Hello everyone, my '99 4-cylinder 2WD has some sort of alternator issue where if I leave the 30A fuse for the generator/alternator inserted after I shut the car off, the battery light turns on in the dash and the battery is drained overnight. If I remove the fuse, I have no problem, but obviously I can't drive like that.

I want to build a fuse bypass switch like they did in this video, but this and other tutorials use small fuses (10A or less). Would I be able to use the same method to bypass this fuse? I don't want to replace the alternator because it still works just fine. I've even disconnected the battery while the truck is running and it runs fine. Thoughts?

https://livinlite.net/stop-pulling-f...tow-a-vehicle/

 

Welcome to the forum

The voltage regulator IN the alternator is bad

And it will most likely smoke your battery over the next month or two by over-charging it

The 30amp fuse is just the Voltage regulators monitor circuit, and it should be OFF with key off, inside alternator
The fuse always has 12volts, but is disconnected with key off inside the alternator

First test battery voltage, key off, should be 12.3volts to 12.8volts
12.8v is a new battery
12.5v is a 3 year old battery
12.3v is a 5/6 year old battery and time to shop for battery sales

12.2v or lower is a dying/dead battery

Start engine
Test battery volts again, should now be 14.3v to 14.8volts, about 2 volts higher than key off volts, but NEVER EVER over 15volts, this is Fast ReCharge
Let engine run or go for a drive and do NOT shut off the engine
After 10minutes of running/charging retest battery voltage, engine still running, should now be 13.5v to 13.8volt(slow charge), if its still over 14volts then alternator is "cooking" your battery, so it won't last long

So doesn't matter if you pull the fuse or put in a by-pass you will have to replace battery AND alternator in a bit


The Yellow wire on the 2 or 3 wire plug-in on the alternator has the 30amp fuse, only way to by-pass it would be to CUT that wire and install a key on Relay to connect it


1999 charging system wiring here

B+ is the Stud connector on the back of the alternator, the Bigger wire

Yellow wire(A) and Light green wire(I) are on the 2 or 3 plug connector, 4cyl Ranger alternators often didn't have the White(S) jumper wire(3rd wire), it was internal

You can replace just the Voltage regulator on some model alternators, not all but some, and its not hard to do

And try pulling Fuse 15 in cab fuse box to see if drain stops, it could be a cab wiring issue, fuse 15 is the ON/OFF switch for alternator, the light green wire/battery light circuit

 

Hmm, OK. Thanks so much for taking the time to write all that up. Very thorough. Since it's almost sleepytime where I'm at, I'm going to leave the voltage regulator fuse (30A), pull Fuse 15, and let it sit overnight to see if the drain stops. Thanks for the tip. Then I'll try your methods. Honestly I would want to replace the battery and alternator but don't have the funds right this minute.

 

But alternator could ruin your perfectly good battery, which is what you want to avoid

try car-part.com

Used alternators are not expensive, maybe $30

To test leave 30amp fuse in, and with key off just pull fuse 15 in the cab to see if battery light goes off, it should