Have 2002 Cad. Sev.that battery was disconnected pos. first, now the tach quite, turn sig. and speedo. quite has obi 2 readings of P0507 P0650 and P0741 can you help PLEASE?

Most vehicles power the tach from the same circuit as the other instruments. So if the speedo and fuel gauge work the tach probably has power. May not have a ground signal from the engine computer.

use a scanner to reprogram the CPU unit in the ECM as it probably has become corrupted after a long period with out power to it.

ok iif the instrument cluster does not work.. before i give a solution can you tell me if it have atach and temp gage not a temp gage witha idiot light but a actual temp gage.. because if temp gage and fule gage hands are not in their proper place like if yo uhave a 1/4 tank of gas and it reads way past full and the temp gage is gone out of site way past say 240 degrees then it is your speedo head .. have this trouble the other day on a chevy 2002 cavalier.. replaced the head and wahla the car started. it seems the speedo head is tied in with the computer system on these cars.. and if the tach is not working you need not worry if you cannot find a head with a built in tach.. a normal speedo head with out the tach part will also work.. just when you change the head count the pins on the old one and compare it to the new one if they match then just plug it in and car should start..

Try disconnecting the battery for a few minutes alot of times tis can reset it. be sure and disconnect the negative side.

I had the same problem with my 2003 Ford Explorer. I disconnected the battery, which give the relays a chance to reset.
Clean battery termals reconnect and all good.

Since the Speedo and Tach both quit working and they use separate sending units, I would be looking for a common electrical plug they share under the dash behind the speedo. When you find said plug check to make sure that it is plugged in securely. if it seems to be plugged in well unplug it and then replug it just in case the contacts were getting a bit dirty or corroded.

bigc

Pull the drive cable out of the back of the speedo and try to turn it. If it turns you drive cog in the box is worn out and needs to be replaced.If it dose not turn your speedo needs to be replaiced.

replace the cluster

More then likely the tiny electric motor called the "stepper motor" is defective, a common failure.

I'd probably start with cleaning my connections at battery, & making sure my battery has a full charge. If not cured, maybe a new battery is required. If it will start with a jump, try running it for a couple of minutes with boosters on, and if all appears o.k. , change your battery.