michael26la

89 p/u 4x4 v-6 .. when headlights are turned on engines lugs down and begins to miss badly. only happens with headlights on.. Alternator and battery checked out good .. i feel it is grounding out somewhere. but unable to locate the problem.. Any help would be greatly appreciated..

xxxtreme22r

When you tested the battery and alternator did you test them in the truck or did you take them out to have tested?

Could be just bad battery terminals and/or chassis grounds.

If the head lights were grounding out somewhere you would be blowing those fuses.

How new is your dizzy cap and rotor? With the head lights on it draws more current that takes away from the electrical system and if your cap and rotor are not in good shape the spark might not be strong enough to jump between the rotor and cap if they are wore out.

michael26la

alternator and battery were checked out of the vehicle. new battery terminals installed recently. to my knowledge the rotary and cap have never been changed. i'll have a look into that suggestion. thanks for your thoughts and time..

sam333

Does it only happen at idle? If it does check that your idle up is working.

michael26la

it does it at any speed when i turn the lights on.. and immediately stops when i turn lights off..

xxxtreme22r

try having them tested while in the truck, that will tell you if any of the charging system wiring might be a cause of the lack of electrical power. I would do that first, but it never hurts to change the dizzy cap and rotor.

sam333

That is a real interesting problem ,because the two seem so unrelated.
I could see it if your alternator quit working, and the battery slowly discharged till the voltage was not high enough to power the ignition system( and that does happen) , but the battery usually takes up the slack( ignition still works) till it runs down. I would test your alternator under load, but no missing (just no lights) at idle to 3000 rpm and make sure your getting 13.5-14.5 volts. Then I would disconnect your alternator( take the belt off) , start it and turn on your lights and see if the missing stops( electrical noise).

xxxtreme22r

please do not run your motor with the alternator belt off. That same belt runs your water pump !!!

Moonfish

https://www.yotatech.com/forums/f116...rite-up-33526/

It only costs like $12 and half an hour. The factory wires are pathetic once you cut the insulation off of the wire feeding the fuse box, you will understand.

sam333

You can run the engine without the water pump for a minute for testing and it wont hurt anything( just do it cold).