1990 Volvo 740 doesn't charge the battery unless jumpered f

ADAM CRO

MEMBER
1990 VOLVO 740
4 CYL
2WD
AUTOMATIC
190,000 MILES

I've changed the battery and alternator. Still the battery light on instrument panel is lit. On this type of Volvo with a charging problem 4 other lights also come on Brake Fail light, Parking Brake light, Bulb failure light and Low Washer fluid light. I read in the owners manual that this is normal for the other 4 lights to be on when the system isn't charging.

I believe that there is a relay or a fusible link or something inbetween the alternator and battery where there is a disconnect. When checking Ohms between battery (+) and alternator (+) it's an open circuit (whether the car is running or not). Right now I have the alternator jumpered directly to the battery with two 30 Amp fuses inbetween. The dash lights are off and it charges normally when the jumper is hooked up. If you remove it the 5 lights come on again and the car just runs down the brand new battery.

Where should I look to find the disconnect? Is it under the dash, or do I just have some fried wires somewhere.

1 Reply

2CARPRO JACK

MECHANIC
11,533 POSTS

I have included the wiring diagram for your Volvo, it looks like that charge wire goes from the alt to the starter then to the battery, so you may want to visually inspect it for any burnt or broken wires, or possibly a fusible link that my wiring diagram doesnt show.If necessary, you can replace the entire wire and it wont hurt anything, but you may want a little larger fuse than a 30 amp, that will blow quite easliy.