Have no tail lights now at all, no turn signals, or brake or backup lights.Fuses are all ok, cant figure this one out!

my mechanic has replaced computer 3xs, new distributor, replaced ASD twice. when it runs its the best its been in years, but dies. 70,000miles on van, very low mileage. he is at his wits end and suggestions on a new way to look at or check something different. any help would be appreciated.2

I need to know where the crank position sensor is located; this is a hopeful fix to this issue no one has been able to resolve; guy who sold it to me put a brand new alternator in and still had the same problem of cranking but no start constantly. I tried replacing the voltage regulator (batteries are fully charged and working when I put them in) and the computer (brain) located thru the interior engine housing on the vehicle. An auto store tech told me last nite this could definitely cause my issues, but I need to find it to replace it. Have seen on web it can be located in bell housing on transmission, behind the water pump, on crank shaft or pulley, etc.