1987 m923a1 855 cummins starting problem

[chevy427]

New truck owner,working thru the problems...replaced brain box...but when the temp drops below freezing everything works but wont crank over!...temp goes above freezing truck cranks right over! any Suggestions? thanks for your help!

 

[porkysplace]

The first thing to do is load test your batteries .

 

[chevy427]

2 are good...2 are week...just went out and she cranked over cause she was sitting in the sun!but not enough to start...a block heater is in my future...

 

[chevy427]

and a couple new batteries!

 

[MtnSnow]

Charge up your weak batteries and retest them or eliminate them as they are drawing down the good batteries