1978 FordF100 Ranger 302 engine c6. My headlights are flickering diming don't know why? Please hel0

 

is it happening at idle and go away as engine speed increases? Is it a consistent flicker, or is it random? Does it change if you push the dimmer switch? both headlights?

 

yes both headlights inside cluster lights as well its consistent

 

my first guess is alternator issue (rectifier or possibly regulator). my guess is the flickering will stop with the engine shut off...if it still flickers with the engine off, then you have a loose connection someplace. if ONLY the lights associated with the headlight/illumination circuit are affected, then it could be a bad headlight switch/associated wiring.

 

That's great advice from dlburch. Likewise, I would think alternator if it does it when running then headlight switch if it does it when not running and just on battery power. I think i've replaced just about every headlight switch I've had in an old car so that would be my default answer if I didn't know.

 

Check voltage at the battery while they are flickering. Battery voltage should be near constant, but if all over the place, could be a voltage regulator.

 

All good info from above, I would lean more towards vr as I had the same issue on one of my older ones and a new VR did the trick. Also, I would order one of these and install, cheap and only takes about 2-3 beers for labor installation did it on my 66, got one for my 63 and both my 77's, makes a huge difference.

https://tomsoffroad.com/parts/66-77-...wiring-harness

 

I have never changed the light switch its the original switch. Im restoring this truck had been sitting for about 20+ years before i got it going a couple of years back the alternator was replaced rite before it was parked

 

Great advice already given, all I'd offer up, on the chance you might not know, is if you have a multimeter, measuring across the battery terminals at high idle should be in the 14v area and pretty steady (assuming a high steady idle)

If you don't have a multimeter even the cheapies (that they used to give away) from Harbor Freight would work. I have a good Fluke meter but at $7 the Harbor Freight meter works better than I would have expected, just don't try to measure voltage if you have the meter switched to measure resistance (Ohms). The circuit isn't voltage protected and it kills that resistance measuring part of the meter, though voltage measurements will still work,....and I wonder though what practical experience I figured that information out :\

The charge discharge gauge on my '72 250 essentially never does anything which I've read here is common, so I picked up a cigarette lighter plug in device that reads out voltage which allows for random checks without pulling out the multimeter. I don't leave it plugged in when the truck isn't in use, just pull it out of the glove box for a spot check. The bonus is it also has USB ports, though I haven't had need to test them yet, and I'm not sure how well (how fast) it would respond to trying to trouble shoot a fluctuating voltage issue. At $13, it works for my needs. Just a thought.

 

I have many years ago experienced similar on a 1975 dent side F250, alright on first minute or two then problems, the switch was hot to touch after a while, new switch, all good!
How old is your swich, also check for good headlamp fuse contact, feel for heat at all headlamps wiring connectors when lights have been on a while, could just be a poor connection.

Goodluck, Ross.

 

original switch

 

Don't forget the floor mounted dimmer switch.

 

you talking about high beam switch?

 

Yes the drvs side kick panel (well real close to it) headlight high beam / headlight dimmer switch is what he is talking about.

 

that works fine,