MTFCA Forum

After installing some new LED headlight bulbs, they adjust to dim but will flicker and readjust to bright. By bringing the lever back a few degrees from the complete setting, they will dim again, but that point is very delicate and must be manually maintained. On bright, they both perform accurately. The switch was new a few years ago and has seldom been used as I rarely drive at night. With the standard bulbs, I never noticed how they projected, as there is hardly enough difference. However, I did reinsert those to see if the problem might be the contacts on the LEDs, but the old bulbs performed the same way. Therefore, the problem seems to be in the switch itself.

On the contact layout in the switch, the bright brass contact joins the dim contact to the battery contact from 11 to 3 o'clock, while the bright contact joins the bright contact to the battery contact from 7 to 3 o'clock. They are significantly separated from each other, and since the contacts fit into brass recesses, there should be no allowance for overshooting a connection, so I can't see why there is this overlapping switch effect. There is a trace of a metallic trail between the recesses, but it's broken with divots that eliminate any continuity.


Where else could the problem lie?

Since the LED & incandescent bulbs both showed flickering - the switch or wiring could be an issue
How are you providing power (what voltage as well) to them when they are at issue: battery only /engine off, engine running power by generator.

The picture of the switch looks okay. When you said the switch was new several years ago, did you mean the entire switch or just the backing plate? Some of the repro backing plates had some reported complaints never isolated to which ones. I do agree that the dimples would interrupt interrupt voltage passing along the trace marks but the question is if the material that the backing plate is made of would prevent an internal carbon tract.

Before cleaning up the traces made by the switch, I would try to do a continuity test along the trace paths (not the real positions) to the BAT position to see if there is an issue there.
To clean up, some WD40 to wash & light sanding. Scraping the traces a bit to remove material shouldn't hurt the switch function.
NO lubricant should be used in the switch or key, especially graphite (a conductor).

Have you tried bending the brass just a little bit to give a little more pressure on the contacts? Also I would suggest checking the sockets. Are they making good contact? I remember one car the center contact on the bulb was not making good contact with the socket. The spring in the socket was weak. Adding a little dab of solder to the bulb helped.
Norm

My 24 Coupe had a questionable headlight socket for a while. It worked fine and then a week or so later not so much. It was a good used original but after a while I bought a new reproduction and it’s still working as it should. No more flickering and then no low beam.

The ground connection from the bulb socket to the headlamp housing can be sketchy and intermittant. Check that out as well.

After opening the switch case, I checked the continuity from the Dim terminal to the battery and right to the battery. There is a good connection between both. Checking Dim to Bright revealed no continuity; however, I inadvertently slipped the volt meter probe down into the screw receptacle and hit the Bright connecting strap (current setting) below and had continuity. Following up, I applied a C-clamp to close the case temporarily, and I was now getting continuity at the face of the terminal as well. I used a piece of tape over the dome heads of the mounting rivets for the strip for a further check, and there was no continuity then. So I ground the heads of those rivets flatter with a Dremel, and that solved the problem. The same thing occurred with the switch at dim, and the same remedy helped.

The switch had been replaced a few years back and not really used as I don't drive it at night, therefore I never paid attention to how the lights were working. One thing I did during restoration was to run a dedicated ground wire to every light fixture on a tip that prevents flickering and cutout lights. I guess there still could be poor contact between the light socket and the grounded shell, though, and I'll get the 12 ga. brass brush out and scuff that clean.

Thanks for all the advice.

Don, my auto electrician son always solders a ground wire from the bulb socket to one of the rivet heads holding the light bucket to the mounting stem to ensure there is contact between the two rather than relying on casual contact between them as installed.

Allan from down under.