MD 300 Thermo King

[Boss302]

I have a MD300 that will come on intermittently, sometimes it shows Lost Conn. Sometimes it comes on and has a code 61, display reads 8 vdc. I got it to start once and it still showed 8 vdc. Everywhere I check voltage it is 12.6vdc. I have tried a new micro, display, display harness and relay board. Anyone have any ideas or ever see this before. The customer got it to run for 20 min or so today, then it just shut down and went blank.

[abbsnowman]

I have faught these issues before. Last one was a cab command cable.

[MRW]

try replacing the black on/off switch on the side of the unit,if there is corrosion in it ,this problem can happen.
The 2n circuit goes through this switch,this is where the
cab control picks its reading up for the volt reading.

[cadwaladr]

yeah had that switch fai l it and affected the charging system lead me to despair also had earth problems cleaned em all from the battery up also check the main two lives coming from battery had them corrode inside the battery clamp always solder cables into clamps now best of luck

[abbsnowman]

Take a look at the fusable link as well.

[The Fox]

i would go for the on /off switch. they are a real pain, and MRW knows his stuff.

[djbe]

Probably the on/off switch as MRW, cadwaldr and the fox have said.
But have also seen the cab command cable shorted by rubbing where it comes out of the bottom cover to go down the bulkhead, will give the same symptoms.