Starting problem after alternator swap

Tried again with freshly-charged battery today - voltage drops to ~5V when I turn the ignition on (not to start position). So there is a major short somewhere. Looks like I'll have to get the wiring diagrams out and trace the cables...

That sounds like a short and a half!

Is there really no smoke/sparks (flames?) coming from somewhere when you turn the key?

Have you tried disconnecting the alternator completely as you suggested?

Station House said:

Disconnecting the alternator and starting will cause no harm - red ignition light will just stay on - good idea to see if the wiring or alternator has a fault

Click to expand...

Well, here's the latest. I disconnected the new alternator entirely to see if the fault was still there. It was. So that eliminates the alternator.

I checked the wiring coming from the battery with the meter. Attached to the positive battery clamp, there is a fat brown cable which I'm assuming goes to the starter, a thinner brown one, a thin black one, and a thin red one (think this is a homebrew one for driving lamps).

The fat brown one is a dead short to ground. So that might explain the battery getting flattened.

If I had to hazard a guess I might say that the starter solenoid is stuck on (maybe fused) and the starter motor is live. I think a new starter may be in order…

(However, I'm not sure why this happened in the first place. Fitting a new starter could just cause it to go the same way. I'm a bit short of ideas about what to investigate.)

I've started a new fred for this: Ignition short? Bad starter? The saga continues as I now know it's nothing to do with the alternator.

Might be a silly question.. but did your alternator have an earth strap on it... that you might have forgotten to put back on...?

It's not difficult to whip the starter motor off and check that a) it's rotating freely, b) that the return spring is not kaput, and c) that the pinion is able to run freely both ways. Often even a little a bit of **** on the shaft will prevent it from working. Clean all the moving parts and then try it off the vehicle using a set of jump leads directly from the battery. If it doesn't give a good kick when it starts to spin, it would appear that it could do with a rewind and refurb.

By the way, I use a 230A/Hr battery!

Hope this helps.

OSD