'88 Headlights acting weird.

[Hoosierman]

I'm not sure if my attachments will go through, they tend to be hit or miss with me. Anywho, looking at the IN connector from the main switch, I don't see any R/Y wires. One that is kinda obscured is the R/W wire. However, on the OUT connector from the dimmer switch to the headlights, there is both the R/Bk and R/Y wires, each of course going out.

Or am I misunderstanding the color codes?

Edit: The gray connector is the IN connector. The OUT happens to be dangling behind it in the photo, so it may seem that the IN connector has the R/Y wire going into it. But just so I clarify: I am reading that the R/Y wire is on one connector, and the R/Bk wire is on the other connector, and I am to jump the two. However in my case, BOTH wires are on the OUT connector.

 

[RobbieD]

To answer your latter Q: I very seriously doubt that I have a lights out warning on this rig, I've never seen one.

I don't think your truck has it; you'd see the display easily either above the mirror or in the console.

I'm not sure if my attachments will go through, they tend to be hit or miss with me. Anywho, looking at the IN connector from the main switch, I don't see any R/Y wires. One that is kinda obscured is the R/W wire. However, on the OUT connector from the dimmer switch to the headlights, there is both the R/Bk and R/Y wires, each of course going out.

Or am I misunderstanding the color codes?

Pictures do help a lot; thanks.

Don't think "in" and "out" connectors. Use the multifunction connectors pinout below; your target wires are on the lower part of C201. You are holding C202 in your picture.

 

[Hoosierman]

I don't think your truck has it; you'd see the display easily either above the mirror or in the console.



Pictures do help a lot; thanks.

Don't think "in" and "out" connectors. Use the multifunction connectors pinout below; your target wires are on the lower part of C201. You are holding C202 in your picture.

View attachment 108086

Noted. I was thinking this but I thought it weird to jump two wires on the same connector- admittedly. So on the C201, yes, there are the R/Bk and R/Y wires. I familiarized myself with those today before leaving for work. I will note that one of those two wires appears to have been removed from the connector that had melted at some point, but still hooks up to the connector fine otherwise with a spade terminal.

That said, if I jump these two and still do not have lows- then should I suspect that against very low odds, the low beams simple went out at the same time?

 

[RobbieD]

Noted. I was thinking this but I thought it weird to jump two wires on the same connector- admittedly. So on the C201, yes, there are the R/Bk and R/Y wires. I familiarized myself with those today before leaving for work. I will note that one of those two wires appears to have been removed from the connector that had melted at some point, but still hooks up to the connector fine otherwise with a spade terminal.

That said, if I jump these two and still do not have lows- then should I suspect that against very low odds, the low beams simple went out at the same time?

If a connector or wire looks melted it's a sign that the wire or the connection to the terminal could be bad.

To test that, stick a straight pin through the plastic insulation of the Red/Black wire an inch or two away from the multifunction switch. Test for voltage with headlights on low beam.

If no voltage, bad switch, terminal or wire at the switch.

If the pin has voltage, move to C120 and probe the terminals on both sides. If no voltage, the wire has an open between the switch and C120.

If Red/Black at C120 has voltage, move to the drivers, then passenger headlight connectors. If you have voltage in both Red/Blacks at these places, then yes, both of your headlights have burnt out low beams.

It's doubtful that you have a grounding problem at the headlights, because the high beams DO work.

 

[Hoosierman]

I

If a connector or wire looks melted it's a sign that the wire or the connection to the terminal could be bad.

To test that, stick a straight pin through the plastic insulation of the Red/Black wire an inch or two away from the multifunction switch. Test for voltage with headlights on low beam.

If no voltage, bad switch, terminal or wire at the switch.

If the pin has voltage, move to C120 and probe the terminals on both sides. If no voltage, the wire has an open between the switch and C120.

If Red/Black at C120 has voltage, move to the drivers, then passenger headlight connectors. If you have voltage in both Red/Blacks at these places, then yes, both of your headlights have burnt out low beams.

It's doubtful that you have a grounding problem at the headlights, because the high beams DO work.

I wonder, would checking the connector with an ohm meter figure the same thing out, more or less?

 

[RobbieD]

Yes and no.

An ohmeter will test the resistance of the section of the circuit (the combined wire, terminals, etc.), say from the dimmer switch connector to a headlight connector but you need both ends disconnected and your meter probes go these two ends. That's OK if the harness is out of the truck on a workbench, but in the vehicle they'll be so far apart that reliable testing would be difficult.

It's much easier to test for voltage, like I described earlier. Start at the beginning, in this case at the dimmer switch C201, with the lights on and work your way down the circuit to the end- start at C201, next at C120, then at the driver headlight, finally at the passenger headlight. Your meter red lead goes to your target wire or terminal, its black lead to the closest good chassis ground. On a good circuit your beginning voltage, say +12.0V, will NOT drop much from start to finish. This is a voltage drop test, and it's much easier, and quicker.

An old-school test light would work just fine to troubleshoot a problem like this. Best advice is, use the wiring diagram to figure out how the circuit works, and then don't overthink things.

 

[RonD]

As shown in the Diagram on previous page, all 3 head light wires are on C201
red/yellow = 12v IN from main light switch
red/black = out to low beams
light green/black = out to high beams

And all 3 at the lower end of C201 in above drawing

Jump it

 

[RobbieD]

Jump it

Jump it good!

When a problem comes along
You can jump it
Because the lights are out too long
You can jump it
When something's going wrong
You can jump it

Now jump it
Into shape
Shape it up
Get straight
Go forward
Move ahead
Try to detect it
It's not too late
To jump it
Jump it good

 

[Hoosierman]

I finally got back to this... Four months later thanks to other things that came up.

So I ran a jumper wire from the dimmer switch itself to the headlights and had power. Something downstream from the switch I'm guessing is shot. However, with that being said, I found a solution that does work. I hooked up a new HD headlight harness from LMC and both lights totally work when they receive battery power directly.

 

[Hoosierman]

I figured I would update this once more.

Over a month later and the headlights are great, couldn't be any happier with the arrangement at all. Unfortunately the low beams stopped working once again, only this time, I found out the culprit almost by accident. I discovered that the ground wire to the firewall was loose so I tightened it (I should have checked that earlier, I knew better, I own two old Jeeps). Tightening, although means all the difference in the world, still did nothing for the lights. However, I dropped my heavy ratchet and suddenly the low beams came on! I appeared to have dropped them on a mess of cables! Whenever the lows don't come on, if I fiddle with it, they will return. I included a picture with the mess in questions circled in blue.

Before I go prying, what is this, C118? I found that the O/BK wire has a significant tear in it, so I'll be getting on that. Chesterton's Fence, I suspect this was taped for a reason...