Bricky headlight puzzler

[RenoHuskerDu]

My son's 89 has an odd headlight issue. It has a new dimmer foot pedal. The multiconnector on back of the headlight switch in the dash was somewhat melted so he put in one from a 90 parts truck. The switch itself looks recent.

The symptom is that his highs and lows alternate left and right. The problem was probably there all along but became apparent when he installed LED bulbs. We took those out for now, not wanting to risk them, and have the halogens back in there.

Step on the dimmer, and one bulb gets brighter while the other dims. Step on the pedal again, and it reverses sides. Both plugs on the headlight bulbs have 12v at the same places for High and Low.

It's a puzzler. In the past, strange wiring issues such as this have boiled down to a bad ground. I told him that the headlight switch itself is a weak link. I've had to replace two already on other Bully/Bricky trucks. Perhaps three toggle switches and a variable rheostat for the dash lighting on a fab'd panel could nicely replace the stock headlight switch on the dash?

Here is how both plugs are wired at the bulbs. My first suspicion was a polarity issue. Is this the correct polarity for a Bricky?

[85lebaront2]

I will have to look at Darth's headlight plugs and report back to you. Do check the ground resistance as the grounds could be an issue.

[RenoHuskerDu]

I will have to look at Darth's headlight plugs and report back to you. Do check the ground resistance as the grounds could be an issue.

We'll check grounds tonight after work, to be sure no more than 5 ohms to the negative post.

Thank you

[Gary Lewis]

We'll check grounds tonight after work, to be sure no more than 5 ohms to the negative post.

Thank you

You can’t really ohm out grounds with a standard DVM. Or, I should say you can but won’t get good results. That’s because a standard DVM uses a really small current to test, and even a bad ground can sometimes pass small currents.

The best way is to check for a voltage drop. Put your DVM in voltage mode and test from the negative terminal of the load to the battery’s negative terminal with the light turned on. There should be very little voltage drop.

[RenoHuskerDu]

You can’t really ohm out grounds with a standard DVM. Or, I should say you can but won’t get good results. That’s because a standard DVM uses a really small current to test, and even a bad ground can sometimes pass small currents.

The best way is to check for a voltage drop. Put your DVM in voltage mode and test from the negative terminal of the load to the battery’s negative terminal with the light turned on. There should be very little voltage drop.

My old professional Fluke DMM hangs its head in shame at your revealed truth.

Truth is hard, as they say, and I was about to make that mistake. Thank you.

Voltage drop is what's important, and it also measures insufficient wire gauge, oxidized wires, or other factors. I suspect that his main headlight feed is oxidized at the dash switch, where the multiplug had melted somewhat. He taped it over, but tonight I will have him expose it and take a close look. In the past I've managed to scrape off oxidation on copper strands with a wire brush - tedious - then use solder to re-establish a clean connection. That is if there is not enough spare wire to simply cut off the burnt section.

 

[Gary Lewis]

My old professional Fluke DMM hangs its head in shame at your revealed truth.

Truth is hard, as they say, and I was about to make that mistake. Thank you.

Voltage drop is what's important, and it also measures insufficient wire gauge, oxidized wires, or other factors. I suspect that his main headlight feed is oxidized at the dash switch, where the multiplug had melted somewhat. He taped it over, but tonight I will have him expose it and take a close look. In the past I've managed to scrape off oxidation on copper strands with a wire brush - tedious - then use solder to re-establish a clean connection. That is if there is not enough spare wire to simply cut off the burnt section.

We actually have a page on this: Documentation/Electrical/Voltage Drop Testing. And it finds all sorts of problems, like you said, including cables that look good on the outside but have bad connections between the wire and the terminal.

But if the switch and/or wire going to it is bad that may be the problem.

[85lebaront2]

We actually have a page on this: Documentation/Electrical/Voltage Drop Testing. And it finds all sorts of problems, like you said, including cables that look good on the outside but have bad connections between the wire and the terminal.

But if the switch and/or wire going to it is bad that may be the problem.

I have run into headlight bulbs that appear identical but the L H and G pins are in different locations. Just for the heck of it swap the bulbs side to side, if the problem follows the bulb, check the numbers on them. If it remains the same, then dig into the wiring.

[grumpin]

I have run into headlight bulbs that appear identical but the L H and G pins are in different locations. Just for the heck of it swap the bulbs side to side, if the problem follows the bulb, check the numbers on them. If it remains the same, then dig into the wiring.

Good thinking Bill, I remember seeing or hearing about that.

 

[RenoHuskerDu]

I have run into headlight bulbs that appear identical but the L H and G pins are in different locations. Just for the heck of it swap the bulbs side to side, if the problem follows the bulb, check the numbers on them. If it remains the same, then dig into the wiring.

I suspect that we may have had that issue, because he grabbed two old halogen bulbs out of a box for testing. We put LEDs in pretty much everything, now that we found a brand with a good pattern on the road and longevity. Ersatz bulbs from our fleet may have caused the odd symptoms in my OP.

But when we tested for voltage drop tonight, we found a bigger problem. When a halogen bulb is running on the driver side, the voltage supplied to the passenger side socket high beam drops to 7v. I also noted that 0.2v leaks in from the parking lights into the low beam circuit on that side.

At this point, given the age of the truck, I'm going to teach him how to put his headlights on battery-direct relays so that the (apparently functional) driver side headlight wires only trigger the relays. Should be a good teachable moment for the young man. And we'll use new headlight plugs and all-new 14g wires in split loom, so he could also use that to run an LED light bar etc. As young men do these days.

Gary you and I are of the pre-halogen age when DOT sealed beam headlights were dismally dim and that's all anybody had. I was 16 when I first discovered Cibie and Marchal replacement lamps with - gasp - halogen H4 or H1 bulbs, in non-DOT non-sealed beam EU lenses. They were as much of an improvement as LEDs are today. But they sucked down the power, so I always installed battery-direct relays. On one Volvo 244 with quad lamps I wound up running hi-watt H4s in all four for a retina-sizzling total of 480 watts. That car had battery-direct relays fed by the stock Volvo relays, lol.

I once wangled my way out of a speeding ticket by convincing the cop to write me up for illegal lights instead, a fix-it ticket that was dismissed merely by showing they had been replaced with sealed beams. Until I got home.

[Gary Lewis]

I have run into headlight bulbs that appear identical but the L H and G pins are in different locations. Just for the heck of it swap the bulbs side to side, if the problem follows the bulb, check the numbers on them. If it remains the same, then dig into the wiring.

I suspect that we may have had that issue, because he grabbed two old halogen bulbs out of a box for testing. We put LEDs in pretty much everything, now that we found a brand with a good pattern on the road and longevity. Ersatz bulbs from our fleet may have caused the odd symptoms in my OP.

But when we tested for voltage drop tonight, we found a bigger problem. When a halogen bulb is running on the driver side, the voltage supplied to the passenger side socket high beam drops to 7v. I also noted that 0.2v leaks in from the parking lights into the low beam circuit on that side.

At this point, given the age of the truck, I'm going to teach him how to put his headlights on battery-direct relays so that the (apparently functional) driver side headlight wires only trigger the relays. Should be a good teachable moment for the young man. And we'll use new headlight plugs and all-new 14g wires in split loom, so he could also use that to run an LED light bar etc. As young men do these days.

Gary you and I are of the pre-halogen age when DOT sealed beam headlights were dismally dim and that's all anybody had. I was 16 when I first discovered Cibie and Marchal replacement lamps with - gasp - halogen H4 or H1 bulbs, in non-DOT non-sealed beam EU lenses. They were as much of an improvement as LEDs are today. But they sucked down the power, so I always installed battery-direct relays. On one Volvo 244 with quad lamps I wound up running hi-watt H4s in all four for a retina-sizzling total of 480 watts. That car had battery-direct relays fed by the stock Volvo relays, lol.

I once wangled my way out of a speeding ticket by convincing the cop to write me up for illegal lights instead, a fix-it ticket that was dismissed merely by showing they had been replaced with sealed beams. Until I got home.

I think you are right, it is time for relays.

As for the H1 and H4 bulbs, my CB750K1 got the first such. And I carried a spare bulb, which gave me a warm, fuzzy feeling. Moved that setup over to the Yamaha XS11 in '78, and have been a fan ever since.