Toyota Repair: od light flashing, jumper wire, diagnostic connector

Question
I recently purchased a 1987 supra. The trans seems to shift fine, but the od light flashes. There is also a vibration that starts arond 30 and does not change if i take the car out of gear while at cruising speed. I don't know if the two or related. Feels like a driveshaft issue but I don't know. This is my first import. Thanks,
Matt

Answer
This transmission has an early type of onboard diagnostic system, when the O/D light flashes it means that the computer has found a problem, you can decipher the trouble code by opening the diagnostic connector under the hood and placing a jumper wire between the terminals TC and E1, then count the number of times the O/D light flashes, it will be a two digit code, for instance a code 12 will be one flash of the light followed by two, there may be more than one code. You can get back to me once the codes are known, the vibration, the way you describe it directly points to a driveshaft problem, possibly a bad U-joint or two.