Throwing this out there in case someone has seen this before, i'm not an electrical expert so i am going to take it to an auto electrician, but can be a bit difficult getting someone to check it when it doesn't constantly happen.

I'm getting 3 symptoms, maybe all related:
1. Coolant level warning light comes on, may stay on for 10 seconds, sometimes a couple of minutes. It comes and goes. Coolant level is fine.
2. All warning lights come on, again can be a short period or a couple of minutes, and comes and goes.
3. I think this always occurs with all warning lights, the voltage meter will jump up, and the radio will crackle and stop. Appears to occur with higher rpm, maybe 3-4k+, and generally stops if i let the rpm fall back to idle.
Engine appears to be running fine during any of these issues, nothing stops, no other issues seem to occur.

My thoughts were alternator, but someone else said this wouldn't be caused by an alternator issue, maybe they're wrong.

 

This issue can be caused by a failing alternator. I also recommend checking the alternator belt tension as well. The belt can slip and cause an underchsrging condition and the warning lights will come on as well, especially at higher rpm.

As for the alternator, I would check output voltage directly at the alternator. The alternator may be putting out just enough voltage to seem fine at idle but as demand for voltage increases, the alternator may not be able to keep up with the engine or accessory load.

 

OK, there's 2 belts on the alternator, they seem fine, about 1/2" give, although one seems to maybe be a little looser than the other, but i'm no expert on how tight they should be.
Not sure where to check alternator output directly, i have done some testing at the battery though, was showing:
12.37 not running
14.06 at idle
13.88 if i turned on the headlights
14.34 at around 4k rpm
turned off engine dropped to 13.5 then gradually went down to 12.65 after 2 minutes
When i had the lights on the coolant warning came on, turned the lights off and the warning went off. Maybe coincidence, rarely drive at night so not seen this before.
Anyway, anything more is probably beyond my expertise, hopefully an auto electrician can figure it out, thanks for the ideas.

 

Could be a bad ground

 

It can be a bad negative cable.....mine was bad and I installed a new one ......take it to AutoZone and they can diagnose the alternator

 

Thanks, i've had a look as best i can, can't see any obvious issues, although i'm not sure where everything is connected, battery is in the boot so a bit hard to trace the cables.
I do have some repairs coming up that will involve a few things having to be removed, so maybe something will show up then, if not i'll get an auto electrician to look into all this.

 

Ah, so this is not a stock RX7. I would suspect the cabling back to the battery first and the battery as well.

 

No, not stock, 13B turbo.
Conversion was done over 20 years ago, so maybe a bad connection after that time.

 

I had all sorts of weird electrical problems, including warning lights activating when there was no problem.
It upsets your comfort level when the check engine light comes on every time you start the car.
Also auto trany shifting was hokey. Odometer not working.. etc.
Turned out the problem was a known problem with the electrolytic capacitors on the speedometer circuit board.

There is a whole thread about those cheep leaky capacitors, and the fixes IF that is your problem.