1990 240SX Voltage Issues

[Jonathon594]

Okay so this is my first post on here mainly because every issue I have had before this I have been able to fix. This one is a tough one. I will try to be as descriptive as possible. So basically I am having voltage drops in my cars electrical equipment, mainly inside the car. If I press the brakes and my brake lights come on everything else gets dim or is affected somehow. So I am going to break down everything that I have tested and tried.

Battery Voltage, Engine Off; approx. 13v (After car has been running, I assume this is just a remaining charge from alternator.)
Battery Voltage, Engine On; approx. 13.89v

Voltage at Radio Positive, Engine Off, Key On; approx. 10v
Voltage at Radio Positive, Engine On, Key On; approx. 11-12v (Should be 13.89v same as alternator output)

Same Readings as above at Power Outlet.

So I figured I have a short or loose connection somewhere in my wiring harness.

Here's the weird part, I am only getting 10-11v at my amplifier with the engine running. It has a cable straight from the battery to the amp.

So now it makes me wonder if I am having a ground issue. So I tried a couple more tests.

Battery Positive to Body Ground (To see if my ground is bad), Engine Off; 13.20v
Amplifier Positive to Negative, Engine Off; 13.20v (No Difference)

So some history about the car's electrical issues.

Dash Lights Never worked, Turned out that their ground wire was getting 12v. (I made a new ground)
Brake Light always makes headlights go dim
Blinkers, Flashers, Headlights, Brake Lights, All make Temp Gauge go up.
Front Engine Wiring Harness got ate by the clutch fan. (I rewired it but I do not think this is the problem because it worked fine after)
Recently the Automatic transmission control module (Useless POS since my car is manual now) fried itself and burnt up the connected. this is about when my problems got worse, but I have removed the computer and cut all wires. (Fixed the problem of my engine shutting on and off while driving, But I still have voltage drops)

I pulled the entire dash and check all the wiring. it appears to be good.

My lowest voltage reading was this
Power Outlet Reading, Engine On; Radio On; Amp On; Vollume Max(Listenable); Brake Lights On; Interior Fan On; approx. 9v (Nothing works on 9v in a car, my radio was choking on itself and engine was choking too.)

It appears that the voltage drops do affect the engine in some way, I don't think its the fuel injectors, but the Ignition Coil might not be getting enough power. When the voltage drops the engine seems to idle down and sputter.

Please let me know if you have any ideas or if you need me to test something else. Ive all the time in the world and I want my car running right. Any help is appreciated!

[PapaSmurf2k3]

I had a big response typed on my phone and I got redirected to some ap service (which deleted my post... ugh).

Anyway, Welcome to NICO! That certainly sounds like a dilly of a pickle you've got there. Thanks for the detailed description.

The bogging you're experiencing could be due to the alternator simply struggling to meet the commanded voltage, thus putting an extra load on the engine. That coupled with the lower voltage also makes the spark struggle like you mentioned.

Have you ever replaced the alternator? Do you have a battery you could try swapping in? Those would be easy things to cross off the list if possible. I've seen batteries have an internal short, causing everything to work harder. Does the battery get hot?

My next suggestion would be to put a multi meter inline with the battery to see how many amps it is drawing. If its above like 50 or 60 milliamps, you have an issue. From there, start pulling fuses to see if there's a smoking gun that makes the amperage draw drop down to acceptable levels. From there you know which circuit to look at, or replace a wire, etc.
Good luck man, let us know how you make out.

[Jonathon594]

I forgot to mention, Battery is Brand New, I had alternator tested it appears to be good and it puts out 13.9v.

Anyway I did the amp test from neg battery terminal to the ground cable. these were results

First time after removing cable, key off. -150ma Only for a split second then went to zero, cant replicate the effect. (Negative because multimeter cables were backwards i guess.)

Key on; with engine electric fan running; 1.5 amps

Key on; engine running; only like 0.5 amps

[PapaSmurf2k3]

Weird, it should be more than zero even with the car off. Do you have any data for key on, engine off, fans off?