GM Harness & PCM Services

Reference: GM Gen III / IV harness layout and PCM compatibility guidance.

One of the most significant things an installer can do to speed the conversion process along and keep the headaches at bay is to have a clean, well-planned wiring solution. Novak has supported GM Gen III / Gen IV Jeep conversions for decades with conversion-focused components, guidance, and programming.

Wiring Harness Overview (Reference)

Typically, the conversion installer will get the factory engine harness from the donor vehicle. This will include every wire and connector between the PCM and the engine's sensors (Oxygen, Throttle Position, Crank Position, etc.) and the active systems (coil triggers, injectors, IAC, etc.).

For current harness solutions, see the GM standalone harness options in our electronics catalog.

Vehicle Speed Sensor

This sensor will allow you to run a conventional cable drive speedometer and send critical speed data to your GM PCM for proper powertrain operation.

Harness Mods (Legacy Reference)

The following list is retained as a reference for what a conversion-focused harness typically addresses. (This does not indicate current availability of a harness modification service.)

• Install DLC port for installation in the Jeep cab
• Provide fuel pump relay and simplified fuel pump circuit
• Provide a simplified and water-tight power distribution center with standard ATC-style fuses and relays
• Simplify main 12V and main ground circuits
• Front & rear O2 sensors will be retained. Rear O2 sensors may be programmed out if requested by the customer and permitted by your jurisdiction
• Provide an easy-to-install MIL lamp
• Provide VSS leads
• Fully inspect all circuits
• Install a standalone air conditioning control circuit
• Provision for standard shift or automatic shift (typ. 4L60E or 4L80E) transmissions
• Minorly damaged harnesses can be repaired. For more extensive damage, reasonable additional costs will be determined
• Five wire hookup (manual trans option) or seven wire hookup (automatic trans option)
• Park / Neutral safety switch will be added for Jeeps that originally did not have this circuit
• All trunks and branches are arranged and wrapped with new split-loom and made to more appropriate, standardized length for Jeep vehicles.
• A tachometer signal wire, required on many aftermarket tachometer solutions.
• If you are wishing to keep your 1996-2006 XJ / TJ factory tachometer, consider Novak's tachometer emulator module, as seen here.

Pictured left is the extra heavy-duty relay used in many conversion wiring solutions for radiator fan control.

Identifying your GM PCM

GM Generation 3+ PCM's come in three major styles as follows:

The early Generation III PCM, 1997 to 1998

The late Generation III PCM, 1999 to mid-2007

The Generation IV PCM w/transmission controller, 2005-2020

Make sure your PCM and harness are compatible if they were not pulled from the same vehicle. Intermixing PCMs and harnesses can yield unexpected results. Always consult us on this before moving forward.

Note: If time is of the essence, contact us directly for current lead times on currently offered electronics services and products.

Disclaimer: Any modifications to a harness after it leaves Novak, without express written permission, may void warranty coverage on any Novak-provided harness product. This includes cutting wires, modifying lengths, or changing connectors. If circuits are unused (emissions, evap, etc.), leave them intact and secure them.

Shipping Instructions (Legacy Reference)

Need a cool way to attach your PCM to your Jeep? Our PCM mounting bracket assembly solves problems of placing and mounting your PCM in your engine bay.

Please see our Contact page, where you'll find our physical address and contact options. When shipping electronics, we recommend you insure your items appropriately for replacement value.

Please do not send anything other than what our sales team requests. If you are not sure what is required for your situation, contact us before shipping.

The harness provided must match the intake and throttle body being used. This will eliminate the possibility of incorrect sensor use, harness layout and PCM programming issues. We do not need your Throttle Actuator Control (TAC) module if you have one (early Drive by Wire harnesses only), nor your accelerator pedal or its harness.

For inquiries and orders, contact our sales team at the number listed on the Contact page. Accurate lead times will be provided upon inquiry.