Massive ignition voltage drop

[Doe69936]

What in the ignition system could cause a large enough voltage drop to not let anything function I took off the battery to test them and the starting and hooked up the grid heater to a manual push button cause it wasn’t working and it’s been very cold lately and when I put the starter and battery’s back on every time I turn on the ignition there’s a huge voltage drop at the ignition battery terminal on the ignition switch and nothing works however if I turn it to acc position no drop and the grid heater is unhooked so it’s not that

[brokedown]

Voltage drop is normal under a heavy load like a starter... Is your starter not spinning?

[cadillackid]

are you saying that while the starter is spinning nothing works? if so, thats normal, the ignition switch turns off the power to the accessories solenoid while the starter is spinning..

[Doe69936]

I’m not explaining it right :
lights go off as soon as you turn it to the run position a the relays try to hum as if not getting enough voltage to click on the ignition switch there’s full power on the battery side when turned to the acc. Position however when turned to the ignition position voltage drops dramatically at the battery terminal of the ignition switch
Before turning the ignition switch to the start position the ignition position works as it should ie. dash lights buzzers and power goes to the starter signal wire however when hooked up to the starter and turned to the start position every thing stops working,voltage drop ect. As mentioned above until it sits about a half hour the returns to normal until attempting to crank it
It’s as if there’s a large load in ignition circuit

[Rusty]

Yeah, the computer won't like that low of a voltage. They like it above 6v min to keep that 5v reference voltage it uses stable.


I bet your gauges go wild and such?

[BlackJohn]

How good are battery connections as far being not corroded?
And the ends of the cables to ground and to the starter itself.
Would explain a huge voltage drop so would check those first of all.

John

[Doe69936]

Yes rusty they do and the scan tool goes off and one

[Doe69936]

John I see no corrosion they are rather clean on the battery side the starter side looks dirty as as any starter but nothing remarkable as far as corrosion it is possible I suppose but it seems unlikely by the look of it

[Rusty]

Originally Posted by Doe69936

John I see no corrosion they are rather clean on the battery side the starter side looks dirty as as any starter but nothing remarkable as far as corrosion it is possible I suppose but it seems unlikely by the look of it

Tell us more about your bus- cummins is a company, not an engine model.

Is your bus rusty/corroded or clean?

If it's that big of a draw, it'll get hot somewhere- hot enough to really burn your finger. Get some more eyes on it while you try?

Battery terminals are all tight. Batteries are bridged properly w/ bus bar/cable? photos help us see something you miss.

Charge the batteries between attempts. don't keep cranking or you will be changing a starter, too.

[BlackJohn]

Originally Posted by Doe69936

John I see no corrosion they are rather clean on the battery side the starter side looks dirty as as any starter but nothing remarkable as far as corrosion it is possible I suppose but it seems unlikely by the look of it

Just looking doesn't tell the story. Remove and clean the posts as well as the cable ends at the battery. When disconnected do the starter too as well as the other wires attached there. Gotta do it sometime or you get these problems of no starts. Make everything shine with a wire wheel, starter posts included, solenoid etc and try. Then coat with dielectric grease after you get it all running again.
Interior of the cables could be corroded or burnt up too so you will need to megger them for resistance or replace to be safe. Not sure of the age but likely the best idea.

Are the batteries up to snuff or is one dying which will kill the other ck and pull down the needed voltage/amperage to start?

John