Hi GAcyclops,

A 1998 Volvo 90 series? Sedan or Wagon?

There may be an arcane Volvo voltage-balancing thing. Doubt it, through.

From the 700-900-90 Volvo FAQ:

https://www.brickboard.com/FAQ/700-900/ElectricalLightingHorns.htm

Click FAQ abopve to access the whole thing and read it all.

Also, we do have some wiring diagrams for your 1998 Volvo 90-series:

http://www.volvowiringdiagrams.com/?dir=volvo/S90%20V90%20Wiring%20Diagrams

In this directory is a 70 megabyte PDF of the wiring diagram for the 1997-98 Volvo 90-series.

So, I can't guess as to the circuit layout. I'm unsure of the white reverse lamps are wired into a bulb out sensor on your 98 90-series. Doubtful.

This is a beeper that fits like bulb into the tail light assembly. You have only one? Can you test the beeper from your 990-series in another car so you know it works.

If checked for good connection to ground between the tail light?

Else, study the wiring diagram. Someone else that also owns a 90 series may chime in with the fix it solution.

Hope that helps.

Duff.