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There is this book, Volvo Service Manual Repairs and Maintenance, Wiring Diagrams, 240, 1987-1988. The number on mine is TP 31076/1, 3000.04.88.
It is absolutely invaluable when these problems arise. Schematic diagrams found in the Haynes and Bentley shop manuals are copies from this book. The pictorial diagrams and the charts locating relays and connectors and ground points are not found (AFAIK) anywhere else.
Call 1-800-25-VOLVO and ask Ken Cook Publishing about getting one, along with an Owner's Manual (assuming you don't have one).
The Bulb failure warning system, which causes that bulb-out light to come on, works by pairing certain lights. Brake lights, tail lights, and low beam headlights. No others. The wires to all those lights go through the BFWS relay, where the comparison is made.
For example, the left low beam current draw must equal right low beam current draw, or the Bulb-out light comes on. Same for the left and right tail lights and all three brake lights. This all means that when that bulb-out light is on, you must check to find out which bulb is out.
It also means that anything, like oxidation on a bulb base, that effects the current draw unequally can cause the BFWS relay to trip. That's why you'll see it recommended that bulbs be replaced with pairs of the same brand.
On your car, the power to the brake lights flows from the battery to Fuse #7, thence to the brake light switch - on the brake pedal arm. From there it goes to the BFWS relay.
Three wires come out of the BRWS relay and go into a harness towards the rear of the car. The one for the high-level light goes into a connector that is not the same one as for the lower lights. Both connectors are above the driver's left toe, and a PITA to get at. Let's hope they are not the problem.
The wires for the rear lights all come to the connector to the left light. wires for the right turn signal, brake light and tail light go into a cross-car harness. All others connect to the left light.
The connector at the left light has:
White wire in #7 box...left fog light.
White wire in #8 box...right fog light.
(these two touch the same copper film on the circuit board)
Red wire in #6 box... left tail light.
Yellow wire in #5 box...left brake light.
Green wire in #4 box...left turn signal
Black wire in #1 box...left back-up light.
Black wire in #2 box...right back-up light
(These two touch the same copper film in the circuit board)
You can check for 12 volts at each wire connection. There will be none at #8 and #2, as these carry voltage from the left side to the right side.
The problem caused by old age is that where the connecting pincers clamp on to the copper film gets corroded, dented, oxidized and burnt. Everything in the connector may be just dandy, but the voltage can't get into the circuit board.
The copper film in question is on the BOTTOM side of the connecting spot, use a mirror to look at it.
Have a go at all that, post back.
Bob
:>)
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