My Astro headlights are acting up. The left side high beam works normally, but the other 3 lights won't go to full brightness. Also, when I'm on low beams none of the three go off, they just shine dimly. I know one headlight is wired to a daytime running light circuit somehow, so I suspect the other three may be back-feeding somehow, or grounding poorly through the DRL circuit. When I pull the DRL relay they behave the same way, just need to turn the headlight switch to "on" first. The DRL function is gone with no relay, as expected. Any insights or experience within the hive with this issue? I have a new turn indicator/hi-lo switch assembly that I can change out. I've checked the voltage at the headlights and get 12 volts, or a little more. I've remove and cleaned several grounds under the hood.Is there anything else?
Have you changed any small bulbs recently?
I used to have a rabbit. I wrongly changed a rear bulb with a single filament bulb that should have been a double filament. It drove me nuts trying to understand why every time I hit the brakes, the dashboard lights would come on as well as the front amber lights would eliminate. Also, I was unaware that this was causing my brake lights to be permanently on.
No recent bulb changes, John , but that's something new to learn.
Are all rear bulbs and any side marker bulbs working as expected?
In reply to iceracer:
It appears that the lighting circuit is switched on the ground side of the lights. I can remove the fuse for the right side headlights and they remain on, dim but on.The turn signal stalk and the hi-lo switch are on the ground side , so I suspect the switch may be the culprit, but is also the hardest thing to change. I'm tracing the ground circuit now, but that's slow going under the hood of an Astro.
In reply to John Welsh :
Yes, everything else behaves normally, it's just the three headlights that aren't. The DRL relay is good, I have a brand new column switch to put in, the wiring around the on/off switch looks good (it can overheat in some GM trucks) and I'm still trying top figure out where the headlight diode is located in this beast. If the column switch doesn't fix it, I'll try the diode next, I guess.
Replace the bulbs that are not working...
If they are seeing 12v at the socket when they are supposed to then it is unlikely a ground or other fault.
In reply to Robbie:
I've got spare bulbs, so that will be easy to try....BUT, the lights are staying on dimly even when they're not supposed to be on. The right side high beam remains on ,even on low beam. It looks like voltage is leaking to ground even when the grounding switch is not. Even that doesn't explain how it stays on with the fuse pulled.
And the problem hasn't changed with a new hi-lo stalk, so it lies somewhere else. This is the reason I hate electrical gremlins.
If you have internal shorts in the bulb, all sorts of weird stuff can happen.
That could easily explain the voltage getting through even when a switch is off. Most bulbs have two circuits through them, and if one circuit is mixing with the other in the bulb...
All four headlight bulbs are single filament bulbs. Each is connected to two wires. I'll have to pull the right side fuse and see how much voltage is getting to those bulbs. I did replace two of the four bulbs without success. I'll have to go buy more, just to be sure.
EvanR wrote:
iceracer wrote:
Grounds !
QFT.
I'll see if there's an easy way to run new ground wires to the three offending lights. I'd rather not start splicing into the headlight plugs just yet.
Hal
UltraDork
4/5/17 6:20 p.m.
EDIT: If the lights are ground switched the problem is not a lack of ground but the presence of an unexpected ground.
If the lights are switched on the ground side, electrical flow would be: Battery + -> Light -> Switch -> Ground. If the lights are staying on when the switch is off something is creating a ground in the wiring between the light and the switch.
Pull the connector at the light and determine which is the ground side. Use a multimeter to check continuity between the connector ground and any ground point. If you have continuity with the switch off, try disconnecting the switch and test again. If you still have continuity the problem is in the wiring between the ground side of the light and the switch.
If the vehicle has DRL, there is probably a tap off the Light -> Switch wire that runs thru the DRL relay and a resistor. So pull the DRL relay and test again. That should narrow down the wiring that you need to check for a short to ground.
In reply to Hal:
I'll try that next. According to a wiring schematic I found, the lights sre switched on the ground side by the column stalk, then it flows through the DRL relay to ground. I wonder if pulling the relay will cut the path to ground completely? There is an alternate ground path through a diode and then back to the DRL relay again. This circuit bypasses the dimmer switch to operate the running lights. Somehow there's voltage getting to the lights unintentionally. If I pull the fuse to the right side lights they'll still be on , but dim. There's got to be voltage feeding through the ground circuit. I've unplugged each bulb, one at a time and recorded how things behave. I'll get the meter out and do as you've suggested and then meter again with various bulbs removed. If pulling the DRL relay kills everything I think I'll try and find the wire between it and the dimmer switch. If I ground that wire temporarily, it might show which part of the harness there's a fault in.
The low beam ground circuit runs back through the dimmer switch, then to the DRL relay ,then to ground. It also splits and bypasses the dimmer switch and flows through a diode before going to the DRL relay, and on to ground. I don't understand the need for the diode, or the effect it may have if it's failed.
Edit: I guess the diode is there to reduce voltage and the headlights burn less bright on DRL.
Yes, i seem to remember a lot of GMs DRLs run at 75%
Diode is a one way switch.
Fixed, but it wasn't a grounding issue at all. I removed the battery in preparation for rewiring all the right side lighting. The lighting harness happens to pass right by the battery, which is a very tight fit in an Astro, and one of the four wires in the harness was broken. The van had died on my son a couple of weeks ago, alternator was dead, so he went to Autozone and had them put in a new battery to get home. I assume the installer broke the wire while fitting the battery. It was the power wire to the right side, and not a ground issue at all. After I fixed the wire I pulled the fuse for the right side and you get three headlights running very dim with no fuse on one side. It took me two days to trouble shoot and ten minutes to fix.
