i was having low voltage problems,so i put in a brand new alternator and battery.now my voltage jumps around.at idle with nothing on it registers at about 14 on the volt meter,when i turn the air and lights on,it drops to about 11-12 at idle.when i rev it jumps to 14,and the lights and everything get brighter and stronger.i am thinking it could be a ground problem,cause i started hesitating around 3800 rpm right about the same time my voltage was starting to go low. please help,this sucks,i just spent 160$ and got nowhere

 

On the small plug on the alternator....are both wires in good shape?? One should have 12v on it when the key is to ON. Does that happen??? Sorry I forgot which of the two. One of the wires goes to a switched 12v and the other to a relay in the CPU that triggers the idiot lights on or off depending on the output of the alternator. By the way....do the idiot lights come when the key is to ON and go out when the engine is running?

 

This alt was the factory replacement or and upgraded alt???

also was it a rebuilt or remanufactured alt?

 

no the idot lights never come on,they used to when the key was "on",and go off when started.i dont even think they are coming on when they are suposed to,cause i know im low on antifreeze,and when i put the alternator in,the buzzeer went off for a second and then didnt come back on.the alternator was new from pep boys,it was lke 160$ should i test the wires from the plug on the alternator?

 

and you had the battery disconnected when you hooked up the wires right?

 

no i didnt,i just had pep boys tell me to check the grounds,to run a volt meter between the block and the frame,i did,and im getting 4.5 volts,they said anything over 1 volt from the frame to block was to much. my idiot lights never come on,the brake/belt ones are the only ones that work

 

HUH? Volts between the fame and the block??? What crazy way are you hooking up your meter? 18 years of professionally working on car electrical systems and I have never heard of volts between the frame and the block.

Anyway, always make sure you disconnect the battery before working on the alt and its connections. Leaving the battery connected is the quickest way to blow out the diodes in the alt.

 

positive to the block,negative to the firewall

 

Positive of your meter??? to the block, and negitive of your meter to the firewall...

and your meter set on DC volts?

You wouldn't get anything! Someone is smoking something or I am not understanding what you are really doing.

 

probably was surposed to check the ohms between block and frame?

 

Yep, that's what you normally would do... that why I was so puzzled when he said he has 4 volts between the engine and frame

 

He means that the differences between checking voltage with the block as ground and the checking voltage with frame as ground shouldn't be more than 1 volt.

Right?

 

no stuck the positive end of the volt meter to the block,and stuck the other end to a ground spot on the drivers side,and i got a 4 volt reading,the guy at auto zone said that was a good way to test your ground. as for my problem,why wont my idiot lights ever come on,and could bad grounds be my low volt problem?

 

If you really have 4+ volts resting on the block, then you have a considerably bigger problem than the battery or alt or idiot lights.

You have something that can cause a considerable fire and other problems. This would need to be fixed ASAP before driving again.


But as far as your idiot lights not working:

If you have a S4: Either the alt is bad or wired wrong, or the CPU has failed or the idiot lights are bad.

If your have a S5, then its only the alt or the idiot lights panel that is bad or wired wrong.

 

i dont see how the alt could go bad,i took the one thats been on there for years and swapped on a new one in the same place.can i grab a cpu out of a junk yard s4?

 

Why waste your money replacing parts unless you know what is wrong?

Check the CPU before replacing it. If you unplug the Alt, and ground the run trigger lead. The lights should all come on.

And as far as a bad alt... if you hooked up the alt with the battery connected, you could have blown out the diodes in it.

 

what is the "run trigger lead",keep in mind im retarded,so what is it the main output?

 

No, there are three wires hooked up to an alt.

You have a Run/trigger lead that has 12 volts on it while the alt is turning, and ground when the alt is not running.

You have the main charge wire which goes to the battery and car's electrical system

and you have the reference lead, which measures voltage at a point in the car (usually at the ignition switch or EFI circuit/fuse).

On the S4 (86-88) the tigger/run lead is the white/Black. The reference lead is Black/white, and the main wire is the large gauge black wire.

That trigger (white/black wire) will run all the way to the CPU.

 

Maybe this will help:

 

ok thanks man,this sucks trying to figure these things out