Headlights stay ON

[loungin112]

Could a faulty or melted relay be the source of the malfunction?

[PMCS Rally]

Yes, Low Beam stays ON even the light switch connector is unplugged.

Relay was the first one I suspected. I opened the JIDECO Relay 25230-89915 which was very clean and contacts were good.

I thought +12V was always at headlight and switch was controlling grounding.

[510rob]

Yes, Low Beam stays ON even the light switch connector is unplugged.

Then you have a wiring error somewhere. I would suggest pulling the headlight fuses to 'half-split' the system for the next round of troubleshooting.

Relay was the first one I suspected. I opened the JIDECO Relay 25230-89915 which was very clean and contacts were good.

If you refer to the drawing I provided you, you will see that the relay only controls which electrical path is completed to ground; either the high-beam path, or the low-beam path ---> the voltage applied to the bulbs is switched by the headlight switch. It is a circuit layout that has caused a lot of people to scratch their heads over the years, but it works acceptably well when all of the pieces of the puzzle are put into their right places.

I thought +12V was always at headlight and switch was controlling grounding.

No, the headlight switch controls whether or not positive power is applied to the headlights. Again, the relay controls which electrical path is completed to ground.

[PMCS Rally]

By some reason I believed headlight plugs are always HOT so I was focusing on grounding side.

Inside of JIDECO relay was exactly as shown in your diagram sketch.

I am going to trace HOT side wiring now.

Thanks.

[510rob]

Apparently in your case the headlight plugs ARE always hot, which has probably been throwing you off.

The nodes in the drawing are taps in the OEM wiring harness where the factory spliced in a second tap from a run.

Unplug the headlights, unplug the headlight switch, pull out two headlight fuses (there isn't much else in the circuit besides wire junctions). With that in mind, just methodically go from point to point and see where voltage is getting into the circuit. My guess is that you'll find some non-OEM wire cruelty wrapped up somewhere in the harness with electrical tape...

[James]

Non-OEM wire cruelty......it exists more than we want to believe.

[PMCS Rally]

OK, I will go over the wiring section by section.

I am not worrying about modified wiring very much since this was one-owner granny car and I inspected the original wiring harness very carefully before I started restoration. Only thing I did was repairing worn out wires and corroded connectors and kept as as original as possible. The only wiring modification I had to do was converting 3-speed auto to 4-speed manual. I hope this has nothing to do with.

Thanks,

[PMCS Rally]

You were right and I was wrong.

After following all wires I noticed that Red/Yellow wire from Light Switch was not connected to the Fuse Box. I looked closely and noticed that the box was not the right one and does not have Red/Yellow connection. I will replace the fuse box but for now I will connect it to the power with single fuse.

Assumption is a mother of....

Thank you all for advice.

[510rob]

I'm happy to hear you found a problem that lines up with all of the head scratching symptoms. Now it should be a reasonably simple fix.

[PMCS Rally]

Thank you for all your advice.

Just a follow up, I finally realized that there are two types of fuse boxes. Most of us have one with two wires (White and Black/White) coming out from the box. Mine needs a box with three wires (White, Black/White, and Red/Yellow) from the box. Red/Yellow supply power to Right/Left headlight fuses. Right now these two fuses get constant power from White wire. That kept my low beam ON all the time. I think these fuse boxes are NLA so I will modify wiring in the box.

Thanks again.

[yenpit]

I might have a good USED fuse box!

Did you buy a bunch of parts from me years ago? I've been in Denver 8 years, was in Holland & Kalamazoo MI before that!

TJ

[yenpit]

I do have a really clean USED fusebox!

PM sent!

TJ

[icehouse]

Thank you for all your advice.

Just a follow up, I finally realized that there are two types of fuse boxes. Most of us have one with two wires (White and Black/White) coming out from the box. Mine needs a box with three wires (White, Black/White, and Red/Yellow) from the box. Red/Yellow supply power to Right/Left headlight fuses. Right now these two fuses get constant power from White wire. That kept my low beam ON all the time. I think these fuse boxes are NLA so I will modify wiring in the box.

Thanks again.

Dude you can modify the box. If I remember right there are screws for the wires that are different and you can swap things around.

[PMCS Rally]

Yes, it is doable but all wire terminals are riveted down (no screws) on bus bar through fuse holder and I need to cut the bus bar to separate power supply source. I really do not want to modify the original wiring but my plan B is bypassing the fuse box and make a light fuse circuit.