Electrical problem no high beams, Low beams fine. Ford 5030

[Exodus]

First time posting so forgive me if this is in the wrong section. Been reading the forms a long time but only just made a account. I have a Ford 5030 and it's head light high beams have been giving bother lately. On bumpy ground the high beams can just cut out similar to a loose wire, so I switch to the low beams which work perfectly. This is annoying until recently when the high beams stopped working together, lows fine. I got out the multimeter removed the bulbs and tested the bulb sockets. I'm getting 12 volts on the low beams and 12V on the high beams also strangely. I stuck in a bulb and dips work grand click the handle over to high beams and nothing, no voltage detected either it just disappeared. H4 bulbs FYI.

What I think is happening is 12 volts but no amps in the high beams wiring due to a fault/short in the wiring. I checked the fuses and relays and everything seems fine. I turned the multimeter over to measure resistance. Switched everything off and hooked it up to the high beams and starts picking up very high resistance. From what I can see it looks like the high beams positive wire is being grounded somewhere causing little or no amps to reach the bulbs but not affecting the low beams. Battery also so slowly loosing it's charge as if a light is always on I'm think it's this.

I anyone could steer me on the right path or give me some advice on what to do it would greatly appreciated. Thanks - Michael

 

[Billrog]

Michael if the + wire was grounded you'd have a blown fuse. Pull the high beam wire of you light switch and stick in on the low beam connection and see it there's light then you know if it's the switch or not.

 

[Exodus]

Yeah fuses are fine so I'm gonna check the switch. I done a resistance test to see if anything was grounded and got these strange results
View image: 20151219 124735 The negative prong is connected to the battery in all 3 photos and the positive in this picture is connected to low beams, as you can see 1 means there is no connection between ground and positive low.

View image: 20151219 124904 Connected red prong to ground at socket and black to battery negative, 0 on the tester showing a strong connection to the battery.

View image: 20151219 125031 Connected red to high beams positive and negative to battery again.
These numbers are showing there is a connection to the ground somewhere as it should show the same result as the low beams. Got all the same results with fuse removed so looks like I need to run through the harness and try the switch to see what I get

 

[Dave M7040]

Testing a circuit like you are doing with no olad on it can produce misleading results.
A bad contact in a switch or relay can send a 12 volt signal along the circuit but all changes when you ask the same circuit to transmit 5 amps for example, then it fails.
Do your tests with a bulb in the socket.
Dave M7040

 

[MrGiggles]

I agree that the circuit is best tested with a load.

I would guess that there is a point of high resistance or an open in the high beam wiring. Might be an old splice or a plug somewhere.

Make sure you have both power and ground on the high beam circuit. It's not uncommon to have power there all the time, and the ground side switched. Your schematic will tell you how the circuit works.

 

[Exodus]

Yeah I'll try with bulbs tomorrow. I traced the fault through the engine wiring harness it's in the dash somewhere so that's going to be fun to fix. Had bulbs in before and 12 volts is present in low beams when their on but no volts and no lights when high beams are on. Thanks for the input I'll update what's happening

 

[banjodunn]

G'day check your fuses and I mean physically pull it out and check I had one the other day with a hairline fracture that was allowing no load voltage but no flow when the load was applied.

Jon

 

[Keoke]

Dave, With hi on and bulb in circuit put volt meter + on bat input to dipper sw and - lead to high beam out wire. A good sw should show 0 to .3 volts max under load. If sw is open or has high resistance it will show battery voltage or close to it. This is because the gnd at the bulb will cross the filament and move all the way up to the hi side out of sw if the circuit is intact up to the sw. If meter reads more then .3 volt sw has high resistance, how high depends on voltage, 12 volts indicates a complete open sw.
Check wiring between sw and H4 by putting + test lead on sw hi out and - on H4 hi in, voltage drop for full circuit length should not be more then .3 volt under load. All plug in sockets between sw and the first H4 would be prime suspects for a open or hi res connection. A good trick is to fill all plug in sockets exposed to water with clear silicon where the wires enter plugs along with a band of tape where the m/f joint come together.
Note, .3 volt drop is not a good number only a max. number, .1 would be a good number. Use low scale on meter if you have one.

 

[whiterose]

Hello Michael.

You say the 12 volts show on the multimeter both on dip and high. If you have the bulb/bulbs in place and can still connect to the terminals you'll find that there will be 12 volts on the dip so they light. But there cannot be 12 volts on the high beam or else it would light too. So the 12 volts is collapsing with the bulb in place. This can only mean there is a high resistance in the circuit. Can you connect the multimeter to the ground or direct to the neg on the battery then follow the circuit from where it leaves the light switch. Assuming there is 12 volts on that switch when connected to the high beam terminal. Without a wiring diagram its hard to say more.

 

[whiterose]

Testing a circuit like you are doing with no olad on it can produce misleading results.
A bad contact in a switch or relay can send a 12 volt signal along the circuit but all changes when you ask the same circuit to transmit 5 amps for example, then it fails.
Do your tests with a bulb in the socket.
Dave M7040

Fully concur with you here Dave on your comments.