Not true, the diesels also have OVP relays in the later years (I believe 1984+) that run the EGR computer. In those years the EGR computer also drives the tach.

You didn't post the year of your SD so I'm not sure if it has the old or the new style tach setup.

The old ones use the Tach amplifier under teh hood and have a pickup on the harmonic balancer. The tach amps frequently go bad and fail intermittently as well in these setups.

The later ones have the pickup on the flywheel and are driven, as I mentioned, by the EGR computer. Most frequent failure in these systems is the OVP, either the relay itself, or the fuse on top of the unit..

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold