Hi,
I recently bought a 89 D150 from my cousin with the intention of fixing it up and getting it on the road again. The first few days it was home, it started everytime without a hitch (coldest I started it in was probably -10C). Now however, even with a battery charged up to 12.4, it hardly turns over and when the battery was tested again, it was sitting at 11.7. I'm positive nothing is being left on to drain the battery, and if if boosted with a booster pack or another vehicle, it starts just fine. Could it be my battery/starter cables, or something else? Tried it with two different batteries.

Thanks!

 

Sounds like it could be the battery, Take it somewhere and have it load tested.

 

If not the battery it may be the starter. Under a load with the added drag of a cold engine (thicker oil, etc...) it may not have enough torque to spin it.