have one spare fuse location. Position #3 will supply power to the 4 injectors.

Here's how we use the control relay with Megasquirt

(16ga) BR-black/red stripe 01 / (+) output / to activate the additional relay that will power the fuel pump

and ignition coil. This new relay will go to two fuse bank locations: one 10amp fuse

to the Fuel Pump (+) and one 10amp fuse to the ignition Coil (+) terminal.

(The ECU will still cut fuel and ignition to this relay through the control relay if the

engine stalls and when wired this way will not put the load on the wire in position #7.)

(20ga) WR-white/red stripe 02 / (-) input / signal from the MSII ECU to keep the fuel pump/ignition coil activated

after the ign. switch moves from "start" position and engine is running.

This is Megasquirt pin #37 and is the wire in the harness tagged "fuel pump".

(14ga) BR-black/white stripe 03 / (+) output / to 4 fuse bank positions: one 2amp fuse to power the Magna

Distributor, one 2amp fuse to supply the power to the MSII ECU, one 5amp fuse to

the 02 heater and one spare fuse location.

(20ga) B -black 04 / (-) ground

(14ga) BY-black/yellow stripe 06 / (+) input / from ign. switch "start" position

this activates a relay that turns on the fuel pump/ignition coil relay

(16ga) R -red 05 / (+) output / to fuse bank, two fuses: both 5amp to power the 4 injectors

(16ga) B -black 08 / (+) input / from ign. switch "on" position

this activates the control relay

(14ga) L -blue 07 / (+) input / fuse link (sub link 2, #2) back to Battery (+)

There are 4 fuse banks and each has 4 fuse holders:

amps/purpose / power feed from

BANK 1

10a Fan #1 Motor sub link 2, #1

10a Fan #2 Motor "

10a Fan #3 Motor "

02a Fan Control Relays sub link 2, #2

BANK 2

05a 02 Sensor control relay position 5

05a MSII ECU power "

05a Injector 1 control relay position 3

05a Injector 2 "

BANK 3

02a Magna Dist. control relay position5

00a SPARE "

10a Ignition Coil pump/coil relay

10a Fuel Pump "

BANK 4

00a SPARE none

10a Pump/Coil relay control relay position 1

00a SPARE "

Each fuse holder comes with 4 separate terminals and one strip of 4 that can be cut into 4,3 or 2 depending on your requirements. The terminals only go in one way correctly but can be inserted wrong. The terminal has a small arm off each side you can see in the middle photo. Those fit between the sides of each cavity and keep they from moving around. You can see in the below right photo the terminal in the top/left position will not go into that hole and the one in the lower position does and how the two arms keep it centered.

The terminals will hold even the small 20ga wires that come in the MSII harness. They will also accommodate 14ga wires. They crimp on just like the GM style terminals and you can use the same crimp pliers.

Different stages in crimping.

Terminals push in and lock. Don't make all the wires the same length keep them different so they will not bunch up. These were cut to length before the terminals were attached with their positions in mind.

The 4-terminal common buss, cut apart as needed.

There is an unused plug in the firewall to route the harness into the cab. With all the wires located to their positions and double checked then they were cut to length and the terminal ends attached.

Fuse holders mount to a stand under which the wiring has a place to converge. Relays and the fuse link holder fasten to the fender apron.

Mounting brackets cut to fuse holder shape, fit and pulled removed along with the fuel rail for powdercoating.

All those wires routed, wrapped and secured to fit under and in-between the mounting stands.

Powdercoating: items near the battery don't like the acid/fumes.

Trivia -Did you know that in the Conquest/Starion the covers for the relay box beside the battery were factory coated?

The Fuse link holder receives a new connector

there are a few extra fuse locations the open connector is for the horn relay