S4 to S5 alternator swap question (searched)
 

So I'm going to be putting an S5 alternator on my 88 vert and I was looking around to try to find the plug to switch onto my factory wiring. Because I know from the diagram the S4 alternator plug is different from the S5. Other than that, is that the only thing I have to change? From what I'm getting at from the Archives is it's just that plug. Thanks ahead of time for any help.

You will have to change the plug, and you will probably want to change the positive terminal post to the S4 one so it fits your wiring.

You can buy the plug supplied online, but I did that and it sucks hard core. Try to find a used plug the for sale section because it will be better. I ended up sourcing one from a friends old wiring harness instead of using the one I bought.

^ This is the way to go. For my FD alternator, I swapped on the old S4 B-post and spliced in a used S5 plug for the L & S terminals. There's also an empty slot in the fuse box where you can easily add a 30A fuse for your constant 12V source. Pull the plug from underneath the box, and press a wire w/ female spade connector into the open spot. Then run this wire up to the S terminal. Cut the old wire for the R terminal and tape it off. Reconnect the L terminal wire (dash) to your new plug, and you're done.

Be advised you want a Battery voltage source, not necessarily "constant 12v". It electrically (other than fuzes or breakers) must be connected directly to the battery positive terminal, no relays no upstream loads etc...

Yeah...such as the fuse box, which I mentioned already. This is exactly where power for the alternator comes from on an S5.

Why is this? I connected mine to a switched 12V source...

So can I just take my factory (S4) wires and put them onto the new (S5) Alternator? I have a couple other (S4) alternators in my shed that are bad if I need to ninja parts. I would idealy like to use the factory wiring and just pop those wires into the S5 plug.

Why even waste your time with an S5 alt? the plug is the same as the FD alt, and it would actually be a significant improvement. There were a bunch of threads about the FD/S5 alt swap and how to wire it so that it didn't drain the battery w/ the key off.

No, you will need to use a S5 plug and either swap the s4 terminal post onto the new alt or put a bigger ring terminal on the s4 wires. You will also need to run a 12V+ wire to the new plug and wire one of the S4 alt wires into the S5 plug.

I just explained exactly what you need to do, and there is a diagram in the FAQ. If you just stick the 2 existing wires into an S5 plug, you'll end up with switched 12V power on the regulator. This will drain the battery. You need a constant source, which means running a new, fused wire to the battery/fuse box.

If you use the car routinely then you probably don't notice the battery drain but if you left your car unattended for a period of time you likely would, so do as RR88 states.

^ Actually I have a fun story related to that. The 30A fuse I had in-line for my FD alternator's regulator got popped while changing the pulley on the car. Apparently spinning the shaft backwards a little with an impact gun was enough to pop the fuse; I'll be disconnecting the wiring from now on. It did create a slow battery drain, but the other thing it did was make the alternator get REALLY hot. I could barely touch it with gloves on. Improperly wiring the regulator with a switched 12V source will do the same thing if the engine is off.

So couldn't you just wire the 12V source needed on the plug to the B terminal?

I believe you would bypass the safety net that the 30 amp fuse provides.

Yeah, you could run a short wire up to the B-post, but you should still use an in-line fuse as satch mentioned. A fuse holder could be wedged in that area if you wanted to.

On my race car we connected it to a 12v that was downstream of a relay. The voltage would rise with RPMs up into the 15s. Once we changed it so it was directly on the battery circuit it held steady at 14.3-14.6

The voltage regulator uses the voltage it sees on the battery feed to regulate the voltage output. It is quite sensitive.

I could see that downstream of the relay you may have some loss in voltage. What would cause the alternator to drain the battery though if its not 12V constant?

I tried searching for the old threads but can't find them very quickly and work has been hectic recently.

And it sounds like I will be rewiring my 12V line when I get some time.

Okay so someone said there is an empty space somewhere on the fuse box? Inside or under the hood?

Engine fuse box.

Sweet. And that doesn't get power until the ignition is on?

I think you may be doing this on purpose but the answer is NO! You need constant voltage and that is why you choose the engine fuse box because it always supplies constant voltage.

http://img808.imageshack.us/img808/4...rwiring.th.png

I already have the S5 Alternator

Sometimes I drive it, sometimes I don't.

Awesome thanks man!

Alright I'm running 12.5 volts right now with my S4 alternator, and it runs really choppy until I get higher rpm's. I think one of my coil-packs isn't getting enough juice or something along those lines. Doing it the swap now! Will post pics.

Okay so the first pic is my old alternator. I didn't paint that I just want to be clear. It's running 12v to 13 volts depending on the rpms...

Second Pic is the 30 amp fuseable link I installed, then plugged a wire into the bottem of that for my constant? You will see in the 3rd pic where I plugged it into. And the other plug is the White/black (not Black/white) wire. K then I took the B terminal off a scrap alternator I have and mounted it onto the new alternator. If I remember right, it says on the alternator which plug is which. But I didn't double check, I went off the pic (which wasn't exactly the same btw). I took the wire I had plugged into the fusebox w/ the fuseable link, and toutched it to a little led I have for a test light and grounded it and nothing happend. So I'm not sure if that's a signal but I haven't tried running it yet. I have the feeling it's not working.

Looks like you have the wires crossed. The constant voltage wire you rigged should be closest to the B+ terminal.

EDIT: If it were wired properly the idiot lights would turn on w/key to on.