QuestionQUESTION: Mike:
I purchased a 1998 Jeep Cherokee Classic with high miles. I also purchased a totaled 1999 Cerokee Sport with 44,200 miles on it. I am transferring all the parts off the 1999 to the 1998. I went to use the electrical harness off the 1998 on the 199 engine and manifold. The fuel injector plugs didn't fit so I put the 1999 harness in that hooks to the front 2 snap connections on the computer. The third connection on the computer is the one that the wires go inside the Jeep. I left that one in place. The pins were all the same on both front wiring harnesses. The only difference is the 1999 had a 3 wire switch going to the oil pressure regulator. The 1998 had a 2 wire switch. Which is fine because I have the 1999 engine and all it's components in the 1998. Do you think this setup will work? I'm afraid to hook the battery up, hit the key and fry the computer...
Thanks Mike
ANSWER: I assume that what you are referring to as the oil pressure regulator is in fact the oil pressure sender. Not all of the wires from the sender go to the computer(ECM), it is also responsible for feeding a signal to the light or gauge on the dash. So, hooking this up will not cause a problem. The only problem you might have is with the oil pressure gauge or light functioning correctly. If you look at the color codes on the old harness and the new one, some of the wires to the switch should match, and one won't. If the gauge doesn't work(or light, it should be on with the key on and the engine not running, off with it running), you might try using the switch out of the old engine and just connecting the wires with the same colors as in the old harness. But, so far as damaging the ECM, that is not a problem, it only uses the oil pressure signal to turn the engine off in event of an oil pressure failure. If you look at the color code at the switch and at the ECM, you will see that one of the wires from the switch goes to the computer, and the others don't. You should be using the 1999 ECM, by the way, although odds are that the 1998 one will also work.
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QUESTION: Great answer! Thanks
I will use the 1999 wiring harness for the motor and then try it on the 1998 computer first. If I have any issues I will switch to the 1999 computer and see where we end up...
Question: The 1998 Classic has the extra overhead compass and fuel mpg indicator where as the 1999 Sport does not. Does the computer control that? Or is there just 12 volts sent to it and it controls itself? I see quite a few wires in the plug that goes to it.
Thanks again!
Mike
Answer The mpg indicator is probably hooked to the computer, as the only reliable way to make those estimations is by having vacuum, throttle, engine speed and vehicle speed data. The logical way to get them is from the same place: the ECM. The compass is just running on 12V, and needs to be calibrated every now and then; the details are in the owner's manual. Of course, it would be possible to get a loose approximation of the mpg from the speedometer, and, depending on how much Chrysler was willing to spend, that may be how they did it. I believe that they use data from the computer, as you never saw such devices on cars until they started using electronic fuel injection, which requires that all of that data be present.
