Alternator dosnt charge battery
 

Im running a parallel install of ms2, the car runs fine just it will die once the battery is depleted. The battery light is on and also my tach isnt working if that has any correlation. I'm thinking that i might have a wire ran wrong but i never touched the alternator or tach wires going into the stock ecu.

99 1.8l miata with ms2

How is the parallel hooked up?
I'm not sure if the Stock ECU want to see rpm before it starts to control the alternator. How you should share the sensors (cam and/or crank) can probably be found (scattered) in more than 100+ places on this forum.
http://www.google.se/search?q=share+...miataturbo.net
A lot of reading but there are Brains on here that can guide you (quickly) much better than I can (a lazy slob that went with DIYPNP :p).

Currently i have it wired up like this sharing cam, crank, and ait sensors with stock ecu.
'99 OEM Connector Megasquirt DB37

3Y and 3W Injectors 1&3 DB34&35

3Z and 3X Injectors 2&4 DB33&32

3Q VICS DB4 (spr2)

3O IAC DB30

3M IAC12v to 12V

3P Fuel Pump (w/ immobilizer)

3N Fuel Pump (wo/ immobilizer) DB37

3I Clutch switch

3J Rear O2

3G IGN 1, 4 DB36

3H IGN 2, 3 DB31

3E TPS DB22

3F Sensor Gnd to MS GND

3A Gnd DB19,18,&17

3B Gnd DB7,8,& 9

3C Gnd

2K Tacho DB5 (spr3)

2I TPS Vref DB26

2J Crank DB24

2H Cam DB25

2F Knock

2E CLT DB21

2C Front O2 DB23 (not connected to stock harness, will go to wideband)

2B IAT DB20

1V Neutral

1Q Alt Warning light DB6 (spr4) "Still connected to stock ecu"

1O Alt Field DB27 "Still connected to stock ecu"

1R Cooling Fan DB3 (spr1)

1I AC Fan

1B 12v DC DB28

EBC DB29 (not connected to stock harness, will go to EBC)

Can you connect through the OBD port and check if the stock ECU is seeing any RPMs?

Why is your alternator field wire hooked up to the MegaSquirt?

Mine wouldn't share nicely. I'd expect that you need to remove the pullup from one ECU or the other, and probably need to diode isolate the inputs in order to successfully share tach signal inputs. I put a trigger wheel on the crank instead, because I had one laying around. In retrospect, I think that it was the harder solution...

ok minus the alternator wiring from the above wiring configuration. the alt feild wire is still going to the stock ecu.

Well i figured out why the alternator wasnt charging, the Ait wire coupler wasnt as secure as i thought it was. But now that the alternator is working the car bucks and miss fires alot at low rpm/throttle position. anyone know what could be causing that?

You need to tune the MS.