headlight issue

[cfgioja]

I am working on my 1986 944 turbo and the passenger headlight seems to be working fine. The driver side headlight on the other hand lights up dimmly. I have checked the ground and get full power to it and clean ground.The light switch must work if it turns the passenger to high beam.

I went a little further and unplugged the light from the connector and found that the power only comes through the 1 and 3 connector, even when it is switched to high beams it does not switch to connector 2.


Does this show the light relay to be bad? I am not sure what to do next.

[Vicious]

from your description i would guess bad ground, but if you checked it possibly the filament is bad. when you switch to high the headlights should each have their own ground be sure to check the right ones

[cfgioja]

brand new buld, last one was this way thats what made me change.

When I tested the ground it made no difference on the rail or to the terminal, the voltage was the same.

When I flipped from low to high the wires did not switch to connector 2 it still stayed on the connectors 1 and 3. It is making me wonder if the relay is stuck and is causing a short.

[cfgioja]

How many amps are suppose to be at the headlight? I have only been checking voltage. The other big thing is why is it not switching from high to low beams on that connector?

[HondaDustR]

Does the late electrical system use relays for the headlights? If so, that would be the first place to check. It could also be the light swich. I'm not familiar with the late switch, but the early switch likes to randomly burn up since the early system does not use any relays, and I believe it had separate contacts for each headlight (but common ground contact which was what failed on mine...don't know what they were thinking), meaning it would be possible for only one side to go bad. If the late switch is the same idea, that could be a possibility. It could also be internally corroded wires or a bad ground that cannot pass enough current. If you get good voltage at the connector with the light disconnected but low voltage when it is powering the light, measure further up the circuit until you isolate the source of the voltage drop. Sounds like you'll need to spend some quality time with a circuit diagram and a multimeter.

As far as amps go, P=VI. So with a 55W headlight bulb, plug in your source voltage (different between engine running and not running due to alternator charging) and solve for your expected current. There's most likely a bad connection or wire somewhere that can't pass that amount of current. P=R*I^2 will give you the resistance of the system given your actual amps drawn to give you an idea of how much extra resistance there is causing the problem. For reference, my relay headlight harness I built that pulls straight off the alternator had a voltage drop of only 0.15v between the battery and the bulb connector. Stock wiring before that had a 1.9v drop, but that's with the early system that sends full current through the switch.

[guru944]

cfjioja:

Try putting a simple rectifier diode in series/line of the pin 3 to your ground ($1.29 pack of 2 @ Radio Shack, generic# 1N1004). Sometimes, you can have reverse current in the relay and by adding one, it will provide proper forward bias (Also good for Ground loop, noise issues fix ) and the relay response will improve.

Note: Arrow and bar in schematic diagram points to GND or lower potential (Ring around body of diode ).

[cfgioja]

Did some tinkering and found out that theere is a short between the two lights. I hard wired a seperate ground for the driver light and they work now. Its not a perfect fix but works for now.

Thank you for the inputs