im doing a mod today to my car im looking for a glue which will either hold metal of plastic to fiberglass?
my dad says araldite will hold metal to plactic does that sound right.

Plastics are a bit iffy with araldite, what sort of metal? Aluminium glues alright with it, but scuff and or drill it for a decent hold. If youre attaching it to fibreglass it would be even better to fibreglass it on.....that would be my choice! Glue it into position first if its fiddly then glass it.

Sikaflex :)

scuff all surfaces with a scotch brite pad, doesn't need to be too drastic, just roughen them up some
wipe all surfaces you just scuffed with acetone, leave for 10 mins
if bonding, use Sikaflex 252, if sealing use Sikaflex 227
no real need for primer unless using in a critical situation
the process always calls for a primer, people never use them so meh! 1 primer will do all three surfaces - Primer 210T
apply sikaflex in a bead on one surface only, approx 1 third the width of the surface, in a triangle.
present the two surfaces together, keep 2mm minimum thickness and clamp/brace/weigh down at least 4 hours, if not over night

done!
need to know anything else, pm me :)