5.0 Alternator Wiring/Troubleshooting
 

Hi guys,
A few months ago I purchased a miata from a member on here who bought the miata already completed several years prior. I have been working on it quite a bit in my spare time and haven't had the opportunity to drive it much. Primarily because I am having an alternator issue. I thought the alternator was bad so I replaced that and I am still not getting any charging to the battery. I will admit, that I am a noobie, but I am wanting to learn. I read another thread on here about how the wiring has to go to the gauge cluster in order to tell the alternator to turn on. According to the thread, one way to check this problem is to see if you have the battery light illuminating when you turn the key on with the engine off. I do not have the light, so I think my wiring is incorrect. I'm not sure how to verify that though. Also, I read about the wires coming from the alternator and how they need to be spliced with the miata wiring. Can someone please post a picture of the wiring coming from their alternator? I noticed that on my alternator, the green wire had been cut. I have not read of anyone else cutting theirs. Any and all help on getting my alternator issue resolved would be greatly appreciated! Here are some pictures of what I have:

If that is a standard Ford type alternator, I don't think it could have ever worked with it wired up like that.

Do you know if the charging system has ever worked in the past? Currently it is connected up as a "one wire alternator". That connector with the yellow and white wires has the green wire cut off as you mentioned. It is that wire - the green one - that needs to be connected to a switched +12V source which typically has the charge light in the cluster in series with it. The Miata wire should be in the same loom that has the large high amp output wire (looks like there are two wires connected to the stud). On a side note, a lot of people do it the way yours has it regarding the yellow wire. It should really be routed all the way to the main relay/fuse box so that the alternator can monitor the voltage output where it is being "utilized" at instead of itself. This allows the alternator to compensate for voltage drop from the alternator output to the main relay/fuse box.

Thanks for the reply, Mike. The previous owner said that there was a "small battery drainage" due to the amp he had installed and that if he didn't run the car for a month or two, it would have a dead battery. Definitely not the case when I took it home, and obviously was not the case when he had it either. So in order to correct the problem, I need to buy a new connector and connect the yellow wire to the fuse box and the green wire needs to be connected to a switch 12v wire? How would you go about doing that?

It is not absolutely necessary for the yellow wire to connect at the fuse box but you will need to get the schematic for your year car to ensure you are finding the correct wire that will go to the Ford alternator Green wire connection. It will be a switched power type wire that comes from the dash gauge charge/alt/battery lamp indicator.

If you are going to connect the yellow wire to the main fuse/relay box, I would put it on the big lug that is there which is the main power to the box and is always hot if the battery is hooked up.

I have a questions along the same wiring issues with it. For my car the white/green wire is the wire going to the main/inj/and relay. That wire is putting out 12v when the car is on, However, the yellow/white wire coming form the voltage regulator appears to be grounded, or a direct short to ground. I checked the wires, they are good, the short itself is in the voltage regulator. Is this normal to be grounded out? I am not thinking so, I have already destroyed several batteries trying to figure it out.

Update: I just checked it. The white/green wire has 12 volts all the time, car on or off.

Miatafrog,

I sold my car in 2017. I looked through my photos and I don’t have any helpful photos for you of how mine was set up. I’m sure some of the guys on here or on the V8 Miatas fb page will be able to help you though.

This may not be helpful at all but here goes. Not knowing the year of the components, I searched for SN95 charging system. Mine was a SN95/95 Miata swap but it's long gone. On mine, it was easy-peasy as I recall. Anyway, here's a particular link in case it helps. Note that there could be a fusible link in there someplace.

https://www.stangnet.com/mustang-for...arging.792394/