The Big Fuse

[mark h]

My rev counter doesn't seem to work from cold ,but as soon as the car warms up it shoots back to life.I seem to remember an earlier thread saying that this is a sure sign that the big fuse between the battery and the alternator is on its way out.Can anyone confirm this fact.

Thanks

[s100 spb]

Hi Mark

Yep sounds like the alternator fuse. They break under vibration quite often. It's an easy fix and worth sorting soon as the battery will not take full charge and eventual could leave you stranded.

Here's what I learnt with my 4.5:

It’s a 100 amp fuse on the 4.5 (check if you have 4.2 that it is the same), cost £1 from any dealer.

It’s located in a small oblong box under the bell housing.

To get to it, take the top engine trim cover off. The small black box (about 1 inch long) is located right in the middle under the bell housing, a bit fiddly, but ok to get to with a simple small socket set.

Flick up the box and see if the fuse is tight as it sometimes comes loose. Replace if bust – and that’s your fix.

Simon.

[olly]

The fuse is the same on a 4.2 (& Speed 6 ?), so no need to worry about gettign the wrong fuse, as long as it's the 100 Amp !

[joospeed]

this isn't a sign that the fuse has broken .. your battery going flat is a sign that the fuse has broken (!) .. the rev counter thing is commonplace - no fault - it's just that when your engine starts and it revs a bit slow on first starting it won't register .. give it a bit of a blip on the throttle and it should come into life again. seems worse in cold weather for some reason .. musty be some electrical thing in the unit.
Howvere having said that it's always a good idea to check the fuse every so often such is the cerbie's appetite for them ...

[mark h]

Cheers chaps for the advice and especially the instructions on the fuse replacement.

Mark

[dannylt]

PS In an emergency, just bolt the two connectors together - very straightforward, and great when you don't have a fuse.

PPS Replace the damn thing every 6k so it never goes on it's own!