I had a bit of a stressful time driving home tonight.
i drove 230km to the city this morning trouble free drove 100km back then as it was getting dark I put my lights on and about 5 mins down the road overdrive light flashed and speedo froze. So I turned my lights off pulled over and all started working again. So I set off again drove 20km with lights off no issues. But it got dark pretty quick so I tuned them back on sure enough a bit down the road od light flashes and speedo went. But my overdrive is still working and when I press the button it turns off. All the shifting is smooth. So I just turned overdrive off and drove till about 30 km from home and my main beams were flickering like mad. Got home checked all the fuses changed the vss sensor I had a new one for a buddies truck here. I haven't taken the truck for a drive yet but i can't get the speedo needle back to zero it's sat at the maximum pin but the od light isn't flashing at the moment and my truck miles is back rather than all screwy but no speedo.

Ive read a fair few posts on the overdrive light flashing but haven't found one where the shifting and overdrive still works fine when it flashes
Anyone got any ideas?
Thanks

 

Most of the time overdrive still works when the OD OFF light is flashing.

The way to diagnose this is to get the codes read. The only other method is to start buying and installing new parts until you get lucky and find the problem.

I'd fix the headlight problem first, that may the entire problem.

 

Sounds like you need a new PSOM to fix the speedometer. Search in the '87 to '96 forum for more information. It's a fairly common problem. I'd start there and see if the headlights/OD light clear up.