240 headlight relay

  • Thread starter Thread starter James Sweet
  • Start date Start date
J

James Sweet

Well the second time I've seen this now so I thought I'd post a heads up
in case any other 240 owners want to check for this. In the '86 and
later cars there's a relay in the driver's footwell or behind the dash
depending on the year which supplies power to the headlights when the
ignition is on. Two cars I've worked on have experienced total headlight
failure; the parking lights will work, but turn the headlights on and
*all* the exterior marker lights and dash lights go out. In both cases I
found the plug on the relay had melted down and the connections
oxidized. I was able to pop most of the wires out of the melted shell
and put them in a "new" socket shell from the junkyard. One wire had a
burned connector so I soldered a new piece on with a connector from the
replacement socket. The relay had one burned contact blade so I replaced
it as well, and gave the pins of the "new" one a shot of DeOxit for good
measure. You can find the relay by turning the headlights off and on
while searching for the source of the click under the dash.
 
from: http://forums.turbobricks.com/showthread.php?t=134640&highlight=240+headlight+relay

"There are actually two relays used for the headlights. A small relay
was added to bypass the switch in 1986. This bypasses all the
headlight current which used to go through the switch. There is an
additional relay in the engine compartment where the headlights are
switched between high beam and low beam. This relay has all the
headlight current pass through it and is switched to either beam when
you toggle the steering column lever. On most years the high/low beam
switching relay is on the left inner fender. But if your car is like
my 93 then it's the large relay on the right inner fender. Check that
out for bad connections or possibly the relay itself crapping out.
They do go bad since there is so much current going through them the
contacts will fail."
__________________
 
James said:
Well the second time I've seen this now so I thought I'd post a heads up
in case any other 240 owners want to check for this. In the '86 and
later cars there's a relay in the driver's footwell or behind the dash
depending on the year which supplies power to the headlights when the
ignition is on. Two cars I've worked on have experienced total headlight
failure; the parking lights will work, but turn the headlights on and
*all* the exterior marker lights and dash lights go out. In both cases I
found the plug on the relay had melted down and the connections
oxidized. I was able to pop most of the wires out of the melted shell
and put them in a "new" socket shell from the junkyard. One wire had a
burned connector so I soldered a new piece on with a connector from the
replacement socket. The relay had one burned contact blade so I replaced
it as well, and gave the pins of the "new" one a shot of DeOxit for good
measure. You can find the relay by turning the headlights off and on
while searching for the source of the click under the dash.
Click to expand...

Interesting timing on your post...
A while back, I replaced the headlight switch on my '83 (no relay,
afaik) because the original fell apart.
Last week, turned on the headlights, they blinked then nothing. No
running, no dash, nada.
I could hear the faintest sizzle from under the dash occasionally as I
switched them on and off.
Checked fuses, etc., then reached behind the dash to check the plug on
the switch. That was the source of the sizzle. The plug had worked loose
and melted most of the plug sockets.
Managed to push it on enough to make contact until I can get a new plug
from the boneyard.
Surprised the fuse didn't blow. More surprised it didn't burn to the ground.
 
Interesting timing on your post...
A while back, I replaced the headlight switch on my '83 (no relay,
afaik) because the original fell apart.
Last week, turned on the headlights, they blinked then nothing. No
running, no dash, nada.
I could hear the faintest sizzle from under the dash occasionally as I
switched them on and off.
Checked fuses, etc., then reached behind the dash to check the plug on
the switch. That was the source of the sizzle. The plug had worked loose
and melted most of the plug sockets.
Managed to push it on enough to make contact until I can get a new plug
from the boneyard.
Surprised the fuse didn't blow. More surprised it didn't burn to the
ground.
Click to expand...


In these cases, the lamps limit the current so the fuse doesn't blow,
but a bad connection has a high resistance which dissipates power in the
form of heat. The heat makes it oxidize and increases the resistance
which increases the heat, so what happened is not surprising. Thankfully
the plastic is flame retardant, so while it will sizzle and melt, it
generally won't burst into flames.

On the older cars, it's a good idea to rewire the headlights with
relays, they're brighter that way too.
 
James said:
In these cases, the lamps limit the current so the fuse doesn't blow,
but a bad connection has a high resistance which dissipates power in the
form of heat. The heat makes it oxidize and increases the resistance
which increases the heat, so what happened is not surprising. Thankfully
the plastic is flame retardant, so while it will sizzle and melt, it
generally won't burst into flames.
Click to expand...

....but the duct tape I wrapped around it to hold it on, might.
On the older cars, it's a good idea to rewire the headlights with
relays, they're brighter that way too.
Click to expand...

For sure, going to do that.
 
You must log in or register to reply here.
Back
Top