i drive a 98 civic ex 2 door....just randomly the other day my electronics all but the audio started pullsating, even the spedometer stopped working (brand new speedo sensor), and the tacometer is screwy. i replaced the alternator and it is still having the problem. both alternators tested to be good. i've redone all the engine and electrical grounds, and checked all fuses and relays. but heres what gets me. if you unplug the alternator, and let the car run off the battery, everything is fine and normal. and it only does it when the alternator is hooked up and the engine is running. i've even tried a friends new battery. which the battery is also not getting a charge from the alternator. is this a common problem or does anyone have any other ideas of what might be wrong? thanks for all the help anyone can give to me!

 

Is the CEL ON (see link in my signature)?

First, carefully double check whether under-dash fuse 15 (7.5A) is blown or loose.

 

sounds like it could be a voltage regulator...but there are others on here who have far more experience with electrical.

 

Did they bench test the alternators? The bench test will determine whether the voltage regulator is functioning properly or not. The standard "in-car" test cannot determine much.

 

i've already checked all the 7.5a's and 15's. lol, and yeah i had the alternators bench tested. i've pretty much done tried everything, thats why i'm so stoked! i hate electrical! i don't know what else it could be

 

oh, and yeah, the cel comes on when it realizes that the speedometer isn't working.

 

if the alt is good, then it's obviously the connection from there to the rest of the electrical system. have you changed the connection from the alt to the rest of the car? consider downloading the factory service manual from the link in my signature and see what other possibilities. Since you have eliminated the alt as the cultprit, there are other connection issues.

 

Retrieve the CEL code(s) from the ECU (see link in my signature) and post them in your thread. There is a possibility that you have a short circuit problem common to 6th generation Civics:

http://autorepair.about.com/library/faqs/bl021d.htm

 

ok, i will work on retreiving the codes, and i'm downloading the repair manual now. thanks for all the help i'll post back soon

 

Yeah, first pursue the potential short circuit problem as you are doing. If that doesn't pan out, then do a continuity test on the wire (highlighted red in diagram) that runs between the fuse box and voltage regulator in the alternator: