Complete electrical failure

Hi,

My 90 V8 has a habit of losing electrical power completly. If I am doing something in the car that involves switching on ignition the problem crops up.

1, There is a 'humming noise' from behind the dashboard when the ignition is on - any ideas what this is?
2, The electical power drops, the ignition light goes dim and if I try to turn the engine, it either does nothing or clicks.
3, If I then switch ignition on the light sometimes begins to glow, but the car still wouldn't turn over.
4, After a few hours it seems to fix itself and all is OK - until the next time.

My guess is ignition switch, it's pretty rough and either is stiff or very loose, without a wiring diagram it is hard to work out if this is possible.

Cheers

Rob

first check the battery to chassis to engine earths.

The electrical manuals are in the Rave workshop manual which you can download off the Internet. It's a big file so give it some time.

The white wire (anywhere) is switched ignition and should be 12.5v or so without the vehicle running but with the ignition switched on. Measure the voltage on this and then measure the battery voltage across the terminal posts at the same time. They should be the same value if not Then either it's an earthing / ignition switch / connector / fuse issue. With the ignition on measure the voltage between the -ve battery post and the bulkhead, this should read 0 volts, if not it's an eathing fault for sure.

If the earthing is a problem check these earthing points. a) near battery, b) bulkhead near starter motor, c) near dash.

To check the ignition switch take off the column cowl and with the ignition off check the voltage feed to the switch (only one wire will be 'live'). Switch on the ignition and measure the same wire, if the voltage in is OK (>12v) and the white wire is below 12v then the switch is screwed.

Simples

Change the battery.

Sounds like a problem I had with my 1985 90 just prior to it's last MOT.
I went to turn the engine on and it just clicked.

First of all, I was thinking battery because I'd been having problems with it going flat for a while anyway so I got a brand new Numax and it was duly installed but no change.

Click, click...

Holding the ignition key in the starter position with a brand new battery had a slightly unexpected effect - a burning smell and a cabin full of smoke.

Time to call the AA.

I'd heard stories about the clicking thing in the past being related to the starter motor solenoid sticking and that if you hit it with something heavy to free it, that would normally start working (it certainly did in an early 1990's cavalier we once had).

Breakdown man arrived and was stumped. I offered him a spare starter motor / solenoid that I had in the garage to swap over but he said that it would take too long on a 200tdi and it's not the sort of repair that they do.

So, breakdown man went away and got a flat-loader and it was off to Challenger 4x4 in Tongham for the beast!

Some days later, I was advised that all my wiring was knackered and had to be replaced as somehow a short was causing 12v to go to earth via one of the thin ignition wires which had melted and was completely fried.

Ended up costing me several hundred pounds in labour but at least the beast was back on the road.

Gidgrace, dodgy earth.