No brake lights volvo 740/fuse/bulb/switch alltest good

briguy1960 · Post by **briguy1960** » 09 Nov 2010, 20:53

92 volvo 740 wagon, 4 cyl auto regina. Brake lights stopped working a while ago. Checked the fuse #4 --good. Shift interlock works. I replaced the brake light switch even though I think it was fine. Took the bulbs out and tested, they all work. The haynes manual shows no relays, but Judging by the thinness of the two wires going to one connector and the three wires to the other connection of the brake light switch, I cannot believe that current for the brake lights is flowing through that switch. Can Any good soul please guide me as to where I might look for an answer. If nothing surfaces I may jury rig an old fashioned non relay style of brake light system but If I can fix it properly all the better

Thanks all Volvo gurus

Brian

randyman · Post by **randyman** » 10 Nov 2010, 02:54

With the vehicle running, pull the connector off the switch and probe with test light or meter. You should have 12V on one terminal with the meter or light's other end connected to a good chassis ground. Do not test inbetween the 2 wires at the connector, this will not provide any useful info. I battery voltage is present on one of the terminals then use a jumper wire or paper clip to go across the terminals and have someone watching to see if the lights illuminate. If they do, then your new switch is not adjusted correctly, or defective. If they still do not come on then the wiring circuit from that point to the rear of the car is open.

ed7 · Post by **ed7** » 10 Nov 2010, 04:23

I know this one, me, me,. Pick me! me !
It took me a while once, but the common thread is the "bulb failure sensor". It's that orange can thing on the back left of your fuse block. I found one, when I didn't need it, at a junk yard for little. I never found out the cause on the old one, I thought it was a bum solder joint.
Ed7

Post by **billofdurham** » 10 Nov 2010, 12:28

I know this one, me, me,. Pick me! me !

+1. Once the bulbs are shown to be OK head for the bulb failure sensor.

Bill.

briguy1960 · Post by **briguy1960** » 10 Nov 2010, 22:51

Well,

I pulled the relay panel, removed the bulb sensor, sprayed the contacts, reinstalled , NO JOY! Jobber parts man quotes 160 dollars for the bulb sensor relay!!!!. Would maybe go for it if I knew for certain that was the fix. BTW, 12V at one of the two connectors. SO-------Tap a switched hot off the lighter, fish two wires with attached spade connectors to the brake pedal switch,Spade connected the two old terminals so the shift lock would work.There was already a wire for a trailer lights connections from the fuse block to the rear of the vehicle. Spliced the two brake lights together and voila, brake lights circa 1950 style wiring. Bizarrely , now the bulb failure light comes on when I apply the brakes. If I can source an known good bulb failure relay for cheap I may attempt to take it back to stock. Solved for now..........

BTW, that is one thick bundle of wires when you pull the fuse/relay panel out

B

Retired MVS Contributor · Post by **Retired MVS Contributor** » 11 Nov 2010, 05:52

This problem is common in the 740's and is located in the lamp assembly itself...Power is distrubuted to the individual bulbs by flat galvanized bus-bars within the lamp assembly...The negative (common) return does not go directly to each bulb, it runs over to each bulb, but is connected by way of a pressure contact right next to the socket...These contact points become oxydized and flow is lost...With the lamp assembly connected to power, wedge a small screw driver into this contact gap and I wager the bulb will go on...The fix after that is to either bridge the gap with solder, (my preference) or use a knife blade or other such tool to clean up the contact...The drawback to the knife blade is that it might break the plastic nubs that hold the bus-bars in place...

Jerry

siemonhg · Post by **siemonhg** » 22 Nov 2010, 06:40

As Bill stated, it's the bulb failure warning relay. Electicity for the brake lights, tail light and low beam headlights go thru this relay. For the brake lights, it goes from the fuse (always hot) to the switch at the pedal, then thru the relay to the brake lights.
I had the same problem. No brake lights and only one low beam. Replaced the relay for $80.00. Problem solved.
Shop around for a better price. I've seen them online for $60.00.

Jdullwitted · Post by **Jdullwitted** » 29 Jun 2018, 16:08

I was very lucky. I found your post yesterday. With no mucking about, and your instructions, the mechanic fixed my brake lights quickly. Thank you, a million times.

Jdullwitted · Post by **Jdullwitted** » 04 Jul 2018, 08:44

It was a good attempt, but, after two days, the dash light-out indicator is on. Only the right rear light is the one that is out, but not even consistently. Looks like replacing the board? Anyone?