Light less-than-fantastic!

[willum]

The wierdest thing! My W124 300D Estate went in for the back box and an MOT.
Whilst waiting for the box the battery went flat. Recharged, car fine, left 2 days, flat again. Recharged. Altenator outputs at 13.5+ volts, fast idle, battery discharge test good.
Runs/drives fine but if revs drop below 1000, charge light glimmers and ALL repeat ALL the bottom row of warning lights come on. When the battery is disconnected it sparks so something is going to earth (yes, all the auxilliarys are OFF).
My thoughts were a diode in the altenator rectifier but how is it putting ALL the warning lights on.
Is this possibly an OVP relay fault and............
What is the famous - or infamous - OVP relay and should I be looking at it??

 

[jibcl500]

Sounds like the diode pack on the alternator,

jib

 

[television]

The diode pack as JIB says must be the first port of call

The OVP relay could not give this fault

 

[willum]

Thanks for the quick replies, folks.

Still a bit bemused as to why the altenator going downhill should produce a fault like ALL the bottom row of dashboard warning lamps coming on.......... and I'll stop blaming that innocent OVP relay.

What is it anyway??

Is there an explanation on the site anywhere?

 

[television]

Thanks for the quick replies, folks.

Still a bit bemused as to why the altenator going downhill should produce a fault like ALL the bottom row of dashboard warning lamps coming on.......... and I'll stop blaming that innocent OVP relay.

What is it anyway??

Is there an explanation on the site anywhere?

I must have written this out out 500 times. the OVP relay is there to protect the expensive ECU's from damage should a fault happen in the charging system of if the battery was overcharged or fