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1998 Civic pulsing lights and jumping speedometer

We have replaced the alternator to no avail. The speedometer is mostly off, but periodically surges, jumping erratically. The cruise control does not work. At night the lights visibly pulse brighter and dimmer. The heater fan also pulses faster and slower. When driving and holding the accelerator in one place on level ground, the car itself (engine) actually surges so the car momentarily goes faster. We have been told to look for a grounded wire and have checked out the wiring harness but have not located the trouble yet. Could it be under the dash, or would a ground causing this magnitude of trouble have to be within the engine?

Sorry I dont have an answer but just wanted to let you know that a friend of mine has the EXACT same problem with his 1997 civic. Must be kinda common on these. If we figure it out will let you know

Thank you! I see there was a similar post in 2007, but no solution was ever posted. With us, the check engine light came on and gave readings of bad o2 sensors, but we figured there was something else going on and that the sensors were probably fine. A friend has the year civic and had the same problem a year ago, which he says was fixed by replacing the wiring harness. Maybe it is that simple, although not cheap. Look forward to hearing anything you learn.

You stated the alternator has been replaced in an effort to fix this trouble and I assume that the regulator is built into the alternator so that isn’t a possible source of the trouble. If that is correct then the next thing you may want to check for is bad connection in the main power buss of the vehicle. Check the main wire coming from the battery and ties to the fuse panel under the hood. Look for signs of heat damage. The problem could also be with the ignition switch. Clean the ground connections between the battery and the chassis. Also inspect the main wire from the alternator to the battery and check for a bad connection there.

You can use a voltmeter to check for voltage drops across a connection while the trouble is occuring. A good connection will have no voltage across it.

Seems we may have fixed it. After repairing the wires that were exposed in the wiring harness, we found a string on honda-tech which advised to replace fuse 15 if it was blown. It was, and we did, and it is all working fine now. We had replaced the alternator, but I do not think we needed to do so… I think it was all caused by the exposed wires in the harness creating a short which blew the fuse, which stopped the odometer and speedometer and set off the check engine light. We are cautiously optimistic that we have resolved the issue.