Toy - low voltage at starter jumper

[RatLabGuy]

93 Toy, essentially stock.
Few weeks ago I was having issues w/ my battery, temp. swapped it w/ another. That one was smaller and had poles on wrong side, so I had to mount it w/o the bracket tight. Worked great so of course I forgot to fix it right
Today I'm driving and it studders a little randomly, then 30 secs again but this time dies completely.
Discovered it looks like the battery hold-down bracket had slid over and hit the positive battery terminal, it was really hot. I'm guessing it shorted out and caused it to stop.
Fixed it all up, but now it won't start. W/ key is Start, I can hear the click of the relay, and all the elec. stuff gets dim, but no starter movement. Replacing batteries didn't help..
I pulled the jumper wire from the starter, ran a long wire and measured only 7.5V coming off it while trying to start. Interestingly this also didn't change any behavior of what I see/hear in the cabin.

Soo... any ideas where to look? I'm assuming my short caused something to heat up and melt, but it's obviously still connected b/c it isn't 0V. The fuse under the dash looks fine. Is there a desperate big one somewhere else for just the starter jumper aside from the relay?

Related - I realized the stock ground from the battery is a really wimpy cable, and I cannot tell where it goes b/c it is bundled w/ all the positive stuff. I assume it connects to the engine somewhere? Where? I'd like to confirm the other end and make sure its all well grounded. Everything else electric works fine though.

 

[moldman05]

I would double check the ground wires/cables

 

[RatLabGuy]

I would double check the ground wires/cables

It's good on the battery end, but as I asked above I'm not sure where it contacts the block.

 

[moldman05]

Check voltage between negative battery post and clean spot on engine block when engaging starter. Should be less than a volt or two.

 

[Jason W.]

Fuseable link melted off the positive side. May even have one inline of the leads coming from the battery.

 

[RatLabGuy]

Fuseable link melted off the positive side. May even have one inline of the leads coming from the battery.

Where? I have found no such fuse.

 

[Jason W.]

I have seen on toyotas industrial equipment many times. When a battery is shorted out there are fuseable links. ( wires designed to melt) that will react to the short to ground / high amperage. I was putting that outthere , good bet they use them in the.older trucks too. Check the wires other than the main cable cing from the battery to see if any melted into, somrtes they will look OK but be melted inside, this can cause your issue.

 

[Fabrik8]

What is the battery voltage at the battery posts with no electrical loads on it? Does it look like the battery actually survived the short to the holddown?

You can check the health of the grounds by checking voltage between the block or starter case and the ground terminal on the battery while starting. If you have a bad/corroded/loose ground, you'll see a voltage difference between ground points. Blindly assuming that the grounds are electrically the same when troubleshooting a problem like this can make things very confusing, and can often completely mask a problem. I would do this check first before doing anything else, even if everything is fine it's a good sanity check so you know exactly where you stand (with the grounds) and can move forward with troubleshooting the power side of things...

You most likely won't see a voltage difference between ground points with no current flow (per Ohm's law), which is why it needs to be checked while starting.

You measured 7.5V between the end of the long cable and a ground point it sounds like; which ground point were you referenced to?

 

[RatLabGuy]

That is a good point.
the 7.5v was between the jumper wire (the small wire that tells the solenoid to flip) and the ground lug on the battery.

As an aside - the fun part is getting these measurements while starting, working by myself... need to be in the cabin w/ a foot pushing the clutch in and turning the key... so I have to run a long wire (used battery cables) between my meter and the contact points. I'd rather measure right at the joints... later this weekend maybe I can get my son involved.

 

[Fabrik8]

The long wires to the multimeter won't matter very much. The meter input impedance is very high, so the meter draws extremely low current to take a voltage reading, so voltage drop from wire resistance will be very low on those long wires.

 

[RatLabGuy]

Got it!

Yes, for future reference, the '86-95 Toys use both an 80A main fuse (knew that), and also a "fusible link" wire that is the main positive from the battery to that 80A fuse, connects up under the fuse block. It's designed to fail w/ too much heat.
Although the wire showed no visible sign of damage, and measured only 0.4Ohms resistance, it just felt kind of flimsy at the terminal connection so I replaced it w/ a beefy 4Ga wire, and the 80A fuse for good measure. Started right up. Turns out my battery is pretty bad too, it loses charge super quick... only 1 yr old, taking that bad boy back to Wal-Mart tomorrow.

So in other words, Jason W. wins the cookie on this one.

I'm still not real confident of the grounding in this truck, just seems to me the one wire from the battery is pretty thin (and I still need to figure out where it connects to the block).

 

[catfishblues]

Just for safety's sake, you can buy fusible link wire at the parts store and make up a new one. It's based on gauge and length of the wire. You'll find it with the fuses. It may have saved some wiring by failing this time. I know I'd feel better with the factory style replacement in place. Glad you found it, though.

 

[Fabrik8]

The small ground wire is fine for starting, because its a very short duration. Wire sizing is based on temperature rise for a certain amount of continuous current, so you can use a fairly small wire if the temp rise is small because the duration is short.

 

[RatLabGuy]

Just for safety's sake, you can buy fusible link wire at the parts store and make up a new one. It's based on gauge and length of the wire. You'll find it with the fuses. It may have saved some wiring by failing this time. I know I'd feel better with the factory style replacement in place. Glad you found it, though.

Didn't actually see any at Advance when I went to get the fuse. Been hunting around and nobody has an OE wire (it had a metal plate crimped on the end to match the fuse block) so I'll have to order one. Problem is I don't know exactly what the original gauge was, this one had a small wire at the batter end and a bigger gauge at the fuse end and changed in the middle.
Been reading a lot about this on the Toys, apparently most people just replace w/ a 4Ga wire and have not found any complaints of issues. Just can't get my head around what it does for you. The wire goes right to a fuse, everything is either behind that fuse or some others that T off of it. So why not just have a thicker wire and the fuse, which is cheaper, easier, and more obvious to replace?

 

[RatLabGuy]

The small ground wire is fine for starting, because its a very short duration. Wire sizing is based on temperature rise for a certain amount of continuous current, so you can use a fairly small wire if the temp rise is small because the duration is short.

As long as (a) the ground connections are healthy, (b) the battery is healthy, and (c) the starter is healthy, yes. But if either are less than ideal, then the heat rise from resistance will be much faster, so heavier gauge (or just more contacts) compensates (a little).

 

[Fabrik8]

As long as (a) the ground connections are healthy, (b) the battery is healthy, and (c) the starter is healthy, yes. But if either are less than ideal, then the heat rise from resistance will be much faster, so heavier gauge (or just more contacts) compensates (a little).

If the grounds are slightly bad, or the battery isn't quite healthy, your voltage at the starter is lower and therefore your current is lower, which makes the heat rise slower.

The only way to more heat rise (not faster, just greater) is if you need to engage the starter longer to compensate for something being bad, but that doesn't make the best rise faster. You would then need bigger wire for the artificially long starting time. I think that may be what you're getting at...?

Your starter is not a constant current load, its just a big resistor/inductor that spins, so if the voltage across it is lower from a poor ground or bad battery, the starter current is lower and therefore the ground current is lower.

I agree though, it would be better to increase the wire size to be thorough and help things out a little.