The yellow jumper on the back,, does it have to be removed for my skyjack sizor lift?. i eft it on thanks ;) by the way it works fine so far .

The yellow looped wire is what controls the charging profile. If you are charging wet cell/ lead acid batteries, you may leave the wire alone. If you are charging AGM or GEL batteries, you would cut the wire to open the circuit which changes to the AGM/GEL charging profile.

is this a fully automatic charger ? this will be used for a scissor lift that has 4 of the 6 volt trojan batteries. will this auto shut off

Yes, this is a fully automatic charger. The three green LED’s indicate the charging progress. When the battery is 0 to 50% charged the 50% LED flashes. When the battery is between 50 to 75% charged the 50% LED is on while the 75% LED flashes. When the battery is between 75 to 100% charged the 75% LED is on and the 100% LED flashes. When the battery is fully charged the 50%, 75% and 100% LEDs are on. Charging time is dependent on depth of battery discharge, battery condition, and temperature. If the charger is left plugged in after charging is complete, the charger goes into maintenance mode to keep batteries charged while in storage. The charger continuously measures battery voltage and restarts the charging cycle if the battery voltage drops below about 25V. This keeps batteries charged while in storage but does not boil-out the electrolyte over time.

Im trying to replace the hbs1200-24 part no 390040-124 and cannot find it anywhere. can this be used instead?

This unit has a 19 amp out put and the one you are trying to replace is 40 amps. I do not know if that would make a difference. Sorry, I really do not know if this unit will work.