Chasing an electrical problem...
Asked by LunaNik Dec 13, 2015 at 06:10 PM about the 1997 Ford Probe GT
Question type: Maintenance & Repair
Driving home last night, I started having weird power fluctuations. First,
every time I had to slow down, the stereo cut out and the headlights and
instrument panel lights dimmed. It stopped the second the tach got above
2K. A few minutes later, she started bucking in time with the power
fluctuations, which got worse. Now the lights were going out completely.
After about a mile of this happening intermittently, she died and I coasted to
a stop at the side of the road. I checked and had no power at all. No
headlights, horn, dome light, etc. The motor turned over but wouldn't catch.
Fortunately, I have epic friends with a car trailer who got me home.
She has a brand new battery and alternator. One of the terminals was a bit
loose, but tightening it didn't help. I checked the fuses. There's some mild
corrosion on the smaller fuses under the hood, but the 100A looked fine.
The mass airflow hadn't been jogged loose and the plugs were fine as far as
I could see. She wasn't overheating at all (coolant level good, hose
attached, fans plugged in). And that's the extent of my car knowledge.
Could it be a relay? Bad wiring somewhere? Voltage regulator? Did I get a
bad alternator?
8 Answers
Possible since the new battery when low on charge, do you have a multi-meter, and can you get the car started again? You would check for DC volts at the battery terminal when it is running, the meter should show 14.2 to 14.5 volts if it is charging. The battery fully charged would show 12.4 to 12.7 volts without the engine running.
No, it turns over (endlessly...as long as I have the key turned) but won't start. When I open the door, the dome light and instrument panel lights come on very faintly, but there's not enough power to even close the window. (I had to tape plastic over it since there's going to be rain tonight.) Headlights, horn, etc. won't work.
There sounds like a bad connection, Where? good question. It sounds like it is at the alternator, the positive cable that tightens on the back, I assume that terminal is what you tighten before putting on the positive cable? For the engine to be able to turn over ok, but not start, and power to the interior being low, could explain the no start. Coil may not be getting enough juice. Needs 12V. I think also the ignition control module should be tested also. Look for loose connections at the alternator, inspect wiring running down to the starter, look for anything bad.
When I said "terminal," I meant the battery. One of the lugs was loose, but still attached when I lost power. Tightening it didn't help. I'll check for loose connections at the alternator, etc. I DL'd the wiring diagrams, so that should help me out. I'm new to this, but I'm not an idiot...lol. Thank you for your help so far! I'll be back with news. :-)
Reading your post again, the power fluctuating sounds like a bad ground wire. When the new battery was put in where the cables & terminals cleaned? Follow the ground wire from the battery and clean that connection. Look at those battery cables, make sure they are in good shape, sealed up nice, no bare wire exposed at the connections, and at the clamps at the battery. Corrosion can seep in and a cable still can look good.
That might be the issue. When I was putting the new battery in, I did notice bare wire near the connectors. It looked like the cable housing had sloughed off. It's probably a good idea to start by replacing those as well as the fuses in the engine box that are corroded. I have DL'd all the Probe's circuitry diagrams. From your answer, I'm now suspicious that other wires are probably in bad shape and need replacing. Also, since I'm physically unable to do it myself as it requires dropping the motor, I trusted a friend who works on his own vehicles to install my new alternator. Unfortunately, he caused more problems than he fixed. I already discovered three and there may be more. He neglected to reattach the coolant line, plug in the fans, and tighten down the radiator. Ugh. Sometimes trying to save money costs time instead. Now I'll have to check his wiring. I hope he didn't screw that up too. Thank you once again!
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