Switch/relay replacement

Davedaknight · Post by **Davedaknight** » 17 Oct 2004, 19:49

Is there a quick short cut to replace the relays on my 740? Or even a long cut- I can see the fuses, but nothing behind them; the radio is covering that area up. I'm talking about the brake light relay. It cost me $150.00 the last time, and now it's gone on the fritz again. My "bulb out" light comes on, but when I check the brake lights, they're on- as well as one backup light. It's making me crazy.

Kmaniac in California USA · Post by **Kmaniac in California USA** » 18 Oct 2004, 09:50

The problem you describe, with your back-up light coming on with the brake lights, does not sound like a relay problem. Before changing any relays, check the integrity of your taillight assembly grounds. The illuminating back-up light tells me that the brake light circuit is grounding through the back-up light.

Some things to consider:

The brake light bulbs are dual filiment; you have a brake light filiment and a rear tail light circuit in one bulb. An internal short in the bulb could cause one circuit to ground through the other. I would suggest changing both dual filiment bulbs with new before changing a relay.

The tail light assemblies use a thin, plastic based circuit board. It is possible that one of the light circuit paths has fractured, causing a open circuit and forcing circuit grounds through other lights. The circuit board on the left tail light of my 1986 740 GLE has a wire soldered between two portions of a circuit path. It looks like this was the past solution to a past tail light problem encountered by one of the previous owners.

I, too, have had a problem with the "bulb-out" light coming on with continued bulb operation. I have found that the bulb holder electrodes (with raised buttons) tend to indent the circuit board contacts. Then, the contacting surfaces get corroded and increase the resistance to the connections. To correct this problem, I have cleaned the electrodes and circuit boards with steel wool and lubed the contacts with silicone grease. This has done the trick for me.

If you still need to change a relay, you will need to "unclip" the fuse/relay holder behind the ashtray, and pull it out of the cavity. Yes, these things are clipped in place. The hold down clip is on the left side of the fuse block. Once you unclip, it will easily pull out, revealing the relays.

I hope that my experience will help get you pointed in the right direction.

Davedaknight · Post by **Davedaknight** » 18 Oct 2004, 17:09

Thanks!. I pulled the bulbs on both sides, steelwooled the insides and put a coat of nonconductive silicone grease, and lo! Lights- without a warning bulb.

I didn't see the clip for the fuse board, but I guess I'll find it if I know it's there somewhere.

Anyone know why Volvo mechanical engineering is so good, yet they have such third-world engineered electrical systems?

George Vrionis · Post by **George Vrionis** » 21 Oct 2004, 22:54

HI

One trick with these tail light bulb holders is to also flair out the tabs before you put it back in. Do it by bending the tabs slightly, so as to cause extra contact force when put back in place.

I think this is a common problem with 740 tail lights.

Cheers

George Vrionis
Sydney, Australia

Guest · Post by **Guest** » 06 Nov 2004, 12:33

On a 1989 740, a little tip if you don't happen to have the hands of a five year old. To get to the relays, take out ashtray, pull fuse panel cover, take off the square plastic trim around the cigarette lighter, remove the 2 screws near the lighter, you can now take the lighter and storage area out and have unfettered access to the relays.