View Full Version : RB25det engine bay fuse box
yes its more fun fun rb25det wiring :rolleyes: Today million dollar question is what are the 2 plugs attached to the side of the fuse box?
The people who sold me my engine have chopped the loom coming out of the fuse box and looks like they have integrated any relays/fuses into one big loom. They said it was already all wired to hook up.
So whats the go with the plugs? Cos I got the other ends hanging off a loom coming off the engine.
26-05-02, 02:47 PM
I take it you're converting an RB25DET into a car that the engine did not come in...
If so, there are only two looms you need, forget everything else.
The main loom does injection, spark, CAS, AAC, FICD, TPS, EGO, AFM, adjustable cam timing and maybe a few other things. The second loom you can cut up because it is the battery +12v thick wire to the starter motor, you'll probably need that and it also has the knock sensor wiring that plugs into the main loom.
thanks dude, I am getting there, a few more wires and some fuses and I think she be right :)
I looked at meggalas site (your a legend meggala) and got the pin outs and wiring diagram, there is a wire the goes from "F" on the ignition switch to pin 49 I think it was, whats this pin do? I am not sure where it should come out of on the key thing, should it be providing 12V when the key is in the "off" position?
26-05-02, 05:54 PM
Pin 58 is the unswitched +12vdc for memory backup of the ECU
49, 59, 109 are +12vdc ignition. That diagram on meggala's site for the power circuit is somewhat confusing regarding the +12v supply to the computer.
I wired the ignition straight to a relay that switched a fused 15A 12v supply to 49, 59 and 109.
Connect a constant 12v to pin 58
hmm i connected the ignition straight to pin 45, I will tkae your advice on the 49,59 and 109. When you say constant 12v to 58 is that just connected to the battery?
Cheers Bozz your being a great help man :)
Whats the go with pin 43? it is connect to P or F or something on the diagram, the pinout says that 43 is the start switch. So whats th go with what its connected to?
28-05-02, 10:26 PM
Pin 43 is from the start switch on the ignition barrel - it tells the computer to enter it's engine start routine - ie much longer duty cycle for injectors to compensate for the lower voltage and low RPM etc...
See this is where I am running into trouble, at the back of the barrel I have identified the following wires: ignition, accesories, constant 12V, starter and ground (not sure about the ground one). And thats all the wires there are :(. Wouldnt the start switch be the same as the ignition wire?
(scuse me if I am being stupid, getting confused :()
29-05-02, 08:49 AM
No - The start switch is the wire that goes to the starter motor solenoid to start the engine :)
The ignition wire supplies 12v to the computer to enable it to run the engine - the ignition wire has 12v on it when the switch is in both ign and start positions, otherwise it is off.
sweet, thanks bozz, should be able to work some more of it out now :)
Todays minor break through: I have power to the ecu,
after a bit of fiddling and and relay logic I have found that the little red light on the ecu now goes on, alhtough to do this I had to cut the wire from the pin labelled ECCS coil ground and actually ground the wire from the relay, hope this doesnt effect anything in a bad way. Also whoever wired the cu before the engine came made it so the ecu was on all the time, I rewired it so that it comes on when the ignition is switched on.
Now the problem I am having is that there is no signal coming out of the fuel pump relay power to switch the fuel pump relay on.
30-05-02, 06:14 PM
The fuel pump output is actually what is called a current sink input.
What that means is you need a relay with one side of the coil to have +12v on it from the ignition switch (pin 49, 59 etc) and the other side of the relay coil attached to the current sink input(fuel pump wire from ECU). What it does is has 12v on the "output" when the fuel pump is off, then it pulls the 12v down to ground to energise the relay to switch it on, consequently switching the fuel pump on.
Fun isn't it :)
Just for condolences, all the wiring took me about 15 hours total... Now I could most likely do it all in 3-4 hours :)
ah ok I get it, cos I have one side of the coil grounded and was expecting a voltage out of the fuel pump wire to shut the switch. So I need one side of the coil connected to 12v and the other connected to the fuel pump relay wire of the ECU.
Damn why couldn't they just make things easy :)
31-05-02, 06:10 PM
When you wire it up, ensure the relay has a back-EMF protection diode and ensure you connect it correctly or the relay may blow your ECU up, a relay without the diode may damage the ECU when it turns off - it is a coil of wire and can generate quite a substantial spike when electricity is removed, the ignition coils in cars work on the same principle.
Unplug the relay from the socket and using a multimeter on diode check mode, one direction will read open circuit, the other direction will read between 0.4v and 0.7v. When you have the RED (Positive) multimeter lead on the terminal, that is the wire that connects to the ECU. If you connect it the other way you will force 12v into an ECU that is trying to pull it to ground - Smoke and sparks :(
hmm this sounds bad, I have a few spare relays from skyline fuse box, should these do the trick? I will diode test them.
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