Alternator rating q

I'm replacing an alternator on a Jeep. The alternator has 37 as the last
two digits on the number stamped on the body. To me that means 37 amps max
output. This jeep is set up for plowing snow with a blade and tends to
drain the battery while plowing as the amount of plowing done means the jeep
doesn't run that long. Most replacement alternators lately list two
amperages, one for idle amps and one for highway amps ... If I select a
rebuilt that claims 36/63 combination, is that most likely a similarly rated
alt. as what is on the jeep now? Or would that be a higher output
alternator? Otherwise the original alt. would called a 21/37 today??

Thanks

On Sun, 6 Jan 2008 18:19:25 -0700, "nitpik" <umpty.DeleteThis@mindspring.com>
wrote:

>I'm replacing an alternator on a Jeep. The alternator has 37 as the last
>two digits on the number stamped on the body. To me that means 37 amps max
>output. This jeep is set up for plowing snow with a blade and tends to
>drain the battery while plowing as the amount of plowing done means the jeep
>doesn't run that long. Most replacement alternators lately list two
>amperages, one for idle amps and one for highway amps ... If I select a
>rebuilt that claims 36/63 combination, is that most likely a similarly rated
>alt. as what is on the jeep now? Or would that be a higher output
>alternator? Otherwise the original alt. would called a 21/37 today??
>
>
37 amp alts were introduced in 1963 and quickly went to 42, 54, 63,
and up by the early 80's. Your alt is likely 70-90 amp rated assuming
it's newer than 1980 (about). The numbers stamped on the body 7-9
digits are the GM part #. Nearby (if it's not a rebuild) should be 2
digits and a A(mp). Better to call up a parts place and ask for the
amp rating you need and go up 1 or 2 ratings for your heavier
application.

Pete