Late-model engine swaps and their control systems are notorious for being complicated nightmares. Due to advanced electronics and the seemingly endless mazes of wiring, relays, fuses, and emissions components, figuring out an engine conversion can literally take days and even weeks. Once the swap is completed, if one critical wire is overlooked or misconnected the rig will never run at peak performance levels.
We stumbled around in the engine bay of our CJ-8 as we attempted to install a salvaged factory harness and ECM on the Jeep's 5.9L engine. The wiring and computer were scavenged from a '98 Jeep Grand Cherokee that was fitted with the Magnum V-8. To our chagrin, our harness was missing a number of critical plugs, wires, and relays. Also, cutting apart the wiring loom while trying to trace the wires with a factory manual was extremely time consuming, and not a heck of a lot of fun!
Not wanting to spend months on wiring the Scrambler, we took the easy way out by calling Chris Squire, owner of Hotwire Auto. He builds complete "hot rod harnesses" (wiring harness control systems) for late-model engine conversions. About a week after sending him the pieces of our factory wiring harness and ECM (computer), we received a new one that looked better than factory. Every wire and plug was labeled exactly were it should be connected. Wiring up an engine swap doesn't get much easier than this!
 1. The Hot Rod Engine Harness...  1. The Hot Rod Engine Harness literally saved us from weeks of complicated and detailed work. The harness is complete and designed for plug-and-play performance. The control system includes wiring to the ECM, fuel injection plugs, transmission plugs, speed sensor, emissions connections to the upstream and downstream O2 sensor plugs, computer connections, and every other port and piece we needed. |  2. Tracing wires from the...  2. Tracing wires from the ECM plugs to their connection destinations on a junkyard harness can be a major pain. The whole loom may need to be cut apart, the wires sorted and unnecessary ones removed, and then wrapped back together to route properly around the engine and transmission. A number of self-contained engine/transmission control systems are available from Hotwire, and included in the bunch are the GM LT, LS, and Vortec engines and the Dodge Magnum, Hemi, and Viper engines-all are available with many automatic and manual transmission combinations. |  3. Our ECM was scanned to...  3. Our ECM was scanned to make sure it didn't have a security system that would lock it up. We also received the VIN and the factory build sheet for the Grand Cherokee that once sat behind this computer (this is important info to have if your engine swap needs to pass a DMV referee). For safety we mounted our ECM on rubber bumpers (rubber stoppers from the local hardware store) to take some of the shock out of harsh driving. Hotwire also provides new computers and can program used ECMs. |
 4. The salvaged harness was...  4. The salvaged harness was missing the left plug on the computer and also the transmission, speed sensor, and O2 sensors, not to mention a number of other vital components. We could have tried splicing those connections in, but it would have taken weeks and we would have had to salvage more plug connections since Mopar doesn't sell them. |  5. The new harness came with...  5. The new harness came with the OBD II-(ALDL) connector, which allowed us to use a scan tool to figure out trouble codes and any engine and performance problems. Every plug and wire on the harness is new so there's no need to worry about chaffed or worn-out old wiring and busted or missing connectors. |  6. Once the harnesses is routed...  6. Once the harnesses is routed and mounted in the engine compartment, two Optima YellowTop batteries will power the entire system. The batteries, sealed with spiral cell technology, are spill-proof and maintenance-free, so we mounted them up and out of the way with an Off Road Evolution dual battery holder. Keep your eyes peeled for more on this Hotwire harness in future installments of the Scratch-Built Scrambler buildup. |