Volvo 740 Brake Light Problems

I drive an '87 740. When I brake and my headlights are not on, all 3
brake lights light up, though the lower ones are not as bright (as if
they were on as tail lights only). When my headlights are on and I
brake, the brake/tail lights do not get any brighter, only the upper
brake light illuminates. I have the correct bulbs in and the wiring
seems to be intact, is this a problem with a brake light switch? Has
anyone had such a problem? How much should I expect to pay to fix
this? Any help is much appreciated!

Lauren

 

Current is reaching the rear light assemblies when the headlight switch
is off from the brake light switch via the bulb integreity relay and a
ground is being provided through the parking light filament in the
bulbs. When the light switch is on there is no ground available hence
the bulbs don't illuminate. The problem is either a bad ground at the
circuit boards on the tail light assemblies or you have the wrong bulbs
somehow installed in the sockets. The right hand bulb holder (passenger
side US) should be white, the left side should be black, and both should
have an 1157 bulb (twin filament) installed.

Use scotch brite to clean the contact strips on the circuit board, clean
the bulb contacts and bulb holders. Remove the edge connector and
lightly clean the contact lines on the edge card surface. Use pliers to
squeeze the contacts in the connector to provide slightly more tension
on th edge card when installed. Just work your way along the connector
with the pliers, don't remove the contacts from ther respective
cavities. If the circuit board is still serviceable and the black ground
wire from the crcuit board to a grounding screw just outside the opening
for the light assemsbly is tight and clean the brake lights should work
as designed.

Bob

 

Thank you so much Bob!!! I don't know how the sockets got switched
(the white one was on the Driver's Side), but it was so simple to fix.
The volvo dealership gave me a quote of $300, I can't tell you how
grateful I am to not have to pay this amount! Thank you, thank you,
thank you!.
Lauren

 

My wife's '89 740 GL has lost both its main brake lights. The light over
the trunk (back window) still works. Bulbs are good, contacts clean. No
voltage at the rear connectors when the brake pedal is pressed & the
back glass light is lit.

The owner's manual says that fuse #4 powers the brake lights, & pulling
it kills the back glass light.

Other posts talk about 'integrity relays' & repair of same. Could this
be my problem, & if so, where are they on the 740? I've followed the
bundle from the left tail light assy up to the seat back without finding
any connectors.

Thanks,

Charlie