No grid heater and no charge on 92 w250

[Hyperpack]

My 92 began givin fits with this cold weather. The grid heater does not preheat and the voltage is low because no charge, untill it warms for about 5 minutes while driving, then the heater starts to cycle as normal and it begins to charge normally. It really seems to be temperature related, the temp guage is about the same place on the way up each time things begin to work right. Where is the temp sensor that signals the Ecm to do its thing.
Thanks
Hyperpack

 

[RWherley]

The air temp sensor for the intake grids is in the top of the intake manifold, the coolant temp sensor is on the left rear of the block towards the top

 

[cerberusiam]

If this is happening only whne it is cold and works fine in warm weather likely time to replace the SBEC (computer). The typical issue is a cracked solder joint won't allow things to work unti it warms up.