Older Volvo Problems! 1986 240, electrical, fuse, or short?

most likely the problem will be at a harness ground point.

there are several for dash components the first place to look is the drivers side transmission tunnel kick panell remove this by turning slotted plug 90 degrees to the left and loosen the screw at the top of this panel, now slide Panel forward til edge clears console and withdraw the Panel the gang grounds are bolted to the base of the center console frame. cleaning tightening of repair of broken wires here should fix your problem.

if this is more than you are comfortable with you should either visit your local dealer or trusted independent shop.

good luck

It sounds like a major short in a wire cluster. I don't know if it could be this, but under the hood, about the center of the firewall (behind the engine) there should be an electrical system plig and socket which connects about 8 sets of wires. This connections inside this deterriorate over time, and can cause all sorts of electrical problems, especially warning lights flashing up when they shouldn't and things not working. Best to get it checked by an auto electrician, because any faulty wiring in a car can cause a fire.

It definitely sounds like there is a short of some sort in the electrical harness. Perhaps you have had a rodent of some sort visit your vehicle and gnawing on the wires.

It sounds like it is more than one wire and perhaps one is hanging loose and making contact when you brake hard. I would highly suggest you begin a search within the wires before something happens to cause a spark and create a fire.

the gear on the cable that goes in the transmission is missing a few teeth.buy a new speedometer cable and install