Turning Headlights Off Kills Engine

[Jrod1774]

So, i have a 1991 Jeep YJ with the 4.0 engine, it's pretty good, works really well, reliable, etc.

Recently it has developed an oddyty, 2 or 3 times out of 10 with the engine running and headlights on, when I switch the lights off almost kills the engine, it almost dies and after like 2 seconds pick it up. Like I would have disconnect the coil for a second.

I cleaned all the grounds, repair (clean and restored) the rheostat, there's no weird radio wire, and still does it.

I also try running it with the rheostat disconnect before the cleanup and it didn't die, but maybe it was just for the times I try it.

Any help?

 

[dieselearl]

alternator going out. bad battery or could be a ground wire.

 

[Jrod1774]

alternator going out. bad battery or could be a ground wire.

I'm thinking it's the alternator because it was from one day to the other, I mean, no cables were messed around to suddenly be bad, although I put a voltmeter and it's charging fine. Steady almost 14 volts

 

[Flyer58]

Does your YJ have the wire harness upgrade with a relay? The headlight switch is also a circuit breaker and can overheat and fail. OEM incandescent headlights draw a lot of power through that switch and wires. When you turn off the lights there may be something funny going on inside the breaker/switch causing a momentary short circuit.

I guess you can try jumping or bypassing the switch, if it's safe, and cycle the lights a few times to see what happens but there may be a chance of a short downstream with the wires to the lights. Don't burn stuff up.

Most people switch to good LED headlight which use less than a third of the power over the original and / or add the upgraded wire harness with a relay.

Either one of those upgrades won't fix a broken headlight switch.

my 2 cents along with coffee.

 

[Jrod1774]

So I measure the alternator when it did the thing and voltage stayed at 14 (I guess this is good) so no bad alternator.

Try another headlight switch (a good original Delco Remy I had laying around) same thing.

Cleaned the headlight grounds, no change.

Try with no rheostat, same thing.

Wiggle around the thick wiring harness under the dash and the it's started dying when turning the headlights on but then returned to when turning it off.

Ps. I don't know WTH is going, buuuuuut, coincidentally it started doing this after I changed the tps, map, and cleaned the throttle body and iac valve, also put new gasket. Before the new sensors on the morning it's started on the first try, now it does it on the second almost third, but just on the mornings, after that on the day it's starts fine. Sooooo, does any body has a bullet?


Edit: After like an hour thinking, as the wiggling of the harness kinda did something and this cables go around the fuse box, I'm going to remove the fuse box and see if there is any damage wire and clean up the plugs.

 

[dieselearl]

i would go back and recheck the areas where you done your repairs.the fact it was ok before the parts replacement, alternator under load will check different than idle check. you might have to take alternator to auto store, they can check both ways?