Headlights Low Voltage

[Pony Boy]

Having an issue with dim headlights and instrument cluster lights that will also flicker enough to notice at random times, and will also dim noticeably when the brake lights go on. It's on an '88 Ranger, I didn't have this issue until my alternator shorted itself out a couple years ago, and melted some of the main power wire running from the alternator to the wiring that runs behind the radiator, that has since been repaired.

Checking voltage at the battery with engine running I get 14.4 volts, no issue with the current alternator. Checking voltage at the headlights with both lights plugged in I get 10 volts. If I unplug one headlight and check voltage at the headlight plugs again I get 11.2 volts. If I unplug both headlights and check voltage at the headlight plugs I get 13.2 volts.

Wire harness grounds at the radiator support have been cleaned and verified to be good. I'm not sure where to head next with my troubleshooting.

 

[Uncle Gump]

Being that you also have issues with dash lights... I would start by looking at the headlamp switch connector.

I've seen those melted from heat in the past.

 

[sgtsandman]

Agreed. Look for the common denominator(s) since more than one thing is effected. If you have a wire diagram, that would help figure what shares what.

 

[RonD]

Yes, +1 ^^^

You don't mention it but your profile says 1995 V8 conversion
Did you do it or did you buy it this way?
Do you know if it has the Ranger engine bay fuse box or the Explorer fuse box?

Main light switch has full time 12v(battery volts) from a fuse in engine bay fuse box
Key off
Test battery voltage, remember it
Test unplugged Main light switch connector wires, only 1 should have 12v, and should match Battery Volts EXACTLY
If not, wire is bad, could be under fuse box, corrosion, there should be no "splice" in the wire but if its a V8 conversion.....................

If you have full battery volts, plug connector back in and turn on head lights, test headlight connector for full battery volts, if lower get a new Main light switch, most likely issue

 

[Pony Boy]

My profile is referencing my old '95 Bronco I had way back when I joined. The Ranger is original other than a 2.3 turbo engine swap, no changes to wiring or fuse box.

Headlight connectors are far below battery voltage, I know that much, with both headlights plugged in I get 10 volts. with both unplugged I get 13 volts at the headlight connector. I'm not sure why I'm getting different voltage readings when the lights are plugged or unplugged, that's kind've messing with me.

I did remove the headlight switch to check the connector, everything looks fine, no melting, etc. I'll check the voltage running to it in a bit.

 

[RonD]

Its called a load/voltage drop

There is a bad connection that can only pass a few amps, so when you test with a Volt Meter, which has under a 1 amp draw, voltage is high(battery volts)
If you add a bulb with say a 5amp draw then voltage drops, but not too much
Headlight circuit should have 20-30amps available, what ever its fuse rating is

Since Volt meter's have almost 0 amp draw when you are testing wires, with out load, you should see EXACTLY battery voltage
Even 0.2v drop would indicate a problem at a connection
So test battery volt with key off, OR with key on, it will be different, and then use that as your EXACT voltage to test for

Corroded wire ends or splices cause amp limits
Light switch can have dirty contacts inside causing same thing

And battery itself can be an issue, but if you test with engine running that will take battery out of the picture
Test battery voltage engine running, that would now be the "sample" voltage you should see at any "12v" wire you test if it doesn't have a "load"

12v battery is 12.8v new, 12.3v when it needs to be changed, 5/6 years
Alternators minimum voltage is 13.5v
So with engine running the battery is no longer being used, voltage is flowing to the battery to keep it charged
So the whole vehicle electric system is now running at Alternator Voltage, say 14volts, but test it at battery to see EXACT voltage

 

[Pony Boy]

Power wire running to the headlight switch is exactly what my battery voltage is, 12.57 volts. Plug the switch in and I see 10 volts at the headlights. I ordered a new headlight switch as my next step, we'll see if it makes a difference later this week.