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so i bought both the wiring fundamental and Practical Wiring - Club Level courses because i always wanted to learn how to build wiring harness from scratch for cars that only need standalone harness simple i have enough knowledge to do simple wiring things but the problem i have is that i dont now which wire goes where so i bought these two courses, and i dont seem to find the answer to my question. for example i use a maf sensor with 4 pin i am not sure which wire goes to which pin on both the sides the ecu and the sensor connector.
There are a few challenges before you can really create a wiring harness.
1 - You need to have the Pinout information for the devices (sensors, ECU). Exactly which pin is the ground, signal & power. To learn this information, you need the documentation from the manufacturer (data sheets, ECU installation manuals), but sometimes you have to get this by reading and figuring it out from a workshop manual wiring diagram. The ECU documentation should describe the available inputs / outputs on the connectors. If you can get some part numbers off the physical parts you can often search for those on the internet and find some relevant documents -- enthusiast forums and ECU vendors also sometimes have this info, so don't be afraid to ask.
2 - Next, you need to understand what the outputs can provide and what the inputs expect. For example, a two wire temperature sensor is usually a sensor that varies is resistance with temperature. Sometimes resistance increases with temperature (Postiive Temperature Coeffecient like PT100 or PT1000), or the resistance decreases with temperature (Negative Temperature Coefficient -- NTC common for many OEM temp sensors). Knowing the range of resistances or voltages produced will help you decide which input on the ECU a sensor should be connected to, or which power supply (5V, 6V 8V, 12V) on the ECU should be used. Your MAF sensor may have a resistive temperature element, and a square wave frequency output (this would typically be connected to a digital input that can measure the frequency on the ECU.
2b - It's not just sensors, you'll also need to understand the output devices - injectors, coils (possibly ignitors to trigger the coils), solenoids, relays for fans and fuel pumps.
3 - One big challenge can be finding mating connectors for your harness. OEM sensors can be tricky to source, and sometimes you have to revert to cutting up factory harnesses just to get connectors / wiring that you can splice into your harness. Often you can get connectors -- but only with pigtails installed from a dealer -- so that marginally better than starting with an OEM harness.
4 - To make it all work, you'll need calibration information -- again manufacturer data sheets are the best source for accurate info, but often aren't available for OEM sensors -- so you'll have to find this information somewhere, or develop a way to test / calibrate them yourself.
Hope that helps.
Well, there is no simple answer to your questions. Like David suggested, read some ECU manufacturer manuals, even if it's not the one you're gonna be installing. Most of the sensors and actuators use the same guidelines on how they function, like MAP Sensors usually have a +5v, and signal out and a sensor ground. But for Idle Air Valve, you could have a PWM or a Stepper Motor, which are not connected the same way. You will need to get the pinout of the sensor you are using (if you are buying them new, it usually comes with it) or if it's used, you can use the wiring diagram of the car to get the pinout, or last resort is a multimeter or oscilloscope. Some sensors like IAT of Coolant temperature, you don't even need to care about the polarity.
Here's a link to the Ecumaster EMU Black manual that is found online, of course there are some specific to this ECU in the manual, like navigating the menus and all, but there are also schematic on how to connect the various sensors and the signal they output. Same for the actuators.
Hope it helps,