MoTeC Global Forum

Good Morning everyone. Being that many of you have several MoteC products in your race vehicles I would like to know where are you gentleman getting you 12V and ground for your devices. Pictures of installations would be helpful.

I read in the manual that the C125 could be connected with its own switch and a 5V inline fuse directly to the battery as to avoid having to switch the car on to program the dash? It is also mentioned that its best to provide a "direct connection to the negative terminal"

My question really is: Are you folks running a dedicated ground wire to the battery and one for power?
There are many grounding points under the dash of a car and several switched 12V wires inside also.

I am looking for some advice and best method to do this.
In my car for instance, there is a grounding bolt which "connects or conducts" to the battery negative terminal - I used a multi meter to test. To me that counts as a direct path - or no?

Hi,

The wiring layout in the manual is a recommendation, but it can be changed to suit your vehicle. I would always retain some for of fuse protection on the circuit (fuse, circuit breaker, PDM) to protect the dash from over current/voltage events, but how the power for it is switched in up to you. Some people just want all of the car to turn on at the same time, and others want to be able to individually power separate devices. With the Ground, it is better to run the grounds back to a common source and then to the battery, but isn't critical. The main thing to ensure is that there are good, clean connections for the grounds.

Dear Stephen,

so from what I am understanding the most important thing to consider is the ground point. I am guessing that when you say "clean connection" you mean properly connected or fastened in case of going into a factory grounding point on the chassis.

Correct, most of the issues that we see are related to a lack of a good ground, in this I mean that it is free of paint and rust, doesn't have any silicon or other contaminants under the connection point, and that there is enough surface area to allow for minimal resistance through the point. you need to make sure that it is tight so that there is no movement in the connectors.

The power supply also has to be good, so proper connectors and crimps, secured to avoid strain on the connectors, strain relief on the crimps and connector bodies by using adhesive heat shrink, and a reliable supply that will avoid spikes and dips as much as possible.

Thank you!

I am in the middle of my install at the moment. I am remounting all my main electronics on an alloy panel behind the glovebox (Which I have cut the back out of, hidden away but still easy access) where they used to be scattered around the car.

What I was planning to do was to get a heavy gauge cable (Same as the PDM supply) which will be connected to the chassis near the battery at one end and to a small bussbar near my electronics at the other. That way I can ground all the important stuff to a common point that should be at a very low resistance to battery negative/chassis ground.

I am using 18 AWG wire for my ground. In the past I have used 10 AWG but I am not sure we really need that thicker of a wire.

Not familiar with the wire size from the PDM.
I was thinking of getting a relay holder for the Wideband controller and C125 and also mount them somewhere behind the glove box. I think however I am going to just use fuse holders and get power from a switched 12V source inside the car. Then ofcoourse ground everything to the same point.

I am trying to build a mini harness to do this power and ground distribution. For the time being, I only have 2 items to power and ground. If I ever get an extension box or something else I may have to go the panel route.

please post photos.

I have not got photos yet apart from a quick snap of the roughed out mounting panel to send to a mate. Motec recommend a #2 0r #4 battery positive for the PDM, I am thinking #4 given I have a PDM30 so lower current capability to begin with. I may go much lighter than that for the ground to the bussbar but given I want to ground my PDM to it the cable should be able to support current dumps from the likes of the wiper motor without any meaningful voltage rise on the bussbar.

The basics of my setup, this is just a rough out with some scrap sheet. (Forgive me, Motec guys, the E11 will have to cohabit in there for a while yet until my budget recovers from the C127 and PDM!) I plan to bring in a ground cable to a bussbar on the right side of the alloy plate to have the ECU, Dash, PDM and current UEGO controller all grounded to a single point. My UTC and UEGO controller will also be permanently mounted here, there is just enough space.

That looks cool. What does the PDM do?
So you guys get rid of all the factory relays and ecu's etc?

Yeah, basically control of all power in the car. About the only thing that wont go through it is the main starter motor current (For obvious reasons of hundreds of amps!)

The only relay I may end up refitting is the stock windscreen wiper control relay for my car as it is used to reverse the direction of the wiper motor to park it. There is an eccentric cam in the motor assembly which changes the arc the wipers run through when the motor is reversed and parks them low down off the glass. Only if I can work out the control logic and make it play with the PDM without too much messing around.