The night the lights went out on my cutlass ha

69hurstolds

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Jan 2, 2006
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I'm going to rule out the grounds as a very unlikely problem source. There are two grounds, one on each side for the headlamps. So in theory, it would be very unlikely both went out at the same time.

The switch to the headlights has a built in circuit breaker which may be hosing up. Unlikely, but a new switch MIGHT help. But here's the rub. You have to have the headlamp switch ON to get the high beam light. Meaning the switch and circuit breaker needs to work.

While the blue light is on indicating high beams, click the high beams and see if the light goes off. It should. Meaning the dimmer switch may be working correctly. If it's NOT, it might be the dimmer switch itself.

There's a rod going down to the dimmer switch along the left side of the column (when sitting in driver seat). The switch itself is located right behind where the left side bolt holds the column to the dash. The rod might fall out if you remove the switch, so if you change it out, just tape it to the column. 2 small screw heads (7 or 8 mm I think?) like sheet metal screws hold it on to the ignition switch that sits on top of the column. 7838234 is the GM number for the switch. Standard Motor Products has it as DS79. There are likely others. They are not too pricey. But a bit of a PITA to replace just because of where it is located.

Here's what the switch looks like when viewed from the left side of the column. OEM is similar in appearance, but hooks up the same way. The rod from the dimmer actuator inside the column fits in the RH end of the white plastic shown below.

SMP-DS79_HN.jpg


There is a C100 connection for the headlights coming out of the dimmer switch that's located on the connectors coming out of the firewall under the wiper motor. TOUGH to get to. Unlikely it's this connector.

There's a yellow wire coming from the headlamp switch that goes to the dimmer switch on the column. The other two prongs have tan (low beam) and green (high beam). If you pull the plug on the dimmer switch and use a jumper wire to connect the yellow to the tan and then the green, you can test to see if your headlamp dash switch is working, and if the dimmer switch is bad at the same time. Once you put the jumper from the yellow wire connection to either tan or green, then turn the headlamp switch on briefly and see if the headlamps come on. If they do, it's the dimmer switch. If they don't, it's likely the headlamp switch or a bad section of wiring from the headlight switch all the way to the lamps somewhere. The odd part is that when the high beam switch is on, then the high beam indicator on the dash lights up. This is before that firewall connection point C100.

I'm not an electrician, but you have to get power to the lamps and this dimmer switch is a key component. Without it, you won't have low or high beams.
 
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melloelky

Comic Book Super Hero
Oct 22, 2017
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mass
hopefully she gets to the bottom of it and reports back as this is a weird one and it could help someone down the road..
 
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69hurstolds

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Jan 2, 2006
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It is weird. I'm not an electrical wizard, but I can follow a wiring diagram fairly well.

The strange thing I can't get my head wrapped around is that the dimmer switch sends power to the high-beam indicator when you click it to high-beam at the same time it's sending power to the high-beam circuit to power up the high-beam lights. dafuq????
 
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69hurstolds

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Jan 2, 2006
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The question needs to be asked...when does the high beam indicator come on? With the parking lamps and headlamps or is it out until the headlight switch is activated? It should only come on when the headlight switch comes on. The circuit breaker in the headlamp switch appears only to be on the headlamp circuit power coming in, so if it was the switch, where would the high beam indicator get power? I guess you could remove the dimmer switch wire plug, measure the voltage from the yellow wire with headlamp on and off and see if the switch is working. Kind of a PITA to change the switch if it doesn't need it.

Sorry about the pic, it's a bit grainy due to the lack of lighting when I took it, but you can still read it.

85 Oldsmobile Headlight Dimmer Switch Diagram.JPG
 

PVDave

Not-quite-so-new-guy
Oct 28, 2021
8
3
Arvada, CO
It is weird. I'm not an electrical wizard, but I can follow a wiring diagram fairly well.

The strange thing I can't get my head wrapped around is that the dimmer switch sends power to the high-beam indicator when you click it to high-beam at the same time it's sending power to the high-beam circuit to power up the high-beam lights. dafuq????
The high beam indicator is just another bulb in the high beam circuit. The difference in bulb size makes no never mind- The circuit feeds the indicator 12 volts, and it lights up along with the high beams.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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The high beam indicator is just another bulb in the high beam circuit. The difference in bulb size makes no never mind- The circuit feeds the indicator 12 volts, and it lights up along with the high beams.
Yeah, I just explained that. It's that (assuming all the headlights aren't burnt out) the high-beam indicator gets its power from the same switch as the headlights. So the dilemma is the headlights aren't working, but the high beam indicator is lit? Just how is that happening? That's the question that needs answering.
 

PVDave

Not-quite-so-new-guy
Oct 28, 2021
8
3
Arvada, CO
Yeah, I just explained that. It's that (assuming all the headlights aren't burnt out) the high-beam indicator gets its power from the same switch as the headlights. So the dilemma is the headlights aren't working, but the high beam indicator is lit? Just how is that happening? That's the question that needs answering.
Based on the schematic you posted, I'd say the issue is Connector C100, Terminal D2- Power on the cabin side but a corroded connection keeps it from passing through to the engine bay. The wiring to the high beam indicator runs on the cabin side of the circuit.
 

69hurstolds

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Jan 2, 2006
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C100 connectors are unlikely but cannot be ruled out completely. They simply don't fall off, unless they weren't put on correctly or were tinkered with previously. It's possible, although highly unlikely it's the D2/E2 connector (bottom center plug on the C100 firewall port) that resides under the wiper motor and is nicely tucked behind the inner fender liner. PITA to get to. It's an unlikely subject, but needs to be pinned on the troubleshooting board. In any case, I'd deal with getting to that one last since it's easier to do the other checks.

This is why I mentioned to use the dimmer switch plug and jumper out the tan and green wires with the yellow one, one at a time to test, along with using the headlamp switch to see if there's something going on without the dimmer switch in the circuit. A bad dimmer switch could be causing some issues as well. Test it all. Don't leave anything to chance.

The question of whether the bright light indicator ever goes off when the dimmer is cycled hasn't been answered. If it does, and the jumper wire bypassing the dimmer switch trick doesn't net anything positive, then the C100 connection needs checking at bare minimum. Hopefully there's not a break in the wiring past that point either. If the high beam indicator stays on all the time, it could be something with the instrument panel circuit film as the wiring doesn't technically go to the indicator bulb.

If the C100 plugs are tight, you'll need to check the wiring all the way to the headlights. If anyone's worked on the car and potentially damaged the wiring, that also can cause issues.

That's all I got and I ain't gots no more. Somebody else can have at this one.
 
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Heather b

Not-quite-so-new-guy
Thread starter
Nov 23, 2021
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You guys are the best. Currently waiting on parts to go ahead and replace headlights, headlight switch and dimmer switch. None were that expensive and she has sat for a while so I figured if I’m doing one do them all. She’s going to the shop for a good once over on wiring and hoses and the such (somethings I just am not ready to tackle alone) so I’ll get back to you on that. To answer the question , blue indicator on dash comes on when I turn the headlight switch on. I can click the rod that turns on/off brights and it doesn’t change the blue indicator being on. Simply said, if the headlight switch is on so is the blue light. I agree, dafuq? Lol. Stay tuned for updates as hopefully they’ll be done soon bc not driving her around is killing me. Starting a new question thread re door locks/linkage if anyone wants to join for more “fun” there. Hahah. Thank you again!!
 
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