w124 Headlamp Bulb Change Blows #3 Fuse

[darkman]

I changed my left headlamp bulb. Everything in front seems to work perfectly.
Problem is that when I turn on the lights it blows the #3 fuse (rt tail light,
instrument/switch lighting, headlight cleaning unit, license plate light).

Anyone have any ideas on what I did wrong?

Thanks.

[Jeremy5848]

You may have pulled loose (and grounded) the hot lead to the parking light or the side marker light on that side. Take it all apart again and look for dangling wires.

[darkman]

Thanks Jeremy. I took the unit apart and retraced my steps. I didn't see
anything loose. I dug out all the wiring and fuse manuals. Even though I'm
clueless when it comes to electronics, I'm going to try to see what I can
come up with.

My first thought is to disconnect the wiper washers and see what happens
when they're disconnected. I remember having trouble with that plug the
first time around. Maybe I damaged something in the motor... or twisted a
wire or something.

I've burned up about 8 fuses so far and just went out and bought 10 more.
Now all I have to do is work around the rain we're having. If you have any more
suggestions-- I welcome them.

Thanks again.

[darkman]

Okay...
I've been trying for several days to find this short and I just can't figure this
one out. I tested fuses against every headlight component-- trying to apply
process of elimination. The #3 fuse still blows with all the components out.

When I looked at the ETM, the diagram doesn't exactly match-- the ground
screw that's shown on the right is, instead, on the left. The ETM shows a
bundle of wires running from the ground to some kind of plugin connection.
I can't find that at all.

What I see instead is two bundles of wires attached to the ground screw--
one bundle is visible in attached-image-3. I don't see anything unusual
in the wires or connectors.

Do I need to be checking the individual wires inside, or should I be looking
somewhere else?

attached images:
1 ETM diagram
2 what I actually see
3 closeup of wires from ground

Thanks for any suggestions.

[Jeremy5848]

I've noticed that if you look closely and thoroughly (as you have obviously done), the manuals don't always match what's in the car. It also depends on which manual you have. I see that on my own '87 from time to time. You have to live with it, unfortunately.

Your ground point W9 is in my factory Electrical Troubleshooting Manual (ETM) located at the "lower left front of engine compartment." There is also a ground point W2 which is located at the "lower right front of engine compartment." Make sure you're not confusing them.

W9 grounds the left headlamp and W2 grounds the right headlamp. The "Ground Distribution" page of ETM shows a total of five (5) items grounded at W9:
1) K2 Headlamp Washer Relay
2) M6/2 Left headlamp washer motor
3) S32 Refrigerant high pressure switch
4) M4 Aux fan
5) E1 Left headlamp
My car has only three (3) wires at this point, perhaps in part because I have removed the headlight wiper assemblies when I installed Euro headlamps.

W2 has seven items grounded including the right headlamp and its washer motor, the horns, both washer pumps, and more. I cannot see W2 because the air cleaner is in the way.

My ETM shows that Fuse 3 supplies lamps (park/side marker/license plate), the instrument cluster and center console illumination, and both headlamp wiper-washers.

One problem I had some time ago involved an electronic relay, N40, the Instrument Illumination Control Unit. Located behind the instrument cluster, N40 is in effect an "amplifier," allowing the rheostat (dimmer) in the cluster to handle many more lamps than it would otherwise be able to do. If it shorts internally, it will blow fuse 3; you can remove every lamp in the car and N40, if bad, will still blow fuse 3.

Here's a test that might work and will be easier than removing the cluster: turn the dimmer rheostat all the way down to "off" and replace fuse 3. Now turn up the dimmer rheostat and see if fuse 3 blows. If it does, the problem is somewhere in the instrument/cluster/console area and I would check N40 first. Remove the instrument cluster and then remove the plug from N40 (easier than removing N40 itself, the plug is where you can get at it). Does the fuse-blowing stop? If so, N40 is bad.

Jeremy

[scottmcphee]

If all you did was change one bulb, then something you touched has caused something on the low beam hot circuit to short itself to ground and stay there. With the car off and everything, unplug the bulb. Test for continuity between the all the bulb socket pins (3 of them) and ground. Only one of them should buzz or light or show near zero ohms, the proper ground pin. If you got ground on the low beam too, chase it backwards.

