Hi all, I recently did this upgrade:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/how-1979-alternator-upgrade-967330/

I'm having issues and I'm hoping someone can point me in the right direction for a fix.

Firstly, I followed the narrative and wiring diagram and used a reman S4 alternator. I did a continuity check on all the wires excluding the choke and cluster wire simply because I don't want to try to get to them yet. I'm competent with wiring and soldering as I was an avionics technician in a past career. I checked voltage and the battery is charging at a normal rate. The choke is also working.

The first issue I'm having is my voltmeter doesn't work. Not a huge deal but annoying.

The second issue is I found that my battery was draining while parked and key off (obviously). I found that the 4 pin relay would cycle when the battery was connected and would draw about 0.15A. I have disconnected this relay for now and found that the alternator auto-excites fine.

I would like to connect the auto excite wire so that it works as intended and get the voltmeter working. Any suggestions would be greatly appreciated.

 

I know this a little older, but I am having the same issue. If I drive it everyday, the battery drain isn't an issue. If I don't I have to charge the battery.

Voltmeter doesn't work, which isn't a big deal for me as I have an aftermarket gauge.

Mine since doing the upgrade has never auto-excited. I have to rev to 3k rpms for the voltage to jump to normal. Not an issue so much as these carb'd cars need a little rev to keep them running initially.

So disconnecting the 4 pin relay saves the battery from draining? Any other issues caused by doing that?

 

I ran without that relay connected and manually excited the alternator like you're doing for a little bit. I ended up wiring everything back up the way the guide said to. I found my battery was going bad and that contributed to the issue. I keep meaning to go through the wiring and find a better switched +12v wire but I haven't yet as I drive my car almost every day and the drain doesn't cause issues over short periods of time. I think the switched wire the guide uses is not switched and is causing the relay to always be hot but I haven't dug into it to verify.

 

Its also a symptom of a weak battery, it may not be draining but more like not holding the
charge like it should. I just went through a similar issue where a weak battery finally took out
my alternator, so I swapped in an S4 (plug and play on an 80 SA). Didn't replace the battery
at first and had the same symptoms you all had. After replacing the battery, all is good.

 

My battery is a year old. Had it tested and it is supposedly good. When running the voltage is right about 14 volts.

 

14v is a little high. You should be in the 13.5v range when charging. Over voltage is an indication that a cell in the battery is going bad and the alternator is trying to compensate.

I'm going to dig into my system when I have some time off and get back on the relay drain.

 

Always been 14 volts or so even with the old setup with the regulator. Even in the Haynes manual there is a range of 14.5-15.5 volts!

 

13.5v is too low for a healthy charging system unless it's got a massive drain going on - - it's the minimum full-load test voltage for a stock alternator per the FSM, under a 40A load. It's barely enough to bias the battery into a charge state.

13.8-14.4V is nominal charging voltage for a lead-acid 12V battery.

 

Alright, I was a little off on my recollection of correct battery charging voltage which may be effected by the fact I've always lived in hotter places which causes lower voltages. Still, an over voltage is indicative of a cell going bad.

 

I had this exact same issue. Draining battery, low charge rate.

Can you show us a picture of the wiring/plug for your alternator? I bought what I THOUGHT was a S4 alt (and was sold to me as a S4 alt) that turned out to be a S5 alt. The S5 needs a CONSTANT hot from the battery where the S4 takes a switched hot. If you have it hooked to a switched hot, the battery will drain when the car is off.

It took me 2 years to figure out the issue.

Also, when/if you wire up this constant hot, wire it directly to the battery- you want a clean signal, which will give you a proper charge rate.

 

That's interesting. I too bought an "S4" alternator but I'm not sure now. Here is a picture of the back of mine. The small plug hole hidden behind the wiring has no connector. I was out of town for about a week and my car wouldn't start when I got home due to a dead battery. Didn't realized it was so bad as I drive the car almost every day. If you can let me know if this is an S4 or S5 alternator I would appreciate it.

 

Need a pic of the whole alternator. S4 alternator has that same 2 prong connection but the main battery connection doesn't look right from your picture. If you look on my S4 alternator the battery connection is mounted horizontal.

 

The battery connector is made so it can be rotated if needed.

 

Mine has that same plug adapter like that- can you show me where the wires actually go into the alternator? I'm willing to bet it's got an S5 plug.

 

This is what mine looks like overall. Again it was sold as a reman S4 and I have static drain and low charge rate.

 

That sure does look like an S4.
I guess the only way you could really know is make a jumper (with a fuse) directly from the battery to the switched hot and see if that solves the problem. If not, it's likely just a bad diode in the voltage regulator.