1988 MR2, left headlamp goes out. I replace it, turn on lights and it's VERY dim, yes it's a brand new headlamp. Flip to highbeams and it goes even dimmer, right headlamp working fine. I think it's got to be a fuse but, it's late in the evening and I need to get to bed to get up early for work, yatta yatta yatta...
Next morning I drive to work then at end of day I get in, start up and turn on lights and now BOTH headlamps are VERY dim. Put on highbeams and right lamp goes to highbeam left lamp goes super dim, have to drive home like that.
Questions:
This has got to be a fuse right?
It should just be a matter of replacing the fuse and everything is back to normal yes?
Does anyone know which fuse box the headlamp fuses are in?
All help greatly appreciated because unfortunately I don't have access to the mechanics manuals...
Check voltage drop in the lighting circuit.
Could be a bad switch, bad grounds, bad connectors, flaky wire ...
Good lighting info HERE.
Make sure to check the voltage at the bulb with the circuit turned on. Here's some basic troubleshooting info:
http://www.motoiq.com/magazine_articles/id/1952/basic-electrical-troubleshooting.aspx
DrBoost
PowerDork
11/29/12 9:47 a.m.
Dim lights almost always equal a bad ground or a melted connector (usually caused by a bad ground).
ncjay
Reader
11/29/12 10:00 a.m.
In my experience either fuses work or just blow out. The funky voltage problems would have me checking the headlight switch, the ground connections, or just a dirty or loose electrical connector. There might be a headlight relay involved somewhere as well.
Given that it's only one side (at first), start with things that are unique to that side. Like a ground 
or a bad connector. It's less likely that a failing switch or relay would affect just one side.
wbjones
UltraDork
11/29/12 10:42 a.m.
ncjay wrote:
In my experience either fuses work or just blow out. The funky voltage problems would have me checking the headlight switch, the ground connections, or just a dirty or loose electrical connector. There might be a headlight relay involved somewhere as well.
that's what fuses do ... they either pass current or they don't ... never just a little bit ..
I question how well you installed the plug on the light. That's the variable. Generic fix would be to pull it back off, and shove it on again. Make sure it goes all the way on.
wbjones wrote:
that's what fuses do ... they either pass current or they don't ... never just a little bit ..<img
I beg to differ.
Yeah, that's a 3-phase system, but the fuses behave pretty much the same. Some have high resistance where they shouldn't.
In reply to slantvaliant:
But would a faulty fuse cause one headlight to malfunction, then the other as well. I'd say its unlikely the source of the problem.
I doubt the fuse is the OP's problem - see my first post.
In the second, I just wanted to correct the impression that fuses "pass current or they don't".
Besides, it was an opportunity to post one of my thermographs. 
On mine it was the alternator giving up the ghost.
Thanks for the suggestions guys. Yelch and to think I had the silly notion it could be something simple I could just take care of in about 30 mins...
certainly sounds like a ground problem to me
It could be a quick fix. Check anywhere you see a connection. Even a quick unplug/replug can sometimes get things working. And don't forget to check the chassis ground.
MOST lighting issues are quick fixes... treat it like a fiat and check the grounds
wbjones
UltraDork
11/29/12 8:23 p.m.
slantvaliant wrote:
wbjones wrote:
that's what fuses do ... they either pass current or they don't ... never just a little bit ..<img
I beg to differ.
Yeah, that's a 3-phase system, but the fuses behave pretty much the same. Some have high resistance where they shouldn't.
apples to oranges ... that's not going to be his problem ... if they're bad, they'll eventually blow ... the high resistance leads to high temps ...
I worked at Bussman ( you know Buss fuses ) and while learning to use the correct length of time of "current on" to do the soldering/brazing I managed to blow up many fuses ....
wbjones wrote:
slantvaliant wrote:
wbjones wrote:
that's what fuses do ... they either pass current or they don't ... never just a little bit ..<img
I beg to differ.
Yeah, that's a 3-phase system, but the fuses behave pretty much the same. Some have high resistance where they shouldn't.
apples to oranges ... that's not going to be his problem ... if they're bad, they'll eventually blow ... the high resistance leads to high temps ...
I worked at Bussman ( you know Buss fuses ) and while learning to use the correct length of time of "current on" to do the soldering/brazing I managed to blow up many fuses ....
I used to sell Buss fuses (wholesale house) - that was a fun job, wish it had paid more (or that the idiots who paid for my education would have been the ones to offer me better work the countless times I applied for new positions...).
The thermal image is way cool...
wbjones
UltraDork
11/29/12 8:43 p.m.
OldGray320i wrote:
wbjones wrote:
slantvaliant wrote:
wbjones wrote:
that's what fuses do ... they either pass current or they don't ... never just a little bit ..<img
I beg to differ.
Yeah, that's a 3-phase system, but the fuses behave pretty much the same. Some have high resistance where they shouldn't.
apples to oranges ... that's not going to be his problem ... if they're bad, they'll eventually blow ... the high resistance leads to high temps ...
I worked at Bussman ( you know Buss fuses ) and while learning to use the correct length of time of "current on" to do the soldering/brazing I managed to blow up many fuses ....
I used to sell Buss fuses (wholesale house) - that was a fun job, wish it had paid more (or that the idiots who paid for my education would have been the ones to offer me better work the countless times I applied for new positions...).
The thermal image is way cool...
after Bussman moved their plant to China, I worked at a plant that made resolvers that went into the FLIR ( Forward looking infrared ) used in some of our Navy and Air Force fighters
start at the light- wiggle the connector.. if that makes it better, pull it off and clean the contacts with whatever you can get in there and bend the tabs up to make the connection tighter..
if still no joy, then trace the ground wire.
if still not fixed, then keep working your way back to the switch..
this all assumes that you've got 13+ volts coming out of the alternator and into the car..
OldGray320i wrote:
The thermal image is way cool...
You should see my private collection. 
High resistance leads to low temperatures, because resistance decreases current and thus power consumption.
Fuses blow when they heat up due to increased current draw caused by lower resistances, usually a short to ground.
wbjones wrote:
OldGray320i wrote:
wbjones wrote:
slantvaliant wrote:
wbjones wrote:
that's what fuses do ... they either pass current or they don't ... never just a little bit ..<img
I beg to differ.
Yeah, that's a 3-phase system, but the fuses behave pretty much the same. Some have high resistance where they shouldn't.
apples to oranges ... that's not going to be his problem ... if they're bad, they'll eventually blow ... the high resistance leads to high temps ...
I worked at Bussman ( you know Buss fuses ) and while learning to use the correct length of time of "current on" to do the soldering/brazing I managed to blow up many fuses ....
I used to sell Buss fuses (wholesale house) - that was a fun job, wish it had paid more (or that the idiots who paid for my education would have been the ones to offer me better work the countless times I applied for new positions...).
The thermal image is way cool...
after Bussman moved their plant to China, I worked at a plant that made resolvers that went into the FLIR ( Forward looking infrared ) used in some of our Navy and Air Force fighters
Funny to see a FLIR image here.... my wife works on their military systems side. Lots of cool toys and they have a take home program too! (though it's civilian side stuff only).
