Hi, I’ve got a 1990 740 turbo with a strange wiring issue. my tachometer and temp gauges only work when my high beams are off. Also the tachometer seems to not really mesure the rpm’s accurately at all, the gauge goes up and down with the revs but not enough. Any insight would me helpful

 

My sister has left town and accused my group of selling her vehicle, which she didn't take with her. It's a 1988 Volvo 740 Turbo...quirky, yet a genuine euphoria to drive with given that it's RWD, has a generally short turning span, and has a good measure of lift. I would rather not see it go, yet everything should reach an end.<BR><BR>The vehicle was unexpectedly working fine until a couple of days into being on the lookout, when it fostered a peculiar electrical issue. The circuit that controls the vault light, window switch transfers, and above all, blinkers, is biting through wires and falling flat. Two potential bombing guides come toward mind. The window switches have been dealt with previously, and one of them might be shorting the circuit. On a more speculative note, the main event of the vehicle has stains that demonstrate potential past water harm, recommending that the circuit close to the vault light is consumed or coming up short. I would incline more to the window transfer hypothesis, taking into account that they're the main things that have been played with on the circuit during my sister's responsibility for vehicle. <BR><BR>My guardians are careless to make any really meaningful difference with the issue, and it's not my anxiety, but rather I have this fixation on ensuring things in my area are precisely strong and working to their spec (PCs, hardware, vehicles, ancient rarities overall). I could go to the library tomorrow and look at the Haynes manual for the monster, and afterward attempt to decipher the wiring outlines and begin popping body boards after in some way gaining and figuring out how to utilize a DVOM (better believe it, right). Any straightforward ways of reducing analysis on this issue?





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First, look at the wires near the tachometer and temp gauges.
And check the grounding points, as bad grounding can mess up how electrical stuff works.
Besides, I’d suggest checking the instrument cluster for any wear, damage, or loose parts. Take it apart carefully and look closely at the circuit board and soldering.
You can also test the voltage in different parts of the circuit. Focus especially on areas where the wires for the gauges meet the high beam circuit. If the voltage drops, there might be a bad connection or component.