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LT Wiring Harness Modification

Page history last edited by Greg 14 years, 11 months ago

 

 

Modifying The LT1 Wiring harness

 

Modifying the factory LT1 wiring harness is not that difficult, if you have the proper reference material.

 

Several websites offer wiring diagrams and even modification services for those not willing or able to do their own modifications. 

There are several features of the factory harness that can be eliminated, and the end result is a stand-alone, functional harness.

This guide will provide the Hybridder with the resources to modify an existing harness themselves, or at the least, a starting point

for a cost effective wiring solution.

 

First, you need a wiring harness (most complete engines are sold with the harness and PCM):

 

 

Now you can start deleting the unnecessary sections: automatic transmission, EGR and air pump,

and the fuse block (if you want to use the Porsche fuse panel). Two of the four O2 sensors on later models

can be deleted, but will have to be removed from the PCM program (using a program like TunerCats).

 

Please see the following page concerning PCM programming. PCM Programming

A detailed view of harness connectors is shown here...

 

The following pictures show a completed harness, to give an idea of what needs to stay in place.

 

 

 

 

As far as the in-car factory wiring goes, all engine wiring can be eliminated. There are only 5-6 wires that need to be spliced into the

Porsche wiring harness. Depending on the year of your car, these splices are made at a 9 pin (pre-85) or 14 pin (85 up) connector

on the firewall.

 

An understanding of the GM and Porsche wiring diagrams is beneficial to modifying the LT1 harness.

Additional sources of information are the factory Porsche manual, available in PDF form

(http://www.cannell.co.uk/Manuals.htm), and lt1swap.com (http://www.lt1swap.com/index.htm).

 

The following illustrations show the various circuits of the LT1 wiring harness, the factory 944 wiring schematics, and even PCM pinout connections.

The LT1 schematics are from a combination of GM models, with only slight variations concerning accessories.

 

 

 

Below is a diagram that illustrates converting a 4 O2 sensor system to 2 sensors...

 

 

 

GM LT1 Cooling Fan Wiring...

 

 

 

Ignition Circuit...

 

 

 

 

 

The IAC...

 

 

 

And now the 944 schematics...

 

 

The 14-pin underhood connector (85 up)...

 

There are only a few connections that need to be made here:

 

Blue / Yellow = Temperature Sender

Blue / White = Oil Pressure Sender

Black / White = Oil Pressure Sender

Red / Black = Starter Solenoid

*Tachometer connection is made @ back of Tachometer

**Separate relays should be used for the fuel pump and fans

 

 

 

 

The 9-pin connector (83-85)...

 

 

 

 

The 944 cooling fan circuit...

*A diagram for wiring the fan relay can be found here...Fan Schematic

 

 

 

 

 

And the 944 fuses and relays schematic...

 

 

 

 

* A high-res picture of the 944 DME wiring can be found here...DME

 

 

Armed with these, you should be ready to do battle with the LT1 wiring harness. An in-depth guide to harness modifications that includes GM pinouts can be found here...http://www.porschehybrids.com/gallery/album90

 

This guide is still under construction, so check back for updates.

 

 

 

 

 

 

 

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