Car Dies after turning on headlights

[TTDRIVER]

I have a 73 240z which dies out as soon as I turn on the headlights, This wasn't happening before but started happening after I changed my fuses in the center console. The car also has no power even after its been running.

The car has a new battery, alt. What gives?

Thanks,

Saro

[Nigel1943]

Are you getting full charge from your alternator?? Is the voltage control unit working??

[SteveJ]

Why did you have to change your fuses? Why do you think that could be a contributing factor?

Having asked those questions, it's time to do a proper diagnosis. Use a voltage meter to read the voltage at the battery with the car running. It should be somewhere around 14.5. (I don't have my FSM handy.)

Next, use the FSM or Haynes manual to diagnose the voltage regulator.

Let us know what you find out.

[wymdawg]

nice reply steve 14.5 volts is a bit high though i've seen cars less than 1 year old run as low as 12.8 volts running it depends on what is on a.c. lights etc. etc. definatly use a manual as guidlines for diagnosis (haynes , chiltons etc.) and a good idea of how electricity works helps as well.

[SteveJ]

As I get older, my memory grows weaker. The voltage should probably be closer to 14 volts at idle without the headlights on. I'll edit my post if I can remember to look up the numbers when I get home.

Also, Saro, don't forget to check the tension on your alternator belt. If it stretches, that can affect the alternator's ability to provide power.

[TTDRIVER]

Thanks for the advise. I added a few fuses which is why I assumed would be the cause of the problem. Im going to jump start it and disconnect the battery to see if the alt. will keep it running. If it dosen't stay on, then my new alt. is probably bad. I dont have a volt meter so If all else fails, I'm gong to have to take it to my mechanic.

Thanks,

Saro

[MikeW]

I dont have a volt meter so If all else fails, I'm gong to have to take it to my mechanic.

You can buy one for $10 or $15. A multimeter will measure voltage, resistance, and amperage - all of which can be quite useful working on these cars.

[SteveJ]

Thanks for the advise. I added a few fuses which is why I assumed would be the cause of the problem. Im going to jump start it and disconnect the battery to see if the alt. will keep it running. If it dosen't stay on, then my new alt. is probably bad. I dont have a volt meter so If all else fails, I'm gong to have to take it to my mechanic.

Thanks,

Saro

HOLD THE PHONE! You ADDED fuses? Fuses are devices designed to protect electrical devices on a circuit. So, did you add circuits and electrical devices, did you split existing circuits, or did you have some circuits that didn't have fuses in them? If you added electrical devices (new amplifier/stereo, car alarm, cappucino machine, etc.), you could be drawing more current than the stock alternator can supply.

As for a multimeter, Harbor Freight frequently has them on sale for $3.99. I picked up one to throw in my trunk.

Do you have a factory service manual or at least a Haynes manual? It is easy to check the alternator and the regulator without going to a mechanic as long as you follow the directions and have a multimeter. It took me all of 5 minutes to diagnose a bad voltage regulator in my Z. I'm not a big fan of "pulling off the battery cable while the car is running." It does not differentiate between a bad alternator and a mis-adjusted voltage regulator.

[Arne]

An interesting thought - does the car just die like there's too much drag, or die suddenly like the ignition was switched off? I'm not sure about a '73, but most early Z's activate the headlights by switching the ground, not switching the hot leads. If there is something shorted or misconnected in the column or fusebox area, turning on the headlights could ground out the feed to the coil. Something to consider...

[dogma420]

I also wouldn't recommend running without a battery...

[SteveJ]

Okay, so I have checked in the FSM. It says that the alternator is good if the voltage is 12.5 volts or more at 1100 RPM.

[TTDRIVER]

Thanks for the help guys,

SteveJ, By adding fuses I meant replacing fuses that weren't there, not adding more. Sorry for not being clear.

Arne,

When I turn on the headlights, it dies suddenly like the ignition is being switched off.

I drove the car the whole day, parked and started it many times with no problems. My last stop was to Pep Boys were I bought the fuses and replaced all before I left the parking lot. I started the car and drove all the way home with no problems until I parked the car and couldn't start it again. I roll started the car and let it idle to recharge the battery and that's when I discovered turning on the headlights causes the engine to die out. I tried a few times to turn on the headlights but kept turning them off quickly so that I could keep it running. After a few more attempts of this, I kept the lights off and the engine running. I tried to rev the engine and It completely died out with no power.

Sorry for the long write up, but the day all this happened was the first day I got it back on the road after two years.

I'm getting anxious.

Saro Fagerian