100 AMP fuse failure, symptoms and location

[Walter Sobchak]

I've suffered the battery light staying on and the car has now lost electrical power again after the battery was charged so I thought it likely to be the alternator but someone in another thread mentioned the 100 AMP fuse.
The car has been sitting for a few weeks so it had a flat battery and I tried to crank it over, it then ran fine for a while after the battery was charged then cut out again, does this sound more like a 100 AMP fuse issue than the alternator failing?, as the car was absolutely fine before the battery first went flat.
Also could anyone post a pic or tell me the exact location of the 100 AMP fuse on a mk1 Tuscan, would be really grateful.

[DWP]

One of the problems with a battery going flat, is it can itself fail sometimes. If it was the 100amp fuse that had failed, your car would not even have started post the battery charge. Jump start the car, if it starts, it's not the fuse. Run it and look at the amp meter in the dash, is it above centre, then nothing wrong with alternator. So get a battery tester and see if it's holding a charge. If it's the battery, hard luck, changing one is the ultimate pain.

[Leadfoot]

That's not correct (for a Tuscan), the battery to starter live feed is not fused. The starter draws waaayyyy more than 100A on initial cranking (hence the battery having a "cold cranking" spec of circa 700A). If the battery has enough juice the engine will crank over.

The 100A fuse is in the alternator to starter positive wire. failure symptoms are - battery goes flat even though engine is running, battery voltage is low & decreasing with the engine running.

Voltage display should show approx 12.2v with the engine off/14 ish (depending on electrical load) with the engine running.

My '02 Tuscan has the 100A fuse bolted onto the starter itself (inside a plastic box). They usually fail through fatigue rather than blowing, & it can be hard to spot until you unbolt the fuse & it falls to bits at one end.

[crackedfinger]

Leadfoot said:

That's not correct (for a Tuscan), the battery to starter live feed is not fused. The starter draws waaayyyy more than 100A on initial cranking (hence the battery having a "cold cranking" spec of circa 700A). If the battery has enough juice the engine will crank over.

The solenoid is though. Both are right

Actually I found myself in a similar situation and spent ages faffing with the fuse as it's hard to get to on a Griff (especially on a campsite ...) and for me it turned out that is I had simply tested the alternator output with a meter I would of known in 30 seconds that it was the alternator, rather than 30 mins faffing about.

Also, if you do faff about and break the holder like I did trying to get it open, try relocating the replacement near to the top of the engine, much easier to check next time.

[Walter Sobchak]

Leadfoot said:

The 100A fuse is in the alternator to starter positive wire. failure symptoms are - battery goes flat even though engine is running, battery voltage is low & decreasing with the engine running.

That's exactly what it's doing, the battery light symbol is staying on too, the car was fine,left for a while and the battery went flat, charged up and now doing this, so seems unlikely to be the alternator, I guess it will be new fuse, or new battery.

[Konrod]

Hi Walter, the 100A fuse blown or a duff alternator will give the same symptoms, so it could be either if the battery isn't charging when the engine is running. As you can't easily get to either with the airbox in place, I guess removing that and having a look is the first step. If you are measuring voltages, please be careful with the probes being used to positive