Anyone understand simple car wiring....

[trevt]

...because i clearly don't.

I've a 1980's kubota compact tractor - basic diesel that has lived most of it's life outside but been rather reliable when i've needed it and seemed to appreciate basics like fluid changes, grease and new coolant hoses. However it's got me confused electrically and is threatening to go up in flames.

Recent cold weather went out to start it for some jobs but she refused and was sluggish on a recently charged battery (I take the battery out when not being used and keep it charged). Thought it's cold and decided to leave the job for a couple of weeks.

Went to start yesterday and started straight away - excellent. Killed engine so i could get everything else ready and then came to try to start again. Same problem as last time sluggish turn over as if the battery is drained. Getting dark so left it until today but put a spare battery on charge to be sure.

Today connected up spare battery and still same - sluggish as if battery is dying. Starter is turning but smelt smoke and realised a wire loop (which i now know is a slow burn fuse) was getting rather too warm. Disconnected battery.

Had a check round all connections and found nothing untoward. Went to reconnect negative battery cable - it sparked as soon as the terminal touched the post, pulled back and checked ignition was off. Then connected again - it sparked and very quickly the slow burn fuse started to smoke again - there should be no draw on the battery when the ignition is off?

I can't understand why it is drawing current, and higher than it should, with everything switched off as soon as the battery is connected.

Also confused by wiring at the starter motor:

- main wire direct to battery - expected that;
- small wire to another terminal - expected that; but
- third wire (looping through slow burning fuse) connected to same terminal as main battery cable.

Has the solenoid shorted, or a relay or the ignition itself (most of the dash lights/instruments gave up the ghost long ago)?

If i wanted to wire a "flick" switch to operate the starter (instead of the key) how do i do it?

Appreciate any help - i hate wiring.

[bearman68]

Thinking about this, I think the big heavy duty wires in your starter motor have shorted between themselves. Either send it for testing - there's little you can test without some posh kit, or replace the motor.

I started typing out a test procedure, but I don't think it's worth it - I think the starter has failed internally.

[trevt]

That makes sense.

|I wasn't thinking about the starter internals as it was still turning over. Now to find someone local ho tests & rebuilds if possible. New starters are coming in at £150 - ouch

Much appreciated

[GreenV8S]

Definitely sounds as if something is shorting, but the way you describe the fusible link getting hot when you connected the battery with the starter (presumably) not engaged makes me wonder whether there is a short external to the starter.

I guess your starter is basically the same as on a car, in which case you have battery power coming to the main power input on the solenoid, switched in the solenoid and connected (internally or externally) to the starter motor itself. That connection is not usually fused. However, that main power terminal is also commonly used to provide power to the rest of the vehicle electrics and *that* connection often includes a fusible link. The symptoms suggest you have a short to ground on that wire or something it connects to. To light up the fusible link as you describe it would probably need to be a short on a heavy cable, so I'd start by examining that cable carefully for signs of chaffing against the chassis/engine etc.

If you want to fit a push button starter switch instead / as well as the ignition barrel you'll need to connect your pushbutton switch in parallel with the 'start' circuit of the ignition switch but you should beware there may be safety implications if it makes it possible for little fingers to crank the engine without the key, possibly while it is in gear, perhaps unintentionally etc.

[Who me ?]

trevt- perhaps an understanding of how starter wiring/operation works might help you arrive at a diagnoses.
There's two sets of wiring to a starter motor.
1 = the great big thick cable from battery to starter.
2= the solenoid wiring.

A solenoid is a remote operated switch ( a relay ,with contacts capable of handling the large operating current to operate starter).
You turn key, and solenoid operates
Solenoid does two things
1- makes a heavy duty circuit to provide current via thick cable to starter motor.
2 - on modern starters, pushes starter cogs into flywheel ring.
If something is getting hot, then it usually means that an excess of current above design specs is trying to flow.

[trevt]

Thank you

The second wire, on the same terminal as the heavy duty battery cable, being the power source to all other electrics makes sense - it was that wire that confused me. I might try disconnecting it and see what happens - if the short is inside the starter the battery cable will turn hot/starter will burn out?

i'll probably not get power to the solenoid so starter won't work but if i connect the solenoid direct to battery that should engage the starter - just don't leave it connected if the engines fires!

Take your advice re small fingers etc which isn't too worrysome as i only have a teenager about who just gets the key anyway

The wring includes lighting circuits etc which don't work as is, might be as simple as blown bulbs, but i never need them. Given the number of changed spade connectors and the generally worn wiring the previous owner has had a few glitches. Hence my thought what's the simplest circuit to start and run the tractor - all i really need are the starter, alternator, glow plugs and the relay that kills the fuel when i want to stop (but pretty sure a pull lever also does that function).

All it needs is a simple circuit.

And thanks for the simple description of how the starter works, useful

[E-bmw]

Immediate over-current when connecting the negative, I would normally put down to the battery being connected the wrong way round but as you disconnected & then reconnected I am guessing you didn't remove the battery completely & so that is unlikely.

This basically leaves what others are saying gross short circuit between neg & pos.

If you have a multimeter you should be able to check for this.

[Penelope Stopit]

Disconnect all cables from the starter motor and wrap rags or bags around their terminals to prevent them from shorting to anything
Now connect the battery and see if there is a spark

If there is no spark, using a nut and bolt, bolt the starter main battery cable terminal and that other cable that was connected to it at the starter together, wrap a rag or bag around the bolted joint to prevent them from shorting to anything
Now connect the battery and see if there is a spark

Now post the result here

[bearman68]

Penelope Stopit said:

Disconnect all cables from the starter motor and wrap rags or bags around their terminals to prevent them from shorting to anything
Now connect the battery and see if there is a spark

If there is no spark, using a nut and bolt, bolt the starter main battery cable terminal and that other cable that was connected to it at the starter together, wrap a rag or bag around the bolted joint to prevent them from shorting to anything
Now connect the battery and see if there is a spark

Now post the result here

I can see what you're doing there, not a bad plan to be fair.

[GreenV8S]

Maybe use a test lamp instead of looking for a spark.