GSRCRXsi

sorry if this is in the wrong area, i didnt really see a general wiring section, and this section seemed the best to ask this kind of question.

alright, so i have a 91 CRX with a b18c motor obd1 (p28 chipped running crome) that is my track car. there have been lots of things added and removed from the wiring over the years and its beginning to get messy. i want to rip it all out and just start fresh. this will give me the opportunity to remove anything that is unnecessary for a track car, and add things to the wiring.

i am having someone make me an engine harness with a firewall connection. my goal is to somewhat separate the engine and chassis harness to simplify it all, and to clean it up. the guy building the engine harness is going to wire in a plug on the inside of the cabin to output signals that need to go to the chassis/cluster. i am going to rewire the chassis myself to accommodate the new engine harness. i do not want to hack up the new engine harness so having a plug to wire up to will be great.

sensors i do not have:
Knock Sensor
HO2S (use a PLX M300 for wideband)
Oil Pressure Switch
EGR
IAB
EVAP

so looking quickly at the engine harness as it is, im trying to build a list of all the things that i will need outputted to a plug.

what i have so far:

1. D14 - O2 signal (will wire in PLXM300 signal)
2. D04 - SCS Service Check Connector (will be wired to a switch for easy code checking)
3. A13 - MIL or "CEL" light signal (for CEL light on cluster)
4. B10 - VSS signal (for speed on cluster)
5. B01/A25 - 12V power (to power ECU)
6. B02/A26 - Ground (ECU will ground through on-harness T-stat ground, but good to have a ground available to tap into)
7. D02 - Brake Switch ??
8. A07 - fuel pump signal
9. B09 - starter signal should be a straight shot to pin B09, and not splice into #10
10. BLK/RED or BLK/WHT wire from starter solenoid plug (not the post terminal)
11. BLU wire from distributor - Tach signal (for tach obviously)
12. YEL/GRN wire from ECT sending unit (for water temp on cluster)
13. WHT/BLU wire from ALT 4-pin plug (for charging system light on cluster)
14. BLK/YEL wire from ALT and VSS (power supply for these)
15. BLK/YEL wire from distributor (main power for spark)

so what else has to be outputted to the chassis/cluster from a stand alone engine harness?

TrueNorthStar

Oil press. switch

then of course from the chassis:

High beam
fuel level
turn signals
dimmer input (lights on/lights off)


Kinda doing the same thing on my 91 crx, but i have a motec and a aim sports dash, heheh the "CAN" bus is soo cool.

GhostAccord

What sensors/solenoids are you keeping / removing? It's hard to say what you can and can't remove, best bet would be to talk to your tuner and see what you can run without.

Just off the top of my head here are a few things you will need to wire, this depends on your tune and parts.

ECU inputs

TDC / CKP / CYP Sensors
MAP
ECT - This is not the sensor on the Tstat or water neck, it is usually located in the head under the distributor.
IAT
TPS
HO2S (Primary O2 sensor)
VSS
VTEC Pressure switch (if applicable)
Starter signal
ALT FR signal
Brake switch signal
Battery Voltage (IGN. 1)
A/C signal (if applicable)

The tach or RPM signal does not go through the ECU. It goes from the distributor to the gauge cluster. However you will need this.

ECU outputs/control

Fuel injectors x4
PGM-FI main relay (fuel pump)
MIL
IAC Valve
A/C Compressor Clutch relay (if applicable)
Rad ran Relay
ALT
ICM (ignition control module)
HO2S heater
VTEC Solenoid valve (if applicable)

I may have missed a couple......These are the basic I/O pins for an ECU. Some can be removed depending on tuning. Someone else can chime in on all the gauge cluster and chassis wires.

GSRCRXsi

I have all the normal sensors you would expect on a b18c motor except the knock sensor and the o2 sensor. I have a PLX M300 wideband that I use for tuning. Both the knock sensor and o2 sensors are disabled in crome.

I don't need to know what sensors I need to keep on the engine. I'm good there. What I need to know is what sensors need to be crossed into the chassis harness from the engine harness. So I can tell the harness builder what signals to output to a plug (which will connect to the chassis harness I am going to build myself). I explained all this in my original post.

GSRCRXsi

Thanks truenorth. I do not have an oil pressure switch, I have an oil line to my sender for my oil pressure gauge in that spot. Thanks for reminding me of that though.

GhostAccord

Wouldn't all of the wires for the sensors that you are keeping be required to be crossed into your chassis harness?

Sorry I can't be of more help, I don't fully understand what it is that your looking for. Hope someone understands and can help you out.

GSRCRXsi

well dont a lot of the things just need to go to the ECU? like this stuff: TDC / CKP / CYP Sensors, MAP, ECT, IAT. these are sensors in which there outputs go to the ECU and no where else on the car. what im wondering, is if there are any other sensors in which the output needs to go somewhere else OTHER than the ECU.

like the stuff i listed, the Tach signal comes from the engine and needs to go to the chassis to the cluster, and the VSS goes to the ECU and the cluster, it it needs a separate output too, and so on. im just wondering if ive left out anything.

my ultimate goal is to have 2 main harnesses. one for the engine, one for the chassis. connected by one plug (or two or whatever, but in one location) under the dash for signals that need to cross over. hopefully that clears things up.

