86 rx7 alternator not charging battery
 

hello there fellow rx7 owners. i bought my rx7 a few months ago. the voltage meter only read 12volts when i was driving. it would feel like the car lagged when i floored it until i got to 3rd gear and it really started to go. then sometimes would drop down to 8 all my lights would go dim and almost cut off. id give it gas a bit till it was at 12volts again. this was happening for the first 2 weeks.i checked the ground wires and they seemed to be in good shape. i checked the alternator and it looked like the B positive wire was burned/not connected at all. i replaced the wire and i had way better throttle response. i had power in every gear and it didnt feel like it was lagging. but the voltage stayed at a constant 12 for about a few weeks. then the voltage would start dropping again. but this time wont go back up. and it completly killed my battery a few times while i was driving. so then i replaced the battery and the alternator to see if that would fix my problem. but it didnt. i took the old and new alternator to get tested (multiple times) and they both passed every time. i took it to my buddy because he knows more about wiring than i do. he told me he bypassed the alternator (idk exactly what he did) and it was working and running at 14volts but wouldnt shut off unless you disconnect a wire. so he made a switch for it, turned the car back on and it wasnt working again. disconnected the switch and put it back to the way it was before and it wont work again. we checked all the fuses and they were good. i just dont know what esle to do and i would appreciate any help that you guys could give. thanks

a couple things to check.
Bad alternator
bad battery
corroded wiring( the car is 27 years old,deal with it)
loose or slipping alternator belt.

Bad judgement of letting your "buddy" work on your car.
(rules #1 and #2 are don't let your buddy Drive OR work on YOUR car.)

Well the battery and alternator Are new. I got the alternator tested like 5 times and it passed every time. So I'll tighten the belt a bit and double check the wires and see what happens. Rhanks

It's best to check the voltage of the alternator via the output wire rather than the gauge for the gauge might not be accurate and the output wire (B+ wire) should always give you an accurate reading.

If the alternator acts normally after reving the car then the alternator is not exciting itself at lower rpm's.

There are two wires in a plug that goes to the back of the alternator. Are they plugged in. Black/White wire is on top of the White/Black wire. W/key to on, both wires should have 12 volts when unplugged from the alternator. W/the plug connected and key to on the B/W has 12 volts but the W/B has close to 2 volts or so. If the idiot lights turn on w/key to on then the W/B wire should have the proper low voltage.

When you got the replacement alternator did you get an S4 or S5?

A new alternator from an auto parts store can be poor even though it might test out okay.

The charging ground wire comes off the battery and runs to the driver fender well where it is mated to the body. It then runs down to the long starter mounting bolt. Both points should be in clean and proper shape.

Hmmm ok I take a look at that and see what I get. I got an s4 alternator from O'Riley's auto parts

If you are still having trouble, there is a connector in the positive wire coming from the alternator to the main fuse block. If this connector is flaky or corroded, the alternator output cannot get to the battery. I can provide details on the location in the morning if you want to check it out.

I had a similar problem and it was the fuse on B+ wire between battery and alt.

Yes pleas that would be much appreciated

I tried that but it didn't work :/

Here you go. This is my '88 vert. Yours should look the same...if still original wiring. Good luck.

https://www.rx7club.com/members/robb...ctor-55984.jpg
https://www.rx7club.com/members/robb...zoom-55985.jpg