Write-up: S4 to S5 alternator conversion (please rate for archives)
 

ok i just finished up the S4 to S5 conversion for my alternator on my 87 GXL and all is good to go with voltage hitting 14.4 on the dot.

the process is pretty simple for the mechanically inclined but there are a few quirks you should be aware of.

1) the plugs for the S4 and S5 are different, the plug in the Back of the S4 translates to the Top of the S5.

a) On the S4 you have a horizontal female connector on a black wire with white stripe, this wire goes on the passenger side of the S5 clip. The vertical connector is a white wire with a black stripe, this of course goes on the drivers side of the S5 clip.

https://www.rx7club.com/forum/attach...&postid=935289

b) the easiest and safest way to put the S5 connector on the S4 harness is to take the female connectors out of their housings. to do this you need something stiff, about the size of a toothpick (i used the flatblade screwdriver from a glasses repair kit) you take the instrument and press down the tab on the folded side of the female connector and slide it out through the rear of the housing, it should, in all cases, slide out easily so dont force it (this sounds very sexual) Once you have removed the wires from both connectors, just switch them in the proper manner as described above.

2) the top post on the S4 alt is much much smaller than that of the S5, you will need to cut the ring terminal off of the S4 harness, and buy another one capable of fitting over a 1/4 inch post and taking an 8 ga wire. (i used a battery cable end, not the main post but the smaller one)
crimp it on and you are good to go with 10 amps more than before

hope this is helpful to someone

thanks
Justin

does it fit under the strut brace?

I was looking at putting an s4 alternator on my s5 (can get one cheap), is it worth it to get the s5 (probably a $100 difference)?

Is the s5 any better than the s4? They are both rated 70 Amps @14v so why would anyone do this unless they had to replace their s4 and could only get a s5?
Chris

I too have added an s5 Alternator on my s4 with the addition of a 10 gauge wire from the Alt to the Battery. Have seen voltage go up 1.5 volts due to this.

The s4 Alternator Is mundane at best. Everybody that has an s4 should do this simple conversion.

BEFORE YOU DO THIS MOD, READ THIS POST!
 

There is one problem with putting the S5 alternator into an S4 car...battery drain.

The S4 alternator has an internal relay that disconnects it from the battery when it is not generating current. The S5 alternator DOES NOT HAVE THIS RELAY. The end result is that the S5 alternator will slowly drain the battery if you do not run the car often.

From my experiance, it takes about a week for a perfect battery to go from 12.5 volts to 0. If you start your car everyday, this won't be a problem. If you plan on storing the car for more than a week, go ahead and disconnect the battery.

Another solution would be to attach a 12v relay in line with one of the wires on the Alternator plug. Have the relay open and close with the ignition.

You've been warned! ;)

Jeff

PS: Yes, an S5 alternator will fit under the strut bar. I've have a cusco bar on my car with no problems.

does the connector from the s4 alt plug directly into the s5 electric connector spot? they look to be 2 different sizes from the pic above.

Re: BEFORE YOU DO THIS MOD, READ THIS POST!
 

[QUOTE]Originally posted by wozzoom
[B]There is one problem with putting the S5 alternator into an S4 car...battery drain.


Couldn't you just disconnect the Alternator harness If you plan on storing your car for over a week?

Correct, they are two differnt sized plugs. You need to get the S5 plug for your S4 harness if you plan to do this mod.

Re: Re: BEFORE YOU DO THIS MOD, READ THIS POST!
 

[QUOTE]Originally posted by silverrotor
[B]
I guess you could do that to. :) That way you don't loose your stereo/clock settings...

wozzoom:

Could you elaborate on drainage. I was under the impression both s4 and s5 have a check relay inline with the ignition switch. See pics attached for s4. s5 follows.

Regards,
hugues -

here's the s5 alt

I would like to correct my previous post. The check relay has obviously nothing to do with potential battery drainage (it is for the charging light).

I think I now understand why there could be a drainage problem:

the s4 R terminal connects to battery + after ignition switch

the s5 S terminal connects to battery + before ignition switch

Never noticed that before. I guess I should have known from different name for the plug terminals.

Leads to more questions. Would you get drainage even if all diodes are not leaking ??

hugues -

You've got it. The S4 switch is after the ignition. The S5 is before, so it is never turned off. I believe the S5 cars have a relay else where in the engine bay that is used for this purpose but I've never traced it back far enough to find it...

Anyway you look at it, this battery drain is a problem for the conversion.

Has anyone looked at the 3rd Gen alternator? Is it similar to the S5?

I have a 3rd gen alternator on my 88 'vert. No drain problems. Easy conversion, although you have to find a pulley that is the right shaft size, or drill your existing one out. I just found a pulley. There's a write-up on my site.

www.geocities.com/rx7_ragtop

Brad

rx7_ragtop:

Where did you get your pulley for the conversion from a FC to an FD alternator? was it a stock replacement part for some other kind of car or custom? I read your write up and you didn't say what you got it from.

A guy I know over here is trying to do the exact same conversion with his FC, he isn't too big on the idea of drilling out the stock FC pulley.

Thanks man

in the write up it explains how to convert from one plug to the other.... why else would the picture be there??? did you read what i wrote or just look at the picture????

i would have rather had an FD alternator but i dont have one, the S5alt makes 80 amps rather than the S4 70, so this is an improvement, though a modest one.

would i run the extra wire directly from the alternator top post??? and do i run it to the negative or positive??? what are the avantages and the causes for the advantages of doig this??? i used to know bu have since forgotten...

thanks
Justin

This whining is from Justin's other thread....:D

Hey, we did try to help you out. Without having a S4 Rex laying around, how could I be sure what to tell you ?

Anyway, seems odd that such a simple plug would be different between two years of the same car....:confused:

Good form ol' chap :bigthumb:

oh i wasnt saying you werent helpful, i was just noting that there are more people on this forum who care about RICE than about helping other people with their woes, or learning about the RX7 for that matter

when i first came to this forum i read about EVERYBODIES problems so i could learn more in general

thanks for the assistance, remember you werent included in the chaps who failed me

thanks
Justin

I went to a local parts store with friendly folks... they found me one. I have no idea what it came from. The big chains will NOT do this.

Brad

Damn, I kinda figured as much.

Well I'll be on vacation in the states in about 60 days, my job prior to leaving the states happened to be at a small parts store. I'm pretty sure they wont mind me looking through the alternators they have in stock for a pulley, usually we always just swapped the pulleys out anyway with the core replacement.

If I find a replacement stateside I'll be sure to post what it came off of. That is unless he finds something that works over here.

Thanks anyway.

does it matter which year FD alternator you get?

I got a chance to look at a 3rd gen alternator yesterday. The plug appears to be identical to the S5 plug. It would be a straight bolt-in for S5 cars, with the exception of the pulley.

I was just looking at the pic of the two alternator, I just don't get what you are saying about a possible drainage on the S4 when you put a S5 alternator. From the looks of it, it won't drain since you need to have the key on the ignition to even get power to the Alternator, unless I'm not seeing something from the diagram. Let me know, because I had my S5 alternator in my car for over 3 years and never seen a drain after I didn't drive it over a week.

Javier