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Author Topic: DIY LS1 harness mod instructions for dummies.  (Read 13369 times)

Offline danzan

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DIY LS1 harness mod instructions for dummies.
« on: May 10, 2010, 06:55:51 AM »
Non dummies will find better ways to do some of this stuff, but this works.

This is a basic mod for the 1999 - 2002 LS1, that will get everything needed for a running car.  It does not address the different emissions requirements of the various government agencies or things such as dual fuel pumps or cruise control.

Here are links containing the 1998 info.  http://www.ls2.com/boggs/torques/98pinpcm.htm

http://www.lt1swap.com/98-02_ls1.htm

THIS IS NOT A "PLUG & PLAY"  You will be pulling wires out of the LS1 harness,  extending some of them, adding resistors, soldering & splicing LS1 wires to your FC/FD wires.

For a "plug & play" harness mod, i recommend that you go to Pez.

It is convenient to pull the following wires out of the camobird connectors

...C100...black 10 pin connector.
............H- dk blue (high fan)
............J- dk green (low fan)
............C- dk green (A/C status), B-dk gn/w (A/C clutch relay control)

...C101...grey 10 pin connector.
............D- dk green/white (fuel pump relay control out)

...C102...
............A- purple (starter solenoid "start" power in)

...C105...black 8 pin connector.
............G- white (tach signal out)

Blue 10 pin....DkGrn/W (A/C request)


There are 5 pink wires going to the F body external connectors.  cut those wires off to equal length & skin about 1/2" of insulation.  Twist the ends & solder them together, along with an extension wire.  #10 wire will do for the extension.  That wire will go to the ignition-on wire at the ignition switch.

There are two orange wires on the F body external connector.  Those wires will connect to battery constant.

After you do these power wires, you can cut off the F body external connectors.

There is one very long bundle that has a rubber grommet on it.  Be careful when you cut that bundle off, because there is a loop of orange wire, that comes out of the fat harness shroud, at the top end of that bundle.  There are no needed wires in that long snake.

You may want to save the long wires, for use later.

4.  Solder a 470 ohm resistor in the red wire coming from pin 15, red connector. 

5.  CAGS-  Cut off the CAGS plug from the harness.    Solder a 2.2K ohm resister between the  two cut wires.

BLUE CONNECTOR WIRES.

1.  Fan control, low temperature-dark green wire coming from pin 42, blue connector. 

2.  OBD2.  Dark green from pin 58 blue ?serial data?. 

RED CONNECTOR WIRES.

1.  Speedometer control-Skin about 1/2 inch of insulation from the purple/white wire from pin 21. red connector. If you are using a smart speedometer, the purple/white wire goes to the speedometer input.       

2.  Tachometer.  White wire on pin 10, red connector. 

3.  Fan control- High temperature.  Dark blue wire, pin 33. 

4.  Starter-Use the purple wire already in the harness.

5.  Oil pressure.  A wire must be added if the Mazda gray/red wire is missing.  One end will go to the gauge.  the other end will go to your sensor.  This wire will come out of the harness at the location of your sensor installation. 

6.  Coolant temperature.  A wire must be added.  This wire will go from the sensor location @ the threaded hole at the rear of the passenger side cylinder head, to the gauge. 

7.  Check engine light.  Use the brown/white wire from pin 46.

8.  Fuel pump relay.  Dark green/white wire coming from pin 9, red connector. 

9.  Back up lights.  Not controlled by the PCM.  connect one plug wire to ignition-on, & the other to any red wire, that goes to the lights.

10. Reverse lockout-automatic only- light green, pin 44 , red, if you are lucky it will be there

GM A/C

11. A/C request.  Dark green/white-pin 17

12. A/C status.  Dark green-pin 18

13. A/C clutch.  Dark green/white-pin 43
« Last Edit: June 30, 2012, 10:14:12 PM by danzan »
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Offline danzan

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #1 on: May 10, 2010, 08:48:29 AM »
i just got a PM ?? re: the CAGS 2.2k resistor & alternator 470 ohm resistor.

