1986 4.9 300..lights(all)flickering and amp gauge flickering (rough idle)put in new light switch,lights still flicker....while the truck was running i unhooked the battery cables and the truck kept runnung,the lights STOPPED flickering and so did the gauge,also idle seemed a little smoother....(also new battery)..voltage regulator?alt?starter switch?need some input..thanks

 

Why did you start a new thread for this?

With the truck running and the battery connected, measure the voltage across the battery.

 

ok..engine running...(13.20)....ENGINE OFF (12.80)

 

Those numbers sound good. Your charging system seems fine.

Do you have a ground strap from the firewall to the engine block? This is how your entire electrical system grounds. The negative battery cable goes to the block, but the block mounts to the frame in rubber. There is no electrical connection. It sounds like you might have a grounding problem.

 

yes there is the ground wire(firewall to block)also had the alt checked.shouldnt the volts go up to maybe 15 when reving the engine?seems alittle low to me.guess i will try putting all new ground cables on also..as you say it might be a ground prob..why though when i unhook the battery does the flickering stop?and idles down.thanks again fmc

 

The only reason I can think of as to why your idle and flickering changes when you remove the battery cables is because the signal seen at the 'A' terminal of the regulator goes open circuit, which would change the output of the alternator. Because of this, and the fact you told me you have a good ground strap to the firewall, I think your problem is local to the regulator or the wiring. The regulator is bolted to the passenger side fender well, and the wiring harness at that point is subject to a lot of stress because of heat and environmental factors. Mine always get stuck with leaves, etc. What I would do is remove the wiring harness between the regulator and the alternator and keep track of what goes where. I'd use a multimeter to ohm out each lead - you should have A (alternator), F (field) and S (stator). Make sure you've got good continuity between each end. The A, F, and S are marked on the regulator themselves, and A, F and S are marked near the posts on the back of the alternator housing. Also, you can have your regulator checked out at most parts stores that check alternators, ignition modules, etc. I've had bad regulators that checked out good before, though. If I had to guess, I'd say the problem is central to the regulator or the regulator\alternator wiring harness.

I still think your voltage numbers sound good. When you rev the engine, the voltage won't climb much past 14. 13.2 at idle is just fine.

 

Fmc thank you for taking all the time you have to type and explain things,its truly appreciated..today I ran a wire from the firewall to the voltage regulater and bingo the lights stopped flickering(there already was a ground wire hooked up)then i drove the truck for about 2 miles and the gauge is starting to flicker again not as bad as before though..I also replaced the light switch and checked dimmer switch....so as you said im thinking it probably is the regulator....I am going to try what you said..and see what happens...Thanks again