MoTeC Global Forum

Hey guys,
We are about to completely redo the engine wiring harness with fresh wires and deutsch connector. What is the best wires gauge size to use?

We'll be using Mil-spec M22759 wires
signal contact : 22gauge
power contact: 18 gauge

Will be using Deutsch DTM connectors connect between the sensors and the M800 unit.

I wonder if those gauge size is good enough?

Please help.. = )

Also.. will using gauge 18 for signal and 16 for power overkill? Any issue maybe?

mr2andy wrote:We'll be using Mil-spec M22759 wires

That number is incomplete.

22759/xx

that XX is a number between 01-99.

M22759/16

Hey,
I have the unterminated M800 wire harness which uses primarily M22759/32-18. The Sync, Ref, CAN Hi and Low are the only devises that use the 22 gauge.

What about the +12v and ground wire?

I wonder what is the different between M22759/32 and M22759/16

M22759/16 = Tefzel
which is recommended by Motec??

I noticed after I posted that the Motec M800 manual recommends M22759/16 for the wire harness. Strange that the factory unterminated harness uses something different.
The question concerning the gauge wire for the 12v and ground is interesting too. Last week I was shopping for a mil-spec bulk head connector and the vendor asked me what gauge wires will be used. I did not have my harness with me so I called Motec East to find out. They told me that but for the ECU 12v, the two ground connections, the ref, syn, and can hi and lo, every thing is 18 gauge. They said the 12v and grounds are 12 gauge. When I got home that night I looked and the 12v and grounds are also 18 on the harness. The 12v 18 gauge wire runs to a large splice that includes roughly 10 18 gauge wires and one 12 gauge. In my harness design I have the one 12 gauge wire running to pin 87 on the injector relay. Pin 30 runs to my battery juction block. I just assumed that the power draw at the ECU was only such that it requires an 18 gauge wire. The two ground wires are similar in that they each have a large splce with about 10 18 gauge wires (but no 12 gauge). Whether this is right or wrong I really don't know. I just assumed that this is right since it is the Motec unterminated harness.

Hey buddy,
The harness you have is good!

The 12v 12 gauge wire you wired to the relay will supply power to the ten 18 gauge wires which will supply power to things like fuel pump, fuel injector, relays. The 12v 12 gauge will also supply power to the 18 gauge which supply power for M800. I'm sure motec know how much power M800 will be drawing therefore a 18 gauge to the M800 is sufficient.

If you look at M800 wiring diagram, M800 activate injector, fuel pump and etc by pulling to the ground, meaning the 12v supply to those parts are outside of the M800. What is important is the size of the ground wire. Now, if the way you activate your fuel pump, fan, and other items through individual relay, then you'll see light current going through the ground as well. Plus, there are two ground wire(A10, A11) so... two 18 gauge wires are almost equivalent to one 14 gauge wire(cross section wise).

Anyway... thanks for posting the information though.. you have help answer some of my questions as well!!!

Hey, thanks for your response - that confirms that I am atleast on the right track with my harness.