2003T Volvo Engine

[COLINFLTENG]

Having problems with oil switchs need to replace wiring loss tach indication and field for engine alterator intermittently

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[h the boat]

HI colin, Your engine is no different to many others with often similar problems. the fact that both the pressure switches and the tacho are intermittent, points to a common earthing return fault. If there is not a good negative return to the alternator, it will be intermittent and the tacho will not indicate, the same applies to the pressure switches, particularly if they are of the two wire connection type. You will have to carefully examine the multi cable from the alternator, back. At some point there will be a number of connection cables joined to one common point. this may be a form of Junction, or merely a bolt on the engine block to provide the common earth return. If the connections are made by crimping to a metalic eye, remake them all by soldering with an electrical leadflux type solder. NOT AN ALUMINIUM ALLOY solder, ( it will fall apart within weeks in a marine environment). next clean the actual point of contact of the eye with emery paper before replacing.. You may find that the common point is at the battery or near the start switch, but could be anywhere.. It may even rely on the connection made between the alternator and its mounting bolts..remove and clean them the same way, before replacing.
Let me know how you get on. Rgds h the boat