Here is an easy timmer for glow plugs. It has an 8 second and 20 second timmer. Wire it into a relay to control the glow plugs. I am using an older one with my 6.2 now that is an 8 second. On cold days I cycle it twice for 16 secongs and works good.
Price right now is $9.98 even though the web site has them listed at $17.99.
http://www.galls.com/google/gaweb.dll