tail lamp circuit boards

ddale · Post by **ddale** » 09 Dec 2003, 08:33

I recently replaced a tail lamp in my '86 240 with one from an '87. Now I have no backup lights and a brake light dummy light going off every time I touch the brake pedal, even though the brake lights are working fine. I noticed the tail lamp circuit board part#'s don't match. Is this the problem?
And if so, are there any which are interchangeable? There's one on ebay but it is another part # altogether yet the guy is advertising it as good for any '86 240. any help would be appreciated.

ddale · Post by **ddale** » 12 Dec 2003, 09:36

followup: the back up light bulbs were mismatched causing that problem, which is fixed. Now I suspect that the reason the brake lights are working but activating the in dash warning light is because the center brake light is of the wrong type. The center light's socket is for the smallest type of the standard twist type bulb, so I used what I had handy, a bulb that is for a dome light but fits. It wasn't as bright as a brake light should be, but the standard selection at the local auto parts store doesn't offer anything brighter. I know an empty socket would activate the warning light being a broken circuit just like a burnt out bulb is, but I assumed that putting any bulb that fits would at least complete the circuit and deactivate the warning light. Now I suspect that an under rated bulb will cause the same indication. The manual calls for a 21 watt bulb to go in there, which is easy to find in the larger size which my salvage yard rummagings have showed is common in most 240's with the brake center light. I'm trying to avoid replacing the center light fixture altogether, so-
Does anyone know where I can find a 21 watt bulb in the smallest twist type size?

Volvord · Post by **Volvord** » 13 Dec 2003, 15:21

The bulb failure circuit on the Volvo works on a load balance system, the bulbs have to be the same wattage and working to balance the circuit. Your note seems to indicate yopu discovered this.

The bulbs used by Volvo are common automotive bulbs, usually 1157, 1157, and 95 all being the bulb type. I would suggest that your local parts supplier or auto store can supply the correct bulbs, but to be safe I would also recommend that you replace both bulbs at the same time.

ddale · Post by **ddale** » 27 Dec 2003, 10:57

Further update: As I mentioned above, the back up light problem was due to mismatched bulbs. Thanks to Volvord for confirming that mismatched bulbs can activate a bulb failure light on the dash. But the problem remains that the high center brake light fixture (that's the one in the back window) is for a bulb half the size of the standard 1157 types in the tail lamps. All I can find to fit are lower wattage bulbs normally used for dome or dash lights. It works (though my center light is about half as bright as it should be), but every time I use the brakes I get a bulb failure warning light. Not a big problem I know, but I think having the bulb failure warning light on the dash is a pretty cool feature and it's just the sort of thing that drives one nuts, you know what I mean?

petershen1984 · Post by **petershen1984** » 28 Dec 2003, 09:24

Hmmm.... I wonder if the Load Balance System will work with LED lightbulbs if I replace all of them.... (740 GLE). Costs three times as much as normal filament bulbs, but also a lot brighter and lasts longer.