Cosmo 13B-RE alternator wiring
 

Hi,

I have searched a lot these days to find the wiring diagram to wire up my 13B-RE cosmo alternator. My battery is draining and I think it could be caused by the alternator.

On the top plug I don't know which wire is the S terminal and which wire is the L terminal. My guess is it's the same thing as the FD alternator but I'm not sure cause my battery is draining itself. Can somebody validates my diagram in attachment?

Also I would like to know if it's correct to connect the S terminal directly to the B terminal or I have to connect it directly to the battery?

My car is a S4.

Thanks.

wires the same way as a FD alt.

If it is draining then you have the S and L backwards or have blown the internal diode.

https://www.rx7club.com/attachment.p...hmentid=146552

That 'S' terminal is the remote voltage sensing wire. If you connect it to the 'B' terminal, then your alt will maintain the voltage at the alternator terminal. Any voltage drop from the alternator through to the main fuse block will not be compensated for. Under low load conditions, this may work fine. BTW, this is the way a 'one wire' alternator works.

Under high load conditions-lights on, amps thumping, E-fan running A/C clutch interior fan running- the voltage drop might be as much as one to 2 volts from your 'B' terminal to the fuse block. In this situation, the alternator will not supply the desired voltage to the main fuse block, which is really what we care about, NOT the alternator voltage!

For example, when I test my bat voltage at 14.1 volts, the B terminal on the alternator is closer to 14.5 volts at idle with no accessories on, stock wiring harness. This is a voltage drop of .4 volts and is normal. Turn on my efan and A/C the drop becomes nearly 2 volts. If the S terminal was connected to the B terminal, at idle my bat voltage would be 13.7 volts and with the accessories running the volts would be 12.2 volts. I my opinion this is unacceptable and not the way Mazda intended the system to work.

Best solution is to run the 'S' terminal remote sensing wire to the original location on the main fuse block attaching to the EGI fuse(30 amp) . The 'B' terminal should attach to the Main fuse (100 amp).

This allows the alternator to raise the volts higher at the alternator to compensate for voltage drop in the circuit, thus maintaining the 14.1 volts at the fuse block.

If you MUST wire the 'S' terminal directly to the 'B' terminal, then you really need to upgrade the charging wire to a very oversize wire to attempt to reduce any voltage drop.


I hope this all makes sense.

Thanks a lot. That's make sense.

But is the cosmo connector physically the same than the FD connector? I mean is the S terminal located on the same side than the FD connector? Can someone confirm this, I don't have the connector diagram?

Excellent pictorial Icemark. If it isn't, that should be stickied or in the faq for alternator upgrades as MANY people do the S4-S5 or S6 and often end up with drained batteries. I ran into a similar prob a few days ago when installing my Motec harness and REALLY could've used that as opposed to running through the online FSM's

On the 13B-RE alternator connector there is a beige/blue wire and a beige/black wire. Somebody knows which one is the S terminal ?

The cosmo alt and the S6 alt are the same.

As a rule, the 'S' Terminal will be a larger gauge (thicker) wire than the 'S' Terminal.

ok i wired my cosmos alt and that didn't charge at all......... i even tried instead of the b term to battery i jumped it to the fuse box and nothing still......

i think i might have this prob :(

:scratch:

Or the alt itself has just shit the bed or is being way underdriven. Whats the voltage that it's putting out?

Wow great diagram.......... Thank's

Well when I removed the alternator yesterday I noticed that there is a sticker with a nice diagram on it that tells which wire is the terminal S and the terminal L.

The alternator shop are repairing my alt and they told me that the light circuit was blown. I hope that this will fix my problem.

pretty common if the two (S and L) were mixed up and wired backwards from what they should be.

If you are doing a full rewire, best thing to do with the L terminal is to wire a bulb in series, pulling 12v from a switched 12v source. In this diagram 1 is L and 2 is S. This diagram also includes a resistor in case the bulb blows out, your alternator will still get excite voltage.