If that's not it maybe the bulb you put in is defective. Maybe it has a short to ground on its low beam filament. Swap your right bulb into your left side. Leave right empty, and try the lights again.

[darkman]

Thanks guys, for the quick response. I'm going back out to work
on this now while there's still some light.

I think the W9 is the right one because the fuse blows the
console lights and right tail and side marker. There are 5 wires
coming from the ground, so I think we're referring to the same one.

I'm going out to check the rheostat-- and thanks for describing WTH that
is .

@scottmcphee
I had already questioned whether it was the bulb. Went back to the store
to make sure it was the right type. I didn't try swapping the left and right
bulbs. I was worried about repeating whatever I did wrong. I did try it with
no bulb at all and the 3 fuse blew anyway.

After I check the rheostat, I'm going to try to do the tests you suggested.
I have a multimeter that I've never used. I've been going over the instruction
manual and reading related posts here on the forum. This electrical stuff is
something I'm unfamiliar with so it'll be on-the-job-training for me on this one.

Thanks again. I'll report back

[JimSmith]

You seem to be saying merely turning the light switch to the position that turns the headlights on blows the fuse. Is this the case with the connectors unplugged (not just the lamps removed)? I presume this is a USA car with USA DOT approved lights (sealed beams).

I have found on some replacement bulbs and especially when I installed Euro headlights from a particular supplier that the blades on the bulb could cause such problems. This would be true for old connectors as well - especially if someone put some higher power bulbs in there - not the case for sealed beam units.

Anyway, the chassis wiring has a black plug connector to the headlamp housing. I believe yours likely has 4 prongs/sockets. You might try turning the lights on with this plug disconnected. If the problem persists the problem is in the chassis wiring. You will need a multimeter to check either side of the issue, but unless you are willing to short the fuse and watch for fire, not recommended, you will need to acquire the tool. You will be looking for closed circuits with the light switch open (off). This is relatively easy - you check for a path from any of the contacts in the plug/socket to ground, other than the ground (usually a brown wire, and you can pop the connector open to find the brown wire if you need to - inspect it and then open it carefully, note which wire is brown and snap it shut). With the light switch off, there should be no path from a non-ground wire to ground so you can narrow down the culprit. I have not had a problem on this side, ever, so I can't be of much help if yours is there. Just be aware the starter switch and light switch are the central power distribution points.

If the problem does not reoccur with the plug to the headlamp housing unplugged, the problem is between the plug/socket and the connector to the bulb. Again, you will need the multimeter to find the problem. You will be checking for continuity between ground and one of the connections when there should be none (no bulb in place). This is a relatively easy task. With no bulbs there should be no closed or completed circuits.

Good luck,

Jim

[darkman]

Gotta postpone my testing until tomorrow. A thunderstorm washed me out

Yes Jim, even with all the connectors disconnected the fuse blows as soon
as I turn the headlamp switch. I used the Sylvania 9004 bulb (45/65) that
the AutoZone book specified.

I'll start back testing in the a.m. and report back.
thanks

[brasche]

Wrong Bulb, that's the answer.

People sometimes try to substitute the HB5/9007 bulb for the correct HB1/9004 bulb to get higher wattage low beams. This is a total fail.

First, although the two bulbs have the same connector, the pins are not compatible. Specifically, the low beam positive/negative pins are reversed. Be thankful for fuses, otherwise something would have melted.

Second, the HB5 bulb doesn't fit property in the light fixture. It will stay in place but the improper fit results in the light beam being unfocused and thus defeating the attempt at better lighting.

Third, the HB5 filament is oriented differently from the HB1 bulb, again causing the beam to be poorly focused and defeating the attempt at better lighting.

The HB1 bulb is keyed to fit to the proper depth and has a horizontal filament that matches the rectangular shaped reflector dish.

[vstech]

Except he is using a 9004...

5 years ago...

[andrewjtx]

[SD Blue]

EGAD! Take it easy on the guy! Don't blow him out with embarassment on his first post.

Welcome to the forum Brasche.

(You may now be aware that each post has a date in the dark blue area, just above the name.)