[Laird Scooby]

Originally Posted by TonyS9

Could well be the rectifier but just to check on the testing..

When you checked the voltage drops was this with a large load, or using the meter continuity?

The best sensitivity is to put the high beam headlights on with the engine running and measure the voltage across the cable.

Originally Posted by NI_Volvo_Nut

The single spade wire on the rear of the alternator controls the dash lights, have you check this is connected and the connection is good?

All the clues needed to work out it's almost certainly the rectifier (subject to confirming by testing out of circuit) are highlighted in a quote of the OPs OP below :

Originally Posted by John Sweeney

Afternoon all, I'd be grateful for any advice on a no-charge problem with the Denso 100A alternator in my 1992 940. I've had a look back through the forums and, having checked everything in the list below, I'm wondering if there is anything else I should consider before taking it to the mechanic.

The problem happened just as I returned from a 800 mile round trip two days before the lockdown. After all those miles through some pretty rough weather running as reliably as ever, at the end of my road the washer fluid level, bulb failure, battery, brake warning, handbrake and ABS lights came on whilst the engine was running and the alternator stopped charging.

I've looked into the following (I don't have much knowledge of auto-electrics so apologies for any confused terms or illogical thoughts):

- Check output voltage on alternator. Fault, 11.5v.

- Check voltage on exciter wire on key position II. Good, 11.5v.

- Check continuity from alternator ground terminal to lead ground point on engine block. Good, no resistance.

- Check continuity from lead ground point to battery negative terminal through all stages. Good, no resistance.

- Check continuity from alternator positive terminal to battery positive terminal. Good, no resistance.

- Check continuity from exciter terminal to alternator ground terminal. Good, no resistance.

- Check voltage drop between alternator positive terminal and battery positive terminal. Good, 0.1 volt.

- Check voltage drop between alternator body and battery negative terminal. Good, 0.2 volt.

- Check voltage drop between engine block and battery negative terminal. Good, 0.1 volt.

- Check continuity via brush terminals in situ through field wiring. Good, no resistance, brushes and field wiring OK.

- Check for magnetism on pulley bolt when on key position II. Good, field windings OK.

- Check bearings and belt. Good, no noise, no play in bearings, belt running as it should.

- Install new brushes and re-test. Still not charging.

- Install new voltage regulator. Now no warning lights on dash, re-test all connections. Still no warning lights so their route to ground is now faulty.
Remove new voltage regulator and test continuity against old one. New Voltage regulator faulty(!) - infinite resistance. Refitted old VR, warning lights now on again so their route to ground through alternator is now fine.

Still to check:

- Old VR might still be faulty - order 2nd new VR and install.

- Ignition switch could cause similar faults - fit new ignition switch and re-test.

Does anyone have any thoughts on what might be wrong? Have I made any bad assumptions? I'm nearly beaten and the mechanic beckons!

John (the OP) has already done all the testing to confirm it's the rectifier but good practice is always to confirm before replacement, just in case. However being sat at a computer miles away i don't have that luxury.