Having sporadic electrical problems with our car. A couple of months ago I was driving home on the freeway and noticed that when I engaged the brakes my headlights would dim slightly. This happened for a few miles and then stopped. I had actually forgotten about it because it never happened again. A week ago my wife was driving home and all the dash lights started coming on and off. The radio stopped working and the speedometer was going crazy (up and down). She said the car drove fine during all this. When she got home the car wouldn't start. It seemed liked a dead battery. I tried to start it a couple of times and on the 3rd try it started and ran perfectly fine. We took the car and had the battery and alternator checked and both are fine. This morning the car wouldn't start again. Again, it appeared to be a dead battery. I tried starting it a few times and nothing. I started playing with the driver power seat and after a few clicks the seat was moving. I then started the car with no problems. As it was running the interior and headlights would dim if I hit the brakes. I've checked the battery terminals, cables, and grounds and all appear fine.

Any suggestions?

 

You have covered the usually causes.

A few thoughts.

By narrowing down the common electrical circuits for the components that don't work you may be able narrow down the problem area.

The starter motor receives power directly from the battery via a large cable going to the starter solenoid attached to the stater motor.

The solenoid is engaged by the ign key switch that activates a starter relay supplying 12V to the starter solenoid coil. This power comes from the battery through a fusible link, the splits. Power to the starter relay contacts goes through the AM2 fuse and ign switch.

Power to energize the starter relay solenoid goes the AM1 fuse, ign switch (its a double pole switch), then through the park/neutral or clutch switch.

If the starter is not working, power is not getting from the battery through the starter solenoid contacts (inside the starter solenoid) to the motor or not reaching the starter solenoid coil via the starter relay circuit.

Power seat electricity comes via the power seat fuse, then a 120A fuse, then a main fusible link to the battery. There are no relays, switches (other then those at the seat) etc between the seat and the battery.

If the seat is not working something is wrong between it and the battery.

Issues of head light dimming, speedo jumping, no radio, etc can be signs of low voltage.

The brake lights are placing a load on the system that the battery or alt cannot compensate for and the result is the headlights dim. If the engine RPM is over 2000 the alt should be producing enough power to handle all electrical loads.

Or there is some kind of poor electrical contact causing a momentary reduction in power.

The starter and seat issues occur when the engine is off. You stated the items can start to work normally which excludes alternator problems as it is now off.

When the starter and seat do work you appear to state they work normally, no reduction in operation due to lower voltage or available current. This would indicate the battery is OK.

These leaves the wiring, fuses and possibly the ign switch as it operates the stater relay but this would not explain the seat issues.

When the engine will not turn over, if you have a volt meter find the SMALL wire going to the starter solenoid (Black/Red). Determine if 12V power is available at this wire when the ign key is turned to start. The starter solenoid also has the large red wire coming from the battery, you don't want this wire.

If no power the issue is the ign switch or again the wiring,fuses, battery ground, etc. Since the power seat also has problems I will eliminate the ign switch as it has nothing to do with the power seat.

The common sources for power to the starter and seat are the battery, fusible link and 120A fuse.

Suggest checking the following:

Battery ground cable were it attaches to the cars frame/chassis.

Battery terminals where they attach to their cable.

120A fuse (located in box, left side of engine compartment).

Fusible link. Not sure exactly where this is. Most likely a small plastic box mounted on the frame, engine compartment between the battery and fuse box holding the 120A fuse. Inside is a section of metal that burns through if overheated. Sometimes the metal can start to fail due to corrosion, making intermediate contact. It might look OK, but have cracks, etc.

 

Thanks for the reply!

My wife drove the car to and from school with no problems. After she got home I pulled the battery out again and re-checked the cables and grounds. I also checked the fuse box (both dash and under the hood). I couldn't find anything. I tried for an hour to recreate the issue but was unsuccessful. I think I may have mislead you by mentioning the power seat. We have never had any problems with the seat itself. When the car was dead I was just using the seat to confirm. After pushing the button a few times everything started working. A couple of mornings ago when we had the same problem (car wouldn't start and appeared to have a dead battery) I never touched the seat controls and was able to start the car on the third try turning the key in the ignition. Each time this has happened the car is completly without power for a few seconds (clock resets, CD ejects from stereo, ect). My wife also told me that when she was driving home yesterday that the headlights got dim and then the radio went off (as if it did not have power). Again, she advised that the car drove normal while this was going on.

 

Don't know.

When this dead battery event happens the electrical system is completely dead. No headlights, dome or dash lights. The ign key is turned to ON and nothing lights up on the dash as if the battery was not installed in the car?

Of something happens when the ign key is on, the dash lights may be on but dim when the ign key is turned to start?