morgaan

Hi forums,

To preface, I've done quite a bit of research on the FD alternator swap into the FC chassis. I've sourced a majority of the information I needed for the most part. The FD alternator is currently wired into my S4 FC3S in the following way:

• (B+) terminal 4 AWG direct to battery (+) terminal
• (R) (B/W) terminal taped off
• (L) (W/B) terminal direct to alternator (dash)
• (S) terminal 8 AWG direct to ???

I've gathered that the (S) terminal needs a fused 12v constant power. Archives said to splice it into the wiring for the EGI 30A fuse. My questions are:

1. Which wire should (S) be spliced into? (picture preferred)
2. Is there a better source of power for the (S) terminal?

Hopefully this is in the right section. Thanks!
m

DC5Daniel

iTrader: (10)

There is absolutely no need to have a large gauge wire for the S terminal. It is a sense wire, to sense the voltage at the battery. 16-18awg is more than enough.

You're overthinking this, any fused source near the battery is sufficient for sense. The closer to the battery the better. You could literally use an inline fuse and a ring terminal directly on the battery post if you wanted.

morgaan

Hmm I was following mostly the instructions in the thread below:

https://www.rx7club.com/2nd-generati...-731501/page2/

My main reason for overthinking was to not cause a fire or short.

Any thoughts on using a ring terminal on the 100A 12v constant MAIN fuse?

DC5Daniel

iTrader: (10)

You're confusing two separate details from that thread. No one states to use an 8awg wire for sense. The two mentions of an 8awg cable are for:
1. Connection from the battery to the fuse box supply.
2. If you do not upgrade the B+ feed from the alternator, you can "double up" a new wire with the stock cable.

In regards to your follow up question, if you're asking about the sense wire still, you can do that, but you need to fuse the sense line with something sensible like a 20A fuse. The fuse is to protect the wire. 100A is fusing for a heavy gauge wire (such as 6awg), not an 18awg.

Sense, by design, is a circuit which requires very little current. That is the point, to minimize I^2R loses across the conductor and accurately sense what voltage is at the battery. Therefore, you fuse the sense wire appropriately for the gauge wire you're using. That is why 8awg or a 100A to protect the sense line is both ridiculous and unnecessary; there is nearly no current being pulled on the circuit.

morgaan

Oh okay! My confusion must have been from the battery to the fuse box supply. There's a lot of information to process after looking through all the threads and I'd rather do it right the first time than hack everything up.

I went ahead and ended up using a 15A inline fuse direct to the battery using 16AWG.

That makes a lot more sense (if I got b*nned for this I wouldn't be surprised.) 16AWG w/ fuse direct to battery seems like the move. As for the 4AWG (B+) terminal, I routed the wire directly to the fuse box rear bolt for the 100A MAIN as per that thread. Someone said that it was supposed to in that thread and everyone just ignored and went direct to battery but I'll try that out first.