High beams will flash but won't stay on - anyone know how the switch works?

[tech_dog]

I'm trying to figure out why my high beams don't come on when I push the light control switch forward to the locked position. They work when I pull to flash.

If this is TLDR, my actual question is at the bottom.

I'm looking at the dimmer combo switch (84140), which is pressed and released by the movement of the light switch (84110).

After looking at the electrical diagram, I proved the following:

1. rotating the knob turns on parking lights and headlights as it should.
2. flashing the high beams activates the high beams if headlights are on
3. flashing the high beams activates the headlights and the high beams if high beams are off.
4. Clicking the high beams to locked on does nothing, with headlights on or off

The fact that the headlights come on prove that the wire with red dots has +12 and the wire with black dots has a path to ground.
The fact that the brights come on when flashed prove the dimmer combo switch has a path to ground.

If these are both true, it means the wire with yellow dots has a path to ground when flashed, but not when locked on, pointing to the dimmer combo switch not doing what it's supposed to.

( I think HF is Headlight Flasher, HV is High Beam Voltage, HL is Headlight Low Beam. )

The problem is that the dimmer combo switch doesn't look like it could possibly provide a path to ground when it's locked on and fully extended. The image below shows the switch, the metal plunger on the lower right, which is pushed in by the light switch when flashed, fully extended when locked on, and mid-travel when neither. When depressed the spring loaded switch activates the high beams as it should, but it does nothing when it's fully extended.

Question ==>> Can someone confirm if this plunger is supposed to close the HF circuit a the bottom of its travel, the HV circuit at the top of its travel, and is only open in the middle of its travel? Or am I missing something else that's keeping this from working?

Thanks for any help. This has bugged me for most of a decade.

T.

 

[Squash]

Check the relay in the your engine bay.
Mine would work for a while if I pulled it, and re-installed. I finally swapped it out for a new relay and instant gratification.
I have a spare combo switch because that was my first thought. Before thinking of swapping the switch I just plugged it in and conditions were identical, hence the relay.
There are two relays, high beam should be black, and it's companion is brown.

 

[jonheld]

In a USDM 80, all 4 bulbs are fed from the same 1 relay/2 fuses, so if the issue is with the high beams only, the problem is not relay/fuse related.
The highs are a switched ground through the stalk using the same ground for both flash and high beam on.
If flash works but "on" doesn't, the issue must be in the stalk switch.

 

[Malleus]

Common problem. I gave up trying to fix the stalk and replaced it.

 

[tech_dog]

I think I figured this out at midnight or so last night.

While the stalk switch controls parking and headlights, it's only a mechanical influence on the brights, pushing or releasing the plunger switch on the separate dimmer combo switch, which completes the brights circuit to ground.

The three green wires in the image below are for the turn signal, not part of my problem.

The white wire, actually W-B, coming from under them is the path to ground. R-W grounds the headlight relay when the headlights are flashed. R-Y grounds the brights, but it only lights them up if the headlight circuit is already grounded by the stalk switch.

I used a jumper wire to short W-B to R-W and it did indeed ground and activate the main headlight circuit.

I used a jumper wire to short W-B to R-Y and it activated the high beams, but only if the main headlight circuit was already activated by the stalk switch.

I think that these two tests prove that the problem is in the oddly named dimmer combo switch. The plunger switch is closing circuits as expected when fully depressed, but it is not closing the HV to ED connection when it is fully extended.

I still wish I could confirm the expected behavior of the plunger switch on the dimmer combo switch. I'll wait another couple days for more feedback, but I'm on the brink of just buying the part.

 

[Malleus]

 

[tech_dog]

I've got a new Headlamp Dimmer Switch on the way. Original part for 91-95ish was 84140-60160, which is out of production. 84140-26100 is listed as a substitute, still available from US sources.

Does anyone have tips for replacing the terminals in the connector? I looked for a thread on how to get the old terminals out but couldn't find anything.

 

[jonheld]

I've got a new Headlamp Dimmer Switch on the way. Original part for 91-95ish was 84140-60160, which is out of production. 84140-26100 is listed as a substitute, still available from US sources.

Does anyone have tips for replacing the terminals in the connector? I looked for a thread on how to get the old terminals out but couldn't find anything.

If you download the EWD, starting on page 12 it shows you how to replace terminals on various connectors.

 

[tech_dog]

The new Dimmer Combo Switch is here and it solved my issue. I've got properly functioning brights for the first time in a decade.

I've read quite a few posts that seem to confuse the combo switch function with the stalk switch function, so I'll summarize here.

The stalk switch turns on parking lights and main beams, but for brights it's just a mechanical influence on the separate combo switch. As long as the stalk switch is clicking forward and back as it should, it's not contributing to your brights not coming on.

If the main beams come on but you can't flash or sustain brights, your problem may be the dimmer combo switch. It's supposed to be providing a ground for the high beams, but from what I've read in here they tend to go bad as mine did. It seems people may be replacing the stalk when the problem is the dimmer combo.

The original part for the dimmer combo switch for 90 to early 95 is 84140-60160 but it is discontinued. 84140-26100 is a reasonable substitute, with the same function, form, and terminals. The only apparent difference is the length of the pig tails and a brown sleeve instead of dark gray. You could solder in your old pigtails, or trim and re-terminal the new, but it's easy enough to just double up a section and zip tie it in.

The brown sleeve shows the new wiring after installation onto the turn signal switch assembly.

T.

 

[Schnurr22]

This thread was a huge help, thanks for the effort. we are having a low beam issue and worked our way through the obvious stuff like grounds & relays. Thank you for your effort on this repair right down to the individual part. We have a parts 80, we will start with the cleaning the whole assembly and plug in to ensure its viable. If not we will follow your parts lead. Again, thank you very much for your effort on this!!