CAGS is "computer assisted gear selector"  commonly called "skipshift".  it was a feature to force a shift from 1st gear directly to 4th, on low to moderate acceleration, to save gas.

skipshift is normally engaged, so if you just remove the plug, it is disabled.  however, the PCM will send a DTC, & light the MIL.  the 2.2k resistor fools the PCM into thinking the solenoid is still plugged in.

in the 1999 to 2002 f bodies, the PCM turns on the alternator.  in the 1998, the ignition turns on the alternator.  the alternator turn on circuit is designed for 5 volts.  the PCM puts out more than twice that, & that resulted in many alternator failures.  the 470 ohm resistor drops the PCM voltage to a safe level.  the resistor was not needed in the f body, because other circuitry dropped voltage.  you can eliminate the whole enchilada by replacing the regulator with part # D702SE.  that is a bullet proof upgrade, which eliminates the PCM control.

i had a DIY thread on V8rx7forum, on the D702SE mod, but it's gone :'(.  when/if i can find my pics, i will post the thread here.  i am not going to remove & tear apart my alternator to repost that topic.
« Last Edit: May 10, 2010, 08:53:01 AM by danzan »
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Offline digitalsolo

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #2 on: May 10, 2010, 09:09:52 AM »
Here is a link to the file Dan attached as a PDF as well:

http://www.ls1fc.com/pdfs/BasicHarnessMod.pdf

-Blake
Blake MF'ing McBride
1988 Mazda RX7 TII
347" Forged LS1/T56/PTE 76GTS/ProEFI/8.8 Moser SRA/Other stuff


Offline sunshineFC3S

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #4 on: May 10, 2010, 12:53:49 PM »
Dan,
thanks for posting all that up.  Regarding the 470ohm resistor for the Alt.  I stopped at radio shack and saw they had both a 1/4watt and a 1/2watt 470ohm resistor...which is the correct one to use?
Thanks again,
-Alex
'88 TII - LS1/T56 swap.
'06 Mazdaspeed6 VRM.
'91 TII - victim to car cancer, RIP
'06 Mazda3 - Sold.

Offline danzan

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #5 on: May 10, 2010, 01:06:52 PM »
Dan,
thanks for posting all that up.  Regarding the 470ohm resistor for the Alt.  I stopped at radio shack and saw they had both a 1/4watt and a 1/2watt 470ohm resistor...which is the correct one to use?
Thanks again,
-Alex

the smaller the better.  there is almost no current flow in that wire.  if they have 1/8 watt, i'd get that, but 1/4 watt is fine.
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Offline rcarson25

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #6 on: May 13, 2010, 08:24:04 AM »
Man, I wish I had this when i was doing my wiring.  Would have made my life a whole lot easier.   Great info here. 

Offline tweak

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #7 on: May 14, 2010, 06:48:38 PM »
Thank you! I know what I will be doing this weekend. :)
Red 88 FC GTU - 2000 LS1  - 3 stage 6 gallon dry sump - Stock LS1, T101A transmission - Stance coilovers .... lots of tires.

Offline danzan

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #8 on: May 14, 2010, 07:02:22 PM »
notice that i bypass all of the mazda relays for all of the engine functions.

new fuel pump relay. starter solenoid comes directly from the ignition switch. PCM constant comes from the ignition switch, as does ignition-on harness wires.

this enables you to make room in the large relay/fuse box for the front relay box functions.

see 65imp's large relay/fuse box pic, in his build thread.
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Offline svsgt1

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #9 on: February 01, 2011, 12:07:19 PM »
I have a Corvette harness (I'm fairly certain anyway) and there is a fuse block on that harness that has about 15 pink wires on it.  I don't think I have the Camobird connectors as per these instructions.  I'm assuming these are the power lines for all of the engine related items; coils, injectors, etc.  So do I just put all of these pink wires to a 12v switched source?  Do they need to be fused individually or can I group them together?

Offline svsgt1

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #10 on: February 06, 2011, 08:22:14 AM »
To answer my own question. I pulled apart my harness and each fuel injector is own its own circuit. That is why I have so many pink wires. I think I will group them like the fbody harnesses by bank.  Life was much easier once I decided to open up the harness and figure out what everything was.

Offline Yarp

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #11 on: February 06, 2011, 07:24:45 PM »
I think I will group them like the fbody harnesses by bank. 

Wouldn't that turn it back into batch fire?
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Re: DIY LS1 harness mod instructions for dummies.
« Reply #12 on: February 07, 2011, 09:43:17 AM »
No, it wouldn't be group fire as I'm just combining the pink wires (+12v) for each bank of injectors.  The ECU still controls each injector by grounding the wire of the injector it wants to fire.  The power wires will be common, not the grounded control wires.

Offline the burning giraffe

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #13 on: May 14, 2011, 02:00:41 AM »
i have a 2004 gto pcm and Im worried that It might be overcharging. It does have the 470k resistor in place, but Do i possibly need a higher one?

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Re: DIY LS1 harness mod instructions for dummies.
« Reply #14 on: May 18, 2011, 02:04:16 AM »
is it ok to use a 470k 1/2W resistor? Thats all I could find. Thanks!

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