GSRCRXsi

I have updated the first post with some more/updated information. after looking at the Helms for a looong time cross referencing things that would need to come off the engine harness and out to the chassis harness.

the only thing that i dont know that NEEDS to be there is #7 and #8.
#7: is the brake switch crucial to the ECU? why does it need it? i thought the brake switch was just for the tail lights...
#8: is this only for the AC system? or will the rad fan be solely controlled by the Thermostat switch?

ef92b

you missed the ff:

A07 - fuel pump trigger to main relay ; green/yellow wire
D22 - must be paired with B04
B09 - starter signal to main relay; attached to under dash fuse box ; blue/white wire
under dash fuse box to Alternator and VSS Supply; black/yellow wire

with ef's and crx's, the thermostat switch solely controls the rad fan but any 92+ teg/civic/accord/prelude wiring diagrams, same thermostat wire is tapped with A12. see diagram below. you can always have the ecu turn on the rad fan at what temp u prefer compared to the stock thermo switch which triggers at 93 deg C. i set mine at 86 deg C. it's been set like the past 5 years.



below is the ef/crx diagram which i moded a bit and been using for years while constructing custom harnesses for my customers.

GSRCRXsi

thanks for the reply. i have a few questions.

A07, could this be left empty and just wire the relay to a switch to ground to power the fuel pump?

D22 connected to B04, why? D22 is a signal ground for a few sensors on the engine, B04 is some connection for the TCM, which my manual says is for A/T. i have a manual transmission... even so, this would be something within the harness, and not need an output for.

B09 starter signal, can this be left out? why does the ECU need this? it isnt controlling anything with the starter according to the circuit diagrams.

alt and vss power supply (BLK/YEL), thanks ,i saw that in the diagrams today and meant to add it. i also need a BLK/YEL wire for the distributor power supply correct?

i have updated my original post again. still confused about the brake switch. do i need it?

ef92b

A07, yes you can leave this and have it done as you've mentioned but as per OEM functionality, when wired to the ECU, whenever you turn the key at ON position, the fuel pump primes fuel for 2-3 seconds. this is through A07. then as soon as the engine's running, A07 continues to trigger the main relay for continues pump operation.

D22/B04 - i'm sorry, that was a typo error. should be paired with D04 whenever you jump a wire while checking your MIL/CEL.

B09 - try to trace how the main relay functions. while you try to start the engine (key at IGN2, cranking position), the B09 being an input, signals the ecu a cranking signal is happening. I have really no concrete evidence in this to be honest but i always want to do things by the book/wiring diagrams. i've seen a lot of cars not having this wired in and it works so am in awe as well.

regarding the brake switch, for years i haven't really known it's function why the ecu needs it but i always wire it in. again by the book i'm guessing that whenever you step on the brake pedal, the ecu reduces the engine's rpm so the brake system works less to slow down the car or probably triggers another event via other output sensors like iacv, etc.

oh yeah, i completely forgot about the distributor's supply. also the blk/wht wire towards your starter solenoid w/c is also chassis to ecu harness integrated. both are AWG 12.

GSRCRXsi

thanks,

i removed the rad fan relay, harness guy said it wasnt needed.
had him wire in the fuel pump signal anyway, but i probably wont use it.

you can ground D04 anywhere for the CEL signal, doesnt have to be to D22. i have mine setup to a switch now, and it just grounds to the fusebox mount under the dash.

thanks for the help.

ef92b

you're welcome

regarding the rad fan relay, your harness guy might not know it but your tuner will ask for it for sure. why i prefer to wire this in always? if the thermo switch gets busted, i don't need to replace it. i simply use it as a backup switch since i let the ecu control when the rad fan turns on, lower(84-86 deg C) than the thermoswitch w/c is @ 93 deg C.

on most H22 engines' harness i build, i use the ecu to control the fan instead since our local honda dealer does not have a replacement part for the thermo switch. the faulty thermo switch is there but simply a dummy plug. have it wired

GSRCRXsi

in all honesty im not too worried, ill probably just wire it up independently to a switch like the fuel pump.

so you were saying #10 and #15 need to be 12ga wire?

ef92b

yep, awg 12 it is. both will need all the juice your battery can provide.

and since you're rebuilding your harness, adding a wire or two for the fan relay and brake input line won't hurt.

eg6madness

interesting i was just about to make a post about similar, hope you dont mine me postin in here and asking a question or 2 .

I am doin the same for a OBD2a harness. after looking at the harness, pretty much most if not all of it runsto the ecu plugs. how ever i have a few wires that seem to come from the driver side and runs through the chassis harness to the ecu. here is the list

a11 - yellow and black - power source
a24 - yellow and black - power source
a10 - black - power ground
a23 - black - power ground
a9 - brown - logic ground
a22 - brown - logic ground
a12 - blue and black - iacv
a17 - black and red - ac controller
a18 - green and orange - mil
a16 - green and blue - fuel pump relay

c18 - blue and white - vehicle speed sensor

d5 - green and white - brake switch

i wouldnt be using ac so that is out and the brake switch .

can i just ground the "power grounds" to any place on the chassis ?
where do logic ground come from/go to ?
for the iacv , can i just run the wire from the iacv straight to the ecu ?
for the vss, can i do the same and split it to the cluster and the ecu?
and for the fuel pump relay how do i wire that back into the car's main relay ? ( the car was carbureted so i now have to make a harness for it, i will be using an external pump now)

is there anything you guys think i am missing that runs through the chassis harness that i need to get the motor to start and run?

The car is going to be a race car so the less harness the better and i am running a hondata.

poorsupra

i know its an old thread, but the information is incomplete. i am currently doing a carb to efi conversion on my 86 civic dx. my goals were to make a "engine harness" and a "chassis harness" to run my obd1 d15b vtec almost completely standalone from the stock chassis wiring(obiviously besides a few spots where the harness tie in together)

just looking for any insight from 2013 honda-tech!