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flyjetguy 03-07-2018 08:07 PM

‘00 SL1 hazards/signals all OK until headlights on, then nothing!
Searched the tech threads and haven’t seen this one.

Recently replaced the flasher bulbs (3157) with LED bulbs. The side marker flasher mod was done years ago.

Now of course I get the hyper flash with the hazards and turn signals. I like/need the hyper flash in the road warrior Orlando street environment so I have no problem with that.

I also recently noticed one license plate light was out when I replaced them with LED. After a little sleuthing with the multimeter, found a bad ground wire to one light bulb mount. I connected the ground wire from the working bulb mount to the inop mount and works fine now.

So immediately after the signal bulbs were installed and op checked good signaling and with hazards on, everything STOPS working (no relay clicking no flasher illumination at all) ONLY when the headlights are turned on.

Turn them off and everything works again! :xeye:


TomM96 03-08-2018 01:16 AM

Re: ‘00 SL1 hazards/signals all OK until headlights on, then nothing!
undigested comment ~

The resistance of cold incandescent bulbs is very low, so when the flasher turns them on, the current is maximum.

When the filament heats up, the resistance rises significantly, dropping the current flow down a lot.

The LED bulbs never draw as much power as the hot incandescent... and Much less than the incandescent does at 'turn on' (initial inrush).

.... So , possibly the low power drawn by the LEDs is not sufficient to 'prime' the timing circuit (or, Heater) in the Hazard/flasher control unit.
I think sometimes LEDs work on brake circuits, but not signals.

That issue only arises when headlamps on , suggests maybe the headlamps are saturating the power available from a circuit common with the signals.

>>> there's nothing notably consistent in my comments... Sorry !

fdryer 03-08-2018 08:38 PM

Re: ‘00 SL1 hazards/signals all OK until headlights on, then nothing!
Did you check for blown fuses?

flyjetguy 03-09-2018 12:34 PM

Re: ‘00 SL1 hazards/signals all OK until headlights on, then nothing!
Well would any blown fuse/relay heal itself and work properly during the day time with the headlight switch off?

Not trying to be a smart donkey just trying to eliminate things based on what works when. Several days after the bulb changes, the turn signals and hazards [U]all work beautifully [U][/U][/U]with the headlights turned off. The daytime running lights don’t affect the signals/hazards.

However, when the headlight switch on the stalk is in the “parking lights on” or “headlights on” position, nothing. No clicking from the relay, no turn signals, no hazards. I’m looking at the electrical chart in my little repair manual but not seeing where the magic is stopping.

I’ll replace one or more LED flashers with the old incandescent bulbs. If your theory about the current draw being so low the relay just isn’t participating, that should convince it to come out and play.

I will also disconnect the headlight bulb assemblies, turn the headlight switch on, then check. That should settle whether it is current draw related or just a simple switch/ground path.

fetchitfido 03-09-2018 02:38 PM

Re: ‘00 SL1 hazards/signals all OK until headlights on, then nothing!
It may not be the lack of current draw, it may be the fact that LED's are diodes and the headlight switch might not be able to handle them. Power flows through "not diodes" any which way it feels like, with diodes it only goes 1 direction and the way the wiring is setup (haven't checked) could require the non-diode functionality.

Further clarification: Is the problem only when you turn on the headlights or is it also a problem when you turn on the parking lights?

toggenburg 03-09-2018 04:57 PM

Re: ‘00 SL1 hazards/signals all OK until headlights on, then nothing!
"checked good signaling [U]and[/U] with hazards on".

fdryer 03-09-2018 06:06 PM

Re: ‘00 SL1 hazards/signals all OK until headlights on, then nothing!
I ask the basic questions first to eliminate the not so obvious when very strange symptoms are presented, especially after mods. The service manual often mentions any electrical modifications may damage GM electrical/electronic circuits. Replacing incandescent lamps with leds shouldn't hurt but there are circuits where they may interfere with circuit operation. Dome and trunk lighting is a no-brainer (I added two dome style leds to my trunk circuit to have more light). Its well known that led signal lights cause faster blinking due to the lower current used in leds that create the fast blinking cycle - the conventional flasher module using a thermal switch relies on current to heat and operate the flasher module. Diodes can create unusual problems in some circuits that don't have them like the turn signals. Side marker and brake lights shouldn't cause problems but then again the body control module controls lighting and as an electronic module, it may be affected by leds. The dome and trunk lights are also bcm controlled. To have a full view of this problem, a full set of wiring drawings is needed to see if there's something obvious. I cannot explain why your mods worked one day then fails. Disconnecting headlights may be going about troubleshooting incorrectly when the mods (leds) are the reason for the issues. Simply going back to incandescents should solve the problem to verify the problem exists with leds and not a wiring problem.

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