Hey guys

Is there a specific ground that would cause no lights on dash , also no tach?
New to me SA, wiring shows a ground in back hatch, that ones good. Fuses all ck good.
Thanks!

 

Did they work previously? Start car and while running,put a voltmeter on positive and negative battery terminals and see what the voltage. Needs to be at least 13.5 volts,higher like 13.8-14.0 is better. Did you notice if the tach was reading battery voltage with key running?
Are you referring to the idiot lights on bottom of dash not illuminating or the instrument lights? Post your answers,i'll point you in the direction to go.

 

There you are bailing me out again 😁
The car wasn’t running when I had it shipped here a few weeks ago, so I’ve no idea how long the idiots-gauges have been out. Tach doesn’t move at all. Headlights work, I’ve got all dash components removed but I did see the bulbs come on when I turned on headlights.
Will ck voltage when I refill coolant (drained to replace old hoses).

 

Happy to help. Try to help people here to keep as many of these funny little cars on the road as possible.

 

Do the lights for the heating controls work? Have you checked the dimmer to make sure it's not turned down completely? Sou ds ridiculous but I've seen that be an issue.

 

Yep lights for controls seem to work, just no idiot lights or tach.

 

Do the other gauges work - water temp, fuel? Curious as I have a similar issue where on cold days only some parts of my dash work - some days the gauges read excessively high, sometimes no backlight but idiot lights work, no tach is common... Not trying to thread-jack, just curious if anything comes of this. SA here too.

At least for my case I betting on a failing solder connection somewhere.

Your non-operational tach could be the fault of the coil wire. On SA's - or actually it might only be the 80, not certain about the points system - the tach wire connects to the leading coil. Maybe look at that. Not sure about the idiot lights. Does the voltmeter work (key in 'run' position, car off)?

 

Tach wire attached to leading coil. Just upgraded distributor to an 84. Nothing from gauges.

 

Do you have a running car,did you check battery voltage while running?

 

this is probably a longshot, but I recently had issues with all the gauges and dash lights located in the instrument cluster. While investigating, I noticed many of the metal surfaces under the dash were rusty. I pulled the dash cluster out and all of the metal screws were covered in rust. I used an ohm meter and found none of the screw connectors were conductive. I removed all the screws and soaked them overnight in vinegar. After reassembly, everything worked.

the car had been sitting for several years and apparently the old weather strip allowed water into the interior and the moisture caused the metal surfaces to rust.

 

As you probably suspected, I have 12.6 v while car is running. Looks like alternator isn’t correct somehow, someone hacked wiring .
Pic of connector.

 

Alternator,wiring,voltage regulator are all possibilities.
Process of elimination...1st remove alternator and have it tested at parts store,if good you’ve eliminated 1/3 of possible faults. Take a pic of back side of alternator to show terminals.
Take a pic of front of connector that plugs into rear of alternator. The alternator wiring harness looks like someone has been into it.

 

I may be mistaken, but it looks as though the alternator plug might not have been tampered with and rather the wires were just 're-organized'. That clipped wire would appear to be from the FBVS that I notice has been cut/disabled. Now I can't tell for certain from that angle, but that's how it looks to me. Still do the tests of course, and the photos too.

Perhaps I didn't catch it earlier on, but is this a 79 car or 80? That alternator looks like an 80 or early FB unit with the internal regulator. Curious as that would eliminate another possibility once the alternator is bench tested.

Edit: I missed the extra pins on the alternator and plug at first glance so... don't mind the internal regulator/80 year bit. That clipped wire might also not be the vent solenoid's - I'm not familiar with the 79 wiring harness.

 

I’ll have the alternator tested today and post results. I also am unfamiliar with this and other things about the 79. But, it’s fun learning. If the alternator does have an internal VR, do I need to remove the VR?

 

If you have a 79, the alternator will not have an internal voltage regulator. The regulator is bolted behind the left side strut tower and can be replaced independently of the alternator.

