59 F100 Dual Headlight Electrical issue.

[janschutz]

My wife's 59 F100 has dim headlights. Someone before me replaced the electrical harness with one from American Auto Wire.

I replace the headlight switch 3 years ago (the old one did not work). I moved the wires one at a time (Does not mean that it was wired correctly).

When the low beams are on, there is 8.97 volts from the hot wire to the ground wire. At High beam, there is only 5.5 volts from hot to ground. When the High beam is on there is .34v on the low beam hot and on low beam, there is .18 volts on the high beam hot.

Tomorrow I hope to be able to pull out the light switch and check it. I also plan to run another ground wire for each headlight. Also I need to find a pin-out for the headlight switch.
Any more suggestions?

 

[janschutz]

Found a light wiring diagram.

 

[kb3]

Where are you measuring voltage? You should have a solid 12+ volts going to each light. The difference between high and low beam is the lights wattage, but both use 12v. The AAW harness on my Mustang uses relays so you get a much bigger wire going to each headlight instead of the small gauge wires going through the headlight switch, therefore more power to the lights.

 

[Horseplay]

Throw all those wiring diagrams away. Just wire it up correctly yourself. It's a super simple circuit. Have the output wires for the low and high beams power the coils of their own solid state relays. Have a direct wire from the battery source go across the common contact on each relay. Run a 12 ga wire off the NO contact to the headlight bulbs. Make sure you have good clean grounds and your lights will always be bright. I would suggest a fuse in each wire headed out to the bulbs in case of a short. Fusing them this way would allow the lights to function on either hi or low if one line fuse blew so you could safely drive in a pinch.

 

[Midlife]

When checking voltage going to lamps, you have to make sure all of the actual lamps are removed from the circuit to truly test the voltage. I'll bet you have a bulb with an internal short or other issue. Check one bulb at a time and see if you can isolate which one.

 

[B67FSTB]

When operating the lights , first check if you get 12volt to the lightswitch. Then check the low/high beam switch imput/output. Check also if your bulb are the right voltage and wattage. If all is OK , check the lights wiring from the lightswitch to the lights. Maybe the wiring has some sort of short , meaning some resisitant.

 

[Horseplay]

The old wiring harness designs and wire used for headlight circuits can be GREATLY improved and provide much better illumination if you do as I suggested earlier. You're not trying to keep the truck stock so why not make it better and SAFER? Your headlight switch will thank you for taking that huge load of too!

 

[B67FSTB]

Using solid state relays is of course the better way . You then can make use of halogen light bulbs. Make sure you put a circuit breaker near the pos pole of the battery for safety.