Adding a Tach to a motorhome...
 

My grandparents recently purchased a 1978 Ciatation Bendix 31' motor home. It has a V8 454 under the doghouse. We clocked it at 60 mph, it gets 7.2MPG, its 109 dollars for 3/4 of a tank of regular. We want to hook a permanate tach up to it to see what RPMS its sittin at. My dad says a tach only needs 3 wires, one for the coil, one for the dist, then the light, or so he remembers. How would i go about hooking one up?

most do have very little wiring to do; typically you will need:

A +12v source (should be able to find one in dashboard, only hot when key on)
A ground (probably also under the dash)
A lead to the negative side of the coil (this will probably be the longest wire run you have)
A connection to the dash light circuit (again under the dash)

Most aftermarket tachs will come with instructions regarding wiring--just go pick one up, a few wires and you're done.
A lot of the ones I've seen have a switch in the back to select 4-6-8 sylinder mode; just make sure you get one that will work with an 8 cyl motor and you'll be fine

Makes me curious as to what a stock 454 red lines at..