Dim headlight

[J Witt]

The left headlight is dim relative to the right headlight. Measured with a light meter, the left is about 2/3 as bright as the right. This difference is only on the low beam side, the highs are equally bright. The bulbs are the 30/35 watt halogen, 6V

My suspicion is that either there is a high resistance splice somewhere in the harness, or a problem in the switch.

The following things have been checked:

Bulbs swapped side to side, with no difference
separate ground added from the headlight shell to chassis
headlight lenses cleaned inside and out

I haven't been able to check to see if the focus is the same, but I'm measuring right at the lens, so I think that shouldn't make a lot of difference. The sockets are close to the same distance out from the reflector hole.

Anybody know where in the harness the wires would be spliced? Any other things to check?

Thanks,

John

[2manycars]

Try swapping the bulbs to see if it is a problem in the wiring, or a bad bulb.

[Ray64]

My 30 coupe was the same way and it was a poor ground between the bucket ans the light bar

[Patrick L.]

OK, so swapping bulbs made no difference as your post said. Generally the problem would mean a poor ground but the high beam works good, so, I'd suspect a connector issue. If you are using the original style connectors, they have been know to make people come up with some very creative language and to pull ones hair out. Some take the time to fix those connectors, especially the repo's. I don't have the patience and just eliminate them.

[2manycars]

Wow, I better get more sleep so I can reply with some sense.

[Tom Wesenberg]

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Seems you've tried all the logical checks. If anything, the left should be a hair brighter (like .1 lumen) because the feed wire is a bit shorter.

Are both reflectors silver plated?

[J Witt]

Yep, the headlights are, I assume, re pops and are in very nice condition. I didn't mention it before, but these are the '31 single bulb headlights

The wiring harness is the cloth covered repro style and connectors aren't visible. Are they buried in the harness somewhere, or perhaps inside the headlight switch? I haven't had the headlight switch off yet to look at it.

[Kurt in NJ]

originally (at least in my harness both headlight wires come together at the switch)---recently I worked on a car that had a cheap repro harness, the wires had push on terminals, one was corroded, originally both wires are soldered

[Patrick L.]

Originally Posted by J Witt

Yep, the headlights are, I assume, re pops and are in very nice condition. I didn't mention it before, but these are the '31 single bulb headlights

The wiring harness is the cloth covered repro style and connectors aren't visible. Are they buried in the harness somewhere, or perhaps inside the headlight switch? I haven't had the headlight switch off yet to look at it.

OK, I was talking about the connectors at the headlight. But, it seems like there is a poor connection somewhere in that wire from switch to light.

[Mitch//pa]

You can easily tell if it's a ground issue or a power feed problem using a 2.00 basic testlight at the end of the juice where the bulb contacts

[Tom Wesenberg]

You say you jumped the shell to the chassis, but you might want to jump the socket direct.

Is the headlamp visibly dimmer, or are you only going by the meter readings?

[J Witt]

OK, so this morning I took the switch apart and it is the style with spade terminals. I soldered the headlight wires into the terminal crimps and re insulated with new heatshrink, even though the connections looked OK. Also squeezed the terminals down a little to make a firmer connection. However, since the power wires for both sides originate in the same place, the issue must be further downstream, so I'll open the headlights up again and check through those connections. The headlight wires are actually hardwired to the bulb socket and do not have the connector that feeds through the headlight shell. That's partly what makes this situation puzzling as there are no connectors in the line until you get to the bulb itself.

When I installed the bulbs, I bent the socket sides in slightly so there is a firm ground connection to the base of the bulb.

The difference in brightness is visible as well as measurable with the meter. There is about 3500 lumens on the right side and about 3200 on the left side. This can be made to vary some by changing the focus, but not enough to equalize the brightness. Besides, I'll want to set up the focus for the right beam pattern.

I'll get a resistance measurement as well and see if there is some source of high resistance in the left side wire.

I'm running out of ideas and airspeed, so I better get to the end of the runway.

[J Witt]

The end of the runway at last. Mitch and Tom had the answer. I ran a separate ground lead to the bulb socket assembly and that fixed the issue. The picture shows the lead soldered to the socket. The other end fastened to the same screw to the headlight shell as the existing shell to chassis ground.

Since I had all the tools at hand, I went ahead and did the same to the other headlight. Interestingly, they both brightened up a bit and now are the same.

Thanks to all for the suggestions.

John