 

After taking a second look at that photo - like I mentioned in my edit - it looks like you have the original externally regulated alternator. My understanding is that the 79's alt has four? pins in addition to the positive output. The internally regulated alternators, like those from the 80 and all later generation RX-7's only have two pins in addition to the positive output - although the function of the pins did change.

I haven't heard of someone replacing the internal regulators, although perhaps...? I've replaced brushes and bearings but never any circuitry. But no, the internal regulator would be tested with the alternator as one unit, it would not be removed.

Edit: And there I go again... That alternator, unless I'm mistaken in which case someone please correct me, is externally regulated. So you will be testing the alternator and regulator separately.

 

Yes I saw that thanks. Alternator dead. Got another ordered, but perhaps I need to take the opportunity and upgrade. I read a few threads about this, seems some debate on exactly how to do this. Some use jumpers on regulator, some install relays, some don’t. As the old saying goes, where there is confusion there is no action lol
For what it’s worth, choke solenoid was removed by PO.
Actually I was surprised how quick it started and idled with no alternator..

 

Not sure what complications the external regulator adds to an upgrade, but I'm sure some folks with experience there will chime in.

After the regulator is out of the way though, the upgrade is pretty straight forward. I believe 1980 - S4 alternators use the same wiring, and then S5 - S6 are either the same as each other or very similar. The S5/S6 alts will require a relay or diode of sorts to prevent parasitic draw after the car is shut off, which otherwise would lead to a dead battery after a day or two of sitting. The earlier alternator's don't require this and are simply wired up. Desired amperage is really what will determine which one you go with - there's a chart someone made that covers each alternator's output and connection type and what not, I'll look for it later today if I have time.

 

Update, new tested good alternator. Still no idiots or gauges. 12.4 v at alternator and battery. I have a new voltage regulator ordered, think that might be my issue?

 

If that 12.4v is when running, yeah, it seems a little low. Usually 13 - 14v is pretty normal. Could be the regulator, but as I said before, I don't know a whole lot about the 79's electrical system. Not sure if the 79 has a check/cut relay (I think that's its name), but I believe that will affect idiot lights and maybe other parts of the dash as well if not connected or working properly.

 

have u checked the wiring diagram found on the foxed.ca site? Foxed.ca - Mazda RX-7 Manuals

i'm thinking it's something to do with that wire with the bare end.

 

I have checked the wiring diagram, I have 12v and good ground at the gauges. Still something causing them not to work.
Thought I’d try the regulator just to cross that off.
New alternator is a 2 prong, came with an adapter for the 4 pin harness.
Dont think that’s the issue because old alternator had same symptoms. In fact, I question Advance Auto testing machine.. I suspect old alternator was good.

 

When you got the 12.4 volts at battery with car running,what was battery voltage without engine running. Alternator charging at the absolute minimum has to put out at least 1 volt over battery voltage in order to push current into battery. 13.4 is that number.
Good charging system on your car would have battery charging @14 volts. I agree your original alternator may have been good. Maybe have your new alternator tested at another store to make sure it is good.There is nothing like bolting on a "new good"part and thinking there's something else wrong with the car. Bad parts out of the box are not uncommon..
I would consult the charging system diagram and get yourself familiar with it. What are your plans withe the car to want to upgrade to a higher output unit? For any alternator,internal voltage regulator type included,warning lights need to be operational. Get this squared away and i can guide you to a setup that requires nothing more to have a functioning system. Do you have an idea of amp capacity you'd want?

 

Great minds and all that.. I actually took new alternator to a different store, it checked fine.
I’ve no plans for huge upgrades, stock alt should be fine. I’ll check battery voltage with car off, but I’m 99% sure it’s the same as car running.
Guess I’ll wait on voltage regulator and hope it fixes my issue.

 

Well dash lights fixed. Fuse checked good but was apparently intermittent.
Now have to replace water pump that leaked like a sieve before I can fire it up again and check voltage.