First let me say thanks for having this forum available to us frustrated old Volvo owners. I have a 1988 240 DL 4cyl gas with about 200k on it. It runs great and has been a good car for my 16 year old daughter. I have no output from the alternator. I just put in the second new alt. in the past two days, and after it did not work again I pulled it and brought it back to the parts store, they put it on their tester and it works fine. I have checked for a good ground at the green wire that goes on the back of the alt.to the block I checked for ground from engine block to battery. I have checked and actually ran a new red wire from the box on the firewall to the back of the alt. This wire has 12v on it with the key on car not running when it is disconnected from the back of the alt. as soon as you hook it up to the spade on the back of alt. the voltage drops to 1.8 volts. when the car is not running. After you start the car this small red wire shows 12v. I have checked for alt. output directly on the main terminal with car running and I just get 12v I have tried a new battery and a few other things but I am totally perplexed how can it work on the bench but not in the car. I have checked previous threads and I that is where I learned to check the things so far. Any help would be greatly appreciated. Thanks Mike

 

This is OK .... on my car it's 1.6VDC. Some of my past posts probably weren't very clear on this so I'll change that in the future. Most of the voltage is being dropped across the battery light in the dash. With a test light you would "see" battery voltage with the small red wire connected but measure less than 2 volts with a volt meter.

But the alternator will start to produce ~12v when running ... 12v on both sides of the dash light, the dash light goes out.

So with the car running what do you measure from the big red post on the alternator to the alternator case?
What do you measure on the battery posts while running, while not running?

 

I read your post twice before I posted All your readings seem correct,now connect your original wire back to the spade terminal.Connect your volt meter to the battery,start the car,if it still reads 12v rev the engine a couple of times to about 2500 rpm.Volt meter should read 13.5v to 14v,if it doesn't alternator is bad.

The red wire from your charge indicator light excites the alternator when you start the car.You can actually unhook this wire(engine not running key off) and rev up the engine and the alternator will self excite.

I forgot to ask this,is your charge indicator light working? If your bulb is burned out alternator will not self excite.

Dan

 

Sorry it has been a couple of days to get back to you guys. Thanks for the advise. Yes I double checked the light in the dash and the voltage at the little red wire and everything checked out except still no output from alt. However I happened to notice that when revving the engine to check for alt. output it seemed like the alt. and power steering pump were not actually spinning any faster! So I stopped the car ,pulled the cap off the distributer and turned the engine over by hand with the belts. I can clearly see the crankshaft pulley turning but the rotor did not move . So, what is happening is at idle the pulleys all turn but at anything over a idle they do not go any faster thus no charge from alt. Apparently there is a rubber bushing in this harmonic balancer/crankshaft pulley that has gone bad. Has anyone ever seen such a thing? I am sure I could have ended up junking out this car out of frustration if I would not have figured this out. I have now ordered a new harmonic balancer/crankshaft pulley and will let you all now when it is done . Thanks very much, Mike

 

I have the same problem with a 1993 vovlo. After some doing I found that the ground did in fact need to be replaced. I have this car for as a second as it failed inspection,mostly electrical. I will in time get it back on the road,my first on the list to fix is. The head lights only come on when I press the brake and the high beems don't stay on , I am on the incompetent side when it comes to electrical but I can follow instructions good any one help me out?