1998 Grand Marquis electronics require "reboot"

I was sitting in the back seat of my Dad’s 1998 Grand Marquis last night on the way back from a fishing trip yesterday. We had the family boat “in tow” and were doing about 60 down the highway when the windshield wipers started wiping all by themselves, the headlights started flashing on and off and the dash lights started blinking and the car seemed to stop and start at intervals. My dad quickly pulled the car over to the shoulder, turned it off and put on the hazard lights so we didn’t get rear ended by a truck. I jumped out and checked to see if the hazards were flashing (they were) and I asked my dad to pop the trunk so I could reseat the trailer light connection. After about a minute, he started the car and everything seemed to work fine and we continued on the way back home.

After about 10 minutes, it happened again. Again we pulled over and put on the hazards. In about 10 seconds, he restarted the car and on we went.

As we got close to my home, the same thing happened at an intersection in town. I think I noticed that he needed to turn the key all the way off and then then wait a few seconds before trying to restart the car…as if the electronics needed to “calm down” for a second before “rebooting”. I’m a computer nerd, so I was thinking that this must be related to the computer in the car somehow, and not just a general electrical issue, which I would guess wouldn’t respond consistently to this “stop and start” treatment.

He dropped me off and drove home, needing to stop and start the car 6 more times before he made it.

Anyone have this experience before?

The first thing to have checked is the battery and charging system. If the voltage to the computers/modules drops too far, these computers/modules will begin to shut down.


You said that you had to reset the trailer wiring—check that out too, since it’s not ‘normal’ equipment on that car. Perhaps you have an intermittent short to ground or another wire that is causing the body controller module to ‘freak out’ Other than that and the suggestion Tester had to make sure the battery/charging system are in good order, I’d say you may have an intermittent loose connection/bad ground somewhere (possibly the ignition switch?) or the BCM may be going bad.

I don’t think the ECU is bad but it does sound like there is a intermittent connection problem in the main accessory power buss or possibly the ignition switch. The wipers and headlights have control modules and it sounds to me that power is getting interupted to those areas and the other things you mentioned. You may be able to pin the area down by tapping on suspected trouble areas with a screwdriver handle.

This is typical of what happens when a diode (rectifier) in the alternator goes bad and allows a major A/C ripple into the electrical system. Have the alternators output checked by a shop with proper diagnostic tools. The A/C component can make everything in the car go nuts…

Usually, with radio set to “AM”, you can hear the loud A/C buzz that will vary with engine speed…

Do some reasearch and find out what a PC and a cars computer have in common.

There are so many things that could be going wrong. First let me say that turning the vehicle off does not reboot or reset. The power must be removed from the PCM to do that. Either remove the negative battery terminal or pull the PCM fuse.

As Cougar indicated, this car does not have a BCM. It does have an LCM (lighting control module). That controls all the lights you are having problems with. You put this at great risk if you just tapped into the wiring to install the trailer connection. You need an isolator. A new one will cost you 4-6 c-notes. The wipers have their own control module. (There is also a driver door module, DDM and an air suspension/power steering control module.)

Cougar and Caddyman have some good advice. I would also check out the main power feeds. You could try sniffing around the battery junction box because you might have had some arcing in there. If you need a wiring diagram in a hurry, www.alldatadiy.com is good.