Hi there,
If you can only connect to the secondary node, try either of the two commands below for access to the master:
user@node> request routing-engine login node 1
?
--- JUNOS 12.1X44-D20.3 built 2013-07-19 03:52:31 UTC
No alarms currently active
{secondary:node1}
user@node> exit
rlogin: connection closed
{primary:node0}
user@node> start shell
% rlogin -T node1
?
--- JUNOS 12.1X44-D20.3 built 2013-07-19 03:52:31 UTC
No alarms currently active
{secondary:node1}
user@node>
The above method is the reverse of your issue, however I just happened to be logged into the primary of my cluster.
I hope that this is of help,