Main fuse keeps melting

[Buzzer104]

So I screwed up and connected up jump leads the wrong way round on my 03 ford ranger and blew the main 80 amp fuse but now the replacements keep melting until they fail. Truck starts up fine and everything seems to work I even bought a new battery .. I've checked some of the cables for shorts but nothing yet. I'd be so grateful for any help with this one. Thanks

[GreenV8S]

How much current is going through the fuse before it blows?

Is the fuse between the battery and alternator, or alternator and fuse box?

[dhutch]

Buzzer104 said:

So I screwed up and connected up jump leads the wrong way round on my 03 ford ranger and blew the main 80 amp fuse but now the replacements keep melting until they fail. Truck starts up fine and everything seems to work I even bought a new battery .. I've checked some of the cables for shorts but nothing yet. I'd be so grateful for any help with this one. Thanks

Very hard to say what it might be, I dont know the details of the vehicle, when the garage did this to my old car they had to replace the alternator but otherwise all was well.

[Penelope Stopit]

First things first, disconnect the alternator as the diodes should have blown and some will have gone short circuit

[Buzzer104]

Your a genius, alternator disconnected and fuse is good. There's no way to repair the old one s there?

[tapkaJohnD]

Got to eBay, look for "rectifier kit" choose one that fots your alternator.
You might have to do a bit of soldering.

Or, just get an exchange unit.
John

[Buzzer104]

Your a genius, alternator disconnected and fuse is good. There's no way to repair the old one s there?

[Penelope Stopit]

Glad to be of help

As mentioned above, if you can find a replacement rectifier plate you will be able to unsolder the damaged one and solder in the new one

[Buzzer104]

I took the plunge and just bought a new alternator but fuse began to melt, am I right in thinking there's a short on the alternator cable?

[Penelope Stopit]

Disconnect the alternator and post back the result

[Buzzer104]

Disconnected, fuse stays intact

[Penelope Stopit]

Is it possible to connect the alternator up incorrectly? If the answer is no, there is a short on the new alternator

If there is a short on the new alternator
Did you possibly over-tighten the main alternator positive terminal and damage the insulator?

[Buzzer104]

It's connected correctly and insulator is in tact, was never overtightned
Damaged harness?

Edited by Buzzer104 on Thursday 14th March 17:44

[Buzzer104]

Or the new alt is DOB

Edited by Buzzer104 on Thursday 14th March 19:25

[Penelope Stopit]

If the fuse stops melting by gently disconnecting the alternator without pulling on the loom, the chances are the alternator is faulty due to you not having any problems before jump starting

Is the alternator heavy positive cable very tight around the engine or alternator body and shorting out when you pull on it to connect it up?

I am pretty sure you know the battery is connected the correct way and also that it hasn't been reverse charged meaning that the polarity is opposite to what it should be

[Buzzer104]

Battery's new so no chance that the polarity has switched. I just started it up and disconnected the battery and it continued to run so I know the new alternator is good also fuse stayed in tact. Cables from battery to fuse box have been checked for shorts. I'm really flummoxed with this one

[Penelope Stopit]

Don't disconnect the battery when the engine is running as it will damage the alternator