flickering headlights/instrument panel lights

[cammeddrz]

i have a 1988 bronco II v8 swap completed a year and a half ago but i left all lighting wiring un-molested

i am experiencing flickering headlights and instrument panel lights (taillights could be also but i can't see those) , not just at idle either i can rev up the engine to 3,000+ rpm and they still flicker.

the alternator is making 14.5volts at idle, and the battery is good and holds 12.5volts when load tested

for diagnostic purposes i ran a wire from one of the instrument panel light sockets straigt to the battery. that gauge lights up without flickering while those still wired to the inst panel lighting are flickering

if i shut off the truck they stop flickering as well

my truck has a huuuuuuge lumpy cam

it sounds to me like something that is vibration related

thanks in advance :icon_thumby:

 

[Earl43P]

Your alternator may be passing AC volts into your DC system. Replace the alternator.

I'd clean up all the grounds first, but I'm 99% certain you have a bad alternator (bad internal diode).

 

[cammeddrz]

if that were the case the battery lead that i hooked the one into which was actually the main post on the back of the alternator would have also caused that light to flicker right?

i'm pretty sure that the problem is after the alternator, but before the lights themselves

but i'd easily be able to diagnose that the alternator's rectifier was failing and causing ac voltage to bleed through by starting it and then disconnecting the main lead from the alternator and seeing if the problem goes away, or if it persists right?

 

[Spott]

Loose battery terminal clamps can cause vibration-related flickering. After that, I'd check grounds, then the alternator/regulator.

Although, your voltages indicate that your wiring and alternator may be in proper order. If you had an oscilloscope, we could really dig into it, but I doubt you do.

Spott

 

[cammeddrz]

ok, battery is tight with clean terminals, always was. i started it up and they flickered, i un-bolted the main battery lead and they still flickered. i re-connected it and drove down the road, even the slightest bump makes them flicker (like basic driving down the road, or the lopey idle of my cam). i got going, kicked it into neutral, and shut off the engine........they still flickered

i have deduced that it is not alternator, and not the grounds because i only needed to move the positive side to a different lead to make it stop

 

[Earl43P]

Grounds can be tricky.

The original Neg Battery lead went: B- to rad support (small lead) and B- to frame, then engine block (all in one large lead). Your symptom may be casued by a lack of B- to frame because aftermarket leads typically skip the frame connection and go straight to the block.

You could experiment by using a set of jumper cables: connect black clamp to B- and its other end to block, then frame, then chassis to see which connection is compromised. Another option is B- to the individual grounds on the rad support and fenders.

I suspect that your rad support / fender grounds path is the issue; their ground path could be flowing through the cab bolts to frame through engine mounts to block rather than a proper ground (check the small lead to rad support and the rear cylinder head to cowl - WS wiper motor bolt).

Just a guess though. You've done some extensive mods, so it stands to reason that a ground could have been missed / compromised. Quite the ticklish problem you've got!

 

[88_Eddie]

i had this same problem on my 88 BII. there was a frayed wire on the actual headlight knob. i could not find the damn thing anywhere, so i just took it somewhere. the shop charged me $450 to fix $1 worth of wire.

 

[cammeddrz]

yes i have done "extensive mods" but i'm certain it is not ground related, my gauges are all aftermaket in a new panel, they all share a common ground that goes to a bolt inside the dash. the 1 guage with the hard-wired positive was not flickering when the others were, i reiterate: they share the same ground. if it were the ground it would not matter what i did with the positive.......

not to mention the headlights do not share a ground with the instrument panel lights.

 

[cammeddrz]

eddie that is the first thing i've heard yet that makes sense...........which wire was it? was it in the connector that plugs into the switch?

 

[gwaii]

those headlight switches are known for failing in this manner.i'd be willing to bet if you looked at the plug on the switch,you'll have at least one wire(power in or headlights out)that is melting the plastic on the plug.
the female spade connector heats up and loosens,so it makes intermittent contact with vibrations as you've described.

edit...i'd put money on it that there's discoloration/deformation around the black/orange wire on that plug.

 

[88_Eddie]

eddie that is the first thing i've heard yet that makes sense...........which wire was it? was it in the connector that plugs into the switch?

cant help ya there man, like i said, i just took it to a shop eventually. i searched and searched and searched for that damn thing. i couldnt find it and eventually the headlights wouldnt even work, so i took it to my local guy that does some of my work. they found it after about 5 hours of troubleshooting. i'm about 90% sure that it was one of the wires that came off the back of it (like gwaii said). this happened about 6 years ago, so i dont really remember exactly what the final diagnosis was.....just that i should've been able to find the damn thing.

 

[cammeddrz]

ok gwaii, eddie. you both have me excited to get off work and go and try this.......i just may finally have a solution

 

[88_Eddie]

ok gwaii, eddie. you both have me excited to get off work and go and try this.......i just may finally have a solution

good luck, hope it works for ya. glad to hear i'm not the only one screwing around here at work. lol

 

[cammeddrz]

not switch, which wire should i be chasing all through the dash/firewall to locate a problem?

 

[Earl43P]

I just looked at my 90's junction box under the hood. I noticed that all the fuses are fed power by a small jumper wire. Mine is pretty ragged looking, with insulation completely missing in spots. Not good for a power wire, but it is unable to hit anything to short out.
Might look at that.

http://www.therangerstation.com/tech_library/WiringByColor.html