Peterbilt 387. Dead batterys again.

The fridge in summer would be the only thing killing my batteries. But the truck had a battery switch. 4 batteries is a lot of draw in 2 to 3 days.

 

Sounds like you've got a serious electrical drain.

 

If you think it's the transmission, find the fuse/fuses, pull it/them when you park, and see what happens.

 

Find the draw use a meter to determine the draw amount pull fuse One at a time watch the meter when you find the problem check out that circuit. Good luck

 

another way if i recall is to remove the negative battery cable, and from the terminal put a test light, at the cable that was just disconnected, clip on the other end of that test light. if nothing is on or running, the light should be off.

if the light IS on, start by removing one at a time, each fuse till the test light goes out, that's your problem (or) draw circuit.

this will also work if a relay is stuck as well.

this will take time, and maybe a helper to yell out, nope no light, or yeah, light still lit.

one can also use a test meter, voltage meter, and get the voltage being drawn as well, till each fuse and relay is pulled. you will have a better idea on miniscule volts for a computer are who knows, up to the full 12 volts, being drawn.

 

i was in the middle of my long explanation when you responded.

 

Then I'm inclined to agree with others, you have a parasitic drain somewhere in your circuit

 

there will always be such a drain, cuz the computer takes some but with the (i think) they are called capacitors? they store up that power for an extended amount of time. nearly every truck has a clock, like especially in the radio, so there is a parasitic draw there as well.

its the amount of draw, that needs to be addressed.

he never responded if he has a DEF tank, that in of itself, has a heater that stays on when the key is turned off. that can be his main current draw right there.

at my shop, we were explicitly told to NEVER shut off the power with the master switch, as that DEF tank needs that heater to be on at all times.

and when we have long holiday weekends, one would think our batteries would be dead due to the DEF heater, but they never go dead.

 

First, get one of these...

https://www.amazon.com/gp/aw/d/B00H...rds=21050t&dpPl=1&dpID=411hyJg9FTL&ref=plSrch

Lowes also carries them for about $85. Make sure it is the 21050T. Lowes has many similar looking meters but only one does DC current.

Next... set the meter to 40A DC (setting pictured)



Then clamp it around your positive or negative battery cable and note the amp draw reading.

Start pulling fuses while you have a helper watch the meter. If you still can’t find the culprit, then disconnect the wires from the alternator.

Still no love? Then start looking for wires that may be chafing against metal and wearing through the insulation. This will sometimes cause a pretty good current draw, yet won’t pop a fuse.

 

My cascadia at p&s had a def tank, when is go home on the weekends I'd be home for 2 or even 3 days, I always cut the battery off at the switch, even during the past winter, never once had an issue why my def tank freezing