speedo bounces while cranking
 

Here's the problem this time. While cranking, the speedometer goes up to 50 mph and bounces around. Tach doesn't move at all. Mind you this is just while cranking. I recently swapped out the steering column, maybe I messed something up?

Classic case of voltage drop. On many cars the speedo does a dance when voltage is low.

Check the usual places for a loose/dirty connection. Don't forget to check the "+" junction posts on the firewall

Cheers
DD

Interesting, I just went around and cleaned/tightened all the grounds and firewall posts... guess I'll recheck everything. Thanks

Mine doesnt only bounce but the mileage goes up with it, i will be pulling the dash soon as my voltage meter has a bent needle and i picked up a complete dash for $34[very happy]

I recently encountered the speedo and miles incrementing when trying to troubleshoot a no start condition on my '85 XJ6. On a cold day I started my Jag and it was running normal and I wanted to check my heater and heated rear window switch I installed last spring. The blower motors fired up (little noisy at first) and the rear window heat switch was on, then the engine started dieing and would not restart. I turned heater and rear window defroster switch off and attempted restart to no avail - acts like no fuel (waiting for warmer day to follow Dougs Fuel Pump Circuit Checklist), but I noticed the speedo was bouncing and the miles were incrementing, thought it was due to an electrical relay issue somewhere in the car that was causing some backfeed in wiring system. I disconnected the battery (thought it might reset relays) and left it disconnected for 2 hours and when I reconnected it the speedo bouncing and mileage incrementing stopped but the car still didn't start. Just thought I would share.

The car hasn't moved for a year or 2. The battery has been disconnected and on a float charger this whole time.. I Still haven't gotten around to checking all the grounds yet