If all the lights are coming on but not flashing then what you have is
insufficient current draw in the circuit as a whole. This could well be due
to one or more bad connections, including bad grounds, but could also be due
to incorrectly rated lamps, or tired lamps. It is quite likely to be a
combination of things.
You could start by checking the grounds by connecting a voltmeter between
the casing of each lamp to a known good ground in turn while the lamps are
illuminated. Ideally you should not see any voltage but are bound to see
some. Comparing the good side to the bad may be helpful.
Then try the same thing again but with the voltemeter connected from the hot
terminal (or as close as you can get it) to a known good 12v.
Don't be tempted to stop at the first bad connection, which when cleaned,
starts them flashing. Check them all.
or if that doesn't work try
From: John A. Walker <email@example.com>
To: firstname.lastname@example.org <email@example.com>
Date: 03 August 1999 18:08
Subject: Turn Signals
>Okay, Here is one.
>Right side works fine.
>Left side lights come on but do not flash.
>What would cause this?
>Do I have a bad ground somewhere? If so, I am not sure where. :(
> John Walker
>~= Early 1974 MGB =~
> In Progress :)