How to tell if it's the battery or the cable?

[AlbionWood]

Tractor always starts right up, but suddenly won't even turn over. I get a click (relay or fuel solenoid?), then nothing, and subsequent attempts don't even produce a click. Voltmeter shows 12.45 volts across battery terminals, same across connectors. Checked for voltage across connection (battery post to connector) while turning key - zero volts (so connection is good). But under starting load, voltage across battery posts drops to low single digits. Does this mean the battery is bad, or is it still possibly a cable connection (maybe at the starter solenoid, or at the chassis ground)?

Took battery out and put it on charger - shows 100% charge. Put it back in, same problem. I had this exact problem 3 days ago and fixed it by filing the battery posts and connectors until bright, charged battery and reconnected, started right up. Today it's dead again, even though the connections look fine.

Wish I'd thought to check for voltage between battery terminal and starter bolt under load, before I took the cable off. Tomorrow I'm getting a new cable anyway, if they have one in town, this is the original and it doesn't look too good. Voltmeter shows 0.5 ohm resistance, which seems high for a 3-foot length of cable.

 

[breaksteel]

Sounds like a bad starter. You can use jumper cables to test it. Black to ground and red to the starter post. If it doesn't crank then it's the problem.

 

[cgutenschwager]

It could be a bad cell within the battery, I've had that before. If you take it to an Autozone or similar, they can put it on their machine and tell you before you replace it. I also had to replace the positive battery lead on my '88 F450 Dump due to corrosion within the cable (it was $250, ouch!). The jumper cable trick that breaksteel talks about will tell you if its the cable. Is it possible there is an interlock switch malfunctioning? When you don't even get a click it could be an electronic issue.

 

[AlbionWood]

breaksteel - You mean the starter motor itself, right? Do I need to disconnect the leads from the solenoid before jumping it? Or (shudder) do I need to dismount the starter motor and bench-test it?

I reconnected this morning and tested some more, after charging the battery. Initial voltage 13.04 across posts. When I test across the battery posts with key in start position, voltage drops down to about 2, then climbed back up to about 6, then fell back to 1.5 before turning the key off. Then I tested from positive post to solenoid stud, with key in start, only 0.1V - so I guess it's not the cable. (Too bad.) From solenoid stud to starter motor housing there is a voltage drop, less than half a volt. After all that testing, battery voltage now down to 12.24.

It's a long trip to town for parts, so I'd like to know if I need a starter (which they will probably have to order). If anyone can walk me through the procedure for testing the starter motor that would sure be appreciated!

 

[Soundguy]

test with your meter at the battery terminals. i mean directly on the posts. not the cable ends. scratch the meter leads intot he lead posts and have someone hit the starter.. see if the battery dips under load.

can also test from bat hot cable across cable to starter. ie.. 1 lead on starter stud.. another on bat hot post. hit starter.. see what voltage drop is occuring

 

[AlbionWood]

Soundguy, I did exactly those tests this morning, as mentioned above. Testing across battery posts shows a HUGE voltage drop under load. Bad cell in battery? Or bad starter drawing all the juice?

Across cable to starter shows 0.1 volt.

Guess I should try jumping the starter motor, but I need a verified good battery first. This one was purchased in October 2009 and is a monster, I think 900 CCA. Getting it in & out of the compartment is about all my old back can handle.

test with your meter at the battery terminals. i mean directly on the posts. not the cable ends. scratch the meter leads intot he lead posts and have someone hit the starter.. see if the battery dips under load.

can also test from bat hot cable across cable to starter. ie.. 1 lead on starter stud.. another on bat hot post. hit starter.. see what voltage drop is occuring

 

[Soundguy]

use yer truck bat as a test.

got one of them carbon pile load testers? (500a ) or even the cheesy heating element/ spring type. ( 100-200a )

 

[AlbionWood]

No load testers - other than the starter, but I guess if we don't know what's going in with it, we don't know what load it is actually applying when I turn the key. That voltage drop across the battery terminals all the way down to 1.5V seems awfully suspicious, unless the starter is basically shorted.

Guess I could do it the other way round, connect the tractor battery to my truck and see if it starts!

use yer truck bat as a test.

got one of them carbon pile load testers? (500a ) or even the cheesy heating element/ spring type. ( 100-200a )

 

[Soundguy]

you want the bat cables to be a very low voltage drop. and the starter makes up the rest of the load in the circuit between the cables and starter, full battery voltage will be drpped. and yeah.. the starter will read like a near dead short on a meter.

 

[George2615]

1. Check to make sure your ground cable has a good connection to the frame. You cleaned the ends at the battery already.
2. When you do get it started does your volt meter show at least 13 volts. If so then the charging system is good.
3. When running for a while does either cable get hot? If so that cable may be bad. Too much resistance. It may be best to just replace them. Auto parts stores have replacements in various lengths.
4. As others have said you could have a bad cell in the battery. Most any auto parts store will load test it free.