When you add the WHERE to the outer join, it treats it like an INNER join.

You can break it out to two queries.  One to do the WHERE the other to do
the LEFT.

You will probably have to change the join involved to a Left Join (or
possibly a right join) since you are joining on the promoCode.  This may
give you an ambiguous join error if you try to use the right join.

I always have a problem envisioning these multi-table joins which is the
reason I like using the query grid when possible to build the query.  Here
is a stab at rewriting the FROM clause.  No guarantees.

SELECT  sky_promocodes.promo_id,
digibox.*, customer.*, engineer.engineer_code, job.*
FROM ((((job LEFT JOIN Customer ON job.customer_id = customer.customer_id )
LEFT JOIN sky_promocodes  job.job_promocode = sky_promocodes.promo_id )
LEFT JOIN digibox ON job.job_number = digibox.job_id)
LEFT JOIN engineer ON job.engineer_id = engineer.engineer_id)
WHERE job.job_skyjob=Yes