Fellow Members,
Good Morning. I am new to this forum and new to owning a Volvo. I purchased a 1992 Volvo 740 wagon as a daily driver but it hasn't worked out. On my first day of driving to work, all the lights on the dash would occasionally come on and then turn off. The speedometer and odometer would stop working as well. About All of the sudden the car died while driving. I tried to start it up but nothing, no sound, no clicking, nothing. I swapped the battery and the car started right up. I drove to Autozone and they said the alternator was bad, so I ordered and installed a new alternator. Drove it one full day with no problems. The second day the previous problems reappeared. I stopped at a gas station and the car wouldn't start back up. I left the car there all day while working and when I arrived to have it towed it started back up. I drove it home with no problems. I have been told that it is the voltage regulator causing this problem, is this diagnosis correct? If so, where is this part located on the car? I can't find any diagrams anywhere and there are several voltage regulators (completely different) showing up online so I have no clue which one is correct. Thanks!

 

The voltage regulator is a part of the alternator and should be new if you replaced the alternator. Prior to starting the car, when the key is turned to the II position does the battery light come on the dash? If it doesn't then check the bulb and make sure this is working. If not then the alternator - new or not - will not charge the battery.

I generally avoid shops like Autozone when buying parts for these older Volvos. I prefer to use online sites that specialize in Volvo like FCPEuro, IPDUSA, EEuroParts. These sites even offer genuine Volvo branded parts.

 

act1292,
I will check the battery light and the bulb this evening. Thank you for the tip on the online sites that specialize in Volvo parts.

 

I'd also be suspicious of the ignition switch. If it fails again before you try swapping in another alternator, try wiggling the key. I'd also have the current alternator bench tested before throwing in a replacement to see if the regulator is good or not and I'd keep a volt meter in the car to do some additional tests. The regulator's job is to convert the alternator's AC output to DC and to keep your system voltage under ~14.5V and to avoid over charging the battery which it does so by effectively opening up the charging circuit. If the regulator gets stuck open, your system voltage will drop to 12V (ie battery's voltage) and you will begin to drain the battery. Hopefully your battery light will come on to tell you when this happens. That said, if you have a switch issue, relay issue or wiring issue, you will see circuit paths drop to zero volts - ie your dash lights may go off, the starter may not engage etc.