When I turn my lights on or my heater on high, my idle drops, is this normal. I just bought the car and it had a group 27 battery, I just installed a red top. It did not change anything. Thanks

 

Normal to a point,electrical accessories when turned on put a load on alternator which is driven by the engine,which in turn loads the engine causing the idle to drop some,maybe 200 rpm or so. Once the car is running the size of the battery isn't critical, the power to run the car comes from the alternator until the accessory load exceeds the output of the alternator then the battery suppplies what is needed. Have you tested,or had charging system tested on your car ? Any aftermarket hi amp draw accessories installed,stereo amps,subwoofer? What yr. model RX?

 

What are dash voltmeter readings with/without accessories on?

 

I have an amp, I think the voltage gauge reads around 14 volts

 

Sounds pretty much normal,wouldn't look for trouble where there. may not be any. Drive/enjoy the car,keep an eye on voltmeter,see which needle fluctuations are normal,that way you'll know when something changes and needs attention. Post a pic of your car.

 

The stock alt is pretty weak. Adding extra draw like an amp will bring it to the edge. Did you try
all of this with the amps off?

FWIW, the rx7 S4 alternator is a plug and play replacement that get you 70 amps (up from 55).

Also make sure all your chassis grounds are good and tight. Including the rear one to the muffler
from the body.

 

Would imagine the 14v reading is with without much in way of accessories running.