I have a 91 ranger with 2.3 engine when I push brake some time engine dies I've disconnected vacuum from brake booster still dies when pushing brake
Also if you turn headlights on and a/c engine starts running rough then dies
I've checked everything I can think of I need help

 

Welcome to the forum

Alternator is not working very well

Alternators can only make max voltage above 1,600rpm, min voltage below that, so brakes lights or ANY electrical draw at idle will stall the engine if alternator is not working well

Battery may also be draining the system, test it and the alternator

Key off
Battery should show 12.3 to 12.8 volts
12.8v is new battery
12.3v is 5/6 year old battery and time to shop for new one
under 12.2v is a drained or dying battery


Start engine
test voltage at battery again
Should be 14.1 to 14.8 volts
If not alternator is not working or very weak

 

Tested alternator it pushing 14.4 and battery is at 12.3 I've even checked voltage when a/c and lights are on voltage is holding

 

Then problem is voltage is not getting to all the parts, like Computer

In 1991 Ranger, under the fuse box are 3 relays
EEC/PCM relay, Brown base, powers the computer and fuel injectors
Fuel Pump Relay, Green base, does what it says, powers the fuel pump
WOT relay, Black base, cuts power to AC Compressor if you press gas pedal to the floor, i.e. wide open throttle(WOT)

Pull each relay and check for corrosion, WOT relay wouldn't cause the issue you are having, other two can

Diagram here: https://www.justanswer.com/uploads/l...1_234102_2.gif

Its possible the engine fuse box connector from battery is bad as well, all power, except starter motor, flows thru that one wire

You could hook up a volt meter to Cigarette lighter, and watch cab voltage while this stuff is happening, you can get a cigarette lighter digital volt meter plug in for under $15, also has USB charger, lol

 

I don't know if a 1991 Ranger has vacuum assisted breaks, but could this be a vacuum leak? Just a thought.

 

OP just go to the local scrap yard and pull an alternator off another ranger, swap it into yours and see if it fixes your issue.
Just because you have good voltage doesn't mean the alternator can push enough amps to all your accessories to run everything. Internal failure of the alternator.