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Hi BellaBoo,
Sorry for your problems with your 1985 Volvo 700-series and a tardy response to your question.
I imagine another brickboard member with direct experience to the foibles of the mid-1980s-era shall respond. Never owned a 700-900-90, yet have repaired them. (Not so much the '90' series.)
Causes are numerous. Yet, as ever more RWD brickboard.com (www.brickboard.com/RWD/) posts demonstrate, corrosion at any point along a conductive circuit.
In your instance, from battery 12 VDC+, through connectors, to the fuse box, to the hazard switch, the relay, and the four light bulbs at each corner to flash.
Where conductive materials bond (securely make contact, sometime with mechanical reinforcement, like where fuse contacts secure in the fuse holder, or the light-bulbs touches the positive and negative contacts in the light bulb holder).
You could also have a short.
Yet I'll bet corrosion at the fuse box, and related bonded connections along the related circuits.
The 700-900-90 suffer from a design that uses much longer conductive runs as, behind the ashtray at the center dash console, is a relay platform made of ABS plastic. Corrosion forms where both the wire harness terminates at the relay platform and where the relays make contact between the metal relay pins, like the turn signal / hazard flasher relay. (Though the turn signal and hazard flasher may be unique and on separate fuses.?
Once corrosion forms along a conductive pathway, as it has in ever single RWD Volvo, corrosion can form at other bonded interfaces (connectors, and such).
You'd need literacy with multimeters so you can perform unpowered circuit continuity tests and power circuit voltage tests.
You'd have to:
- inspect the damage from the melted fuse. May need to replace the fuse holder
- get under the dash, pull the fuse holder out, and wiggle wires and inspect the damage from the melted fuse.
- Find continuity faults to ground (shorts)
- Correct unbalanced or missing connection to ground (A plug and unplug, a loosen and tightening of the bolt, secured to the chassis, with all the wire terminating in ring terminals attached to it.
In the 700-900-90 FAQ, we have a header title with mention of melted fuses.
https://www.brickboard.com/FAQ/700-900/ElectricalCircuitsRelays.htm
See the heading Relays and Fuses Overheating. Relays. The three bulleted solutions are all solutions for electrical continuity errors. Corrosion, broken solder welds, corrosion in crimped electrical connections. Please read the section. Can you do this sort of repair? I'll guess not?
Yet no melted fuse diagnostic or procedure to deal with a faulty 700-900 series fuse holder.
As you reside in Seattle, the Winter rains make it worse. If you have a garage or carport, great! The humidity, dampness, and tons of salt in a single snow flake environments all promote and are facility for corrosion: In the body as rust and in the wire harness connector, halting current flow and making heat on high load / current circuits at bonded interfaces.
Why some of us make use of No Ox / DeOX / dielectric compounds, and so forth, as appropriate.
When you meet with your mechanic, you can provide wiring diagrams:
Volvo 740 series wiring diagram directory
http://www.volvowiringdiagrams.com/?dir=volvo/740%20Wiring%20Diagrams
Volvo 740 series wiring diagram directory
http://www.volvowiringdiagrams.com/?dir=volvo/760%20Wiring%20Diagrams
If I resided some place near you in the Puget Sound region, I'd be glad to help in person. Yet I'm some hundreds of miles to the East North East of you, more or less, so maybe some other swarthy brickboard member near you can help?
Sorry for the clutch cables.
Questions?
Hope that helps you.
Oscilloscope Boyeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee.
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