One, check the OD relay. Easily resolderable and a cheap fix. Next, pull
away the shift boot and check the wiring for the OD switch. There is a split
at the base of the shifter that eventually wears away the wires' insulation
to the OD (pull up on the shift knob to get it off, but be careful, as there
is not much leeway in wire lenth to the switch and it'll rip the wires off
if you yank it). I rewired my switch, and resoldered the relay in one shot.
Took 45 minutes and no problems since.
btw: search brickboard.com for pics and instructions on this.
Cheers.
