91n/a...what is the normal operating voltage with no headlights on or any accessories...my alternator won't put out more than 13.9 volts at idle and when headlights are put on it goes down to 13.4 volts...is this normal??

 

Just about normal.
I'd check the primary & ground wires with a voltmeter.

Voltage test points: engine running, headlights & heater fan on high:
Alternator post to alternator frame = 13.5-14 (verifies the alternator output)
alternator post to battery + near 0 volts (verifyies the primay + wire)
alternator frame to battery - near 0 volts (verifys the primary ground)

 

thats normal

 

thanks guys...ill check those locations

 

No, normal is 14.4 volts with the engine running at idle and no load (Air condition is not on, headlights not on, brake not on etc)...

Anything under 13.6 and your not really charging the battery. You need at least a volt extra to charge the battery while the car is running.

 

Yep, too low. Go get your alternator checked out.

 

I think that's 12.6 volts...anything over 12.6 charges the battery, right?

 

No the battery is 12.6 volts, You need at least a volt + (1V+) for the chemical reaction to occur and to charge any battery above 6 volts.

 

Ice to the rescue Thanks man!

 

so do you think my alternator might be bad??

 

i know that this may sound stupid but every GM car that i've owned all put out over 14v at idle... when i turn my headlights on and depress the brake, the lights in the IPC dim

 

i think thats what hes getting at

 

It could be a lot of things...the alternator could be a bit weak, the belt could need a bit more tension etc...

Honestly, I wouldn't worry with 13.9 @ idle...what are you using to measure voltage? What is the voltage at the alternator vs. the voltage at the battery?

 

my 1st gen puts out 14.6volts, don't know about the turbo 2 with a volatage gauge?? whats your measure just off idle (1500) rpms? maybe this reading could help trouble shoot some way?
sorry to threadjack....my friends 87 base had a new alternator and battery installed in the car before he bought it, the battery cables themselves don't look bad but i'm not sure...anyways the main charging wire coming off the top driver's side of the alternator was a little messed up and was grounding out on the engine hoist bracket so we wrapped it with electrical tape but it keeps melting off. Also his charge goes down sometimes then might be normal and it varies alot, anyways what is the name of that cable off the side off the alternator? where does the other end go? we were going to replace the battery cables, but they go to the starter not the alternator. thanks for any help, sorry for TJ'n.

 

That should be the same for all cars with a 12V electrical systems.

 

The alternator cable goes to the fuse box in the engine bay. It feeds the MAIN FUSE. Remove the negative battery cable first. Then remove the mount screws on the fuse box and lift it up. You'll see where it is attached. That same wire branches off prior to the fuse box and feeds the ignition switch.


For the guy who has problems when he steps on the brakes......you might consider that switch on the pedal has been abused over ten years and MIGHT be getting a bit dodgey. R square that puppy. Then again it could be another thing altogether.

 

is there a resistance check for that switch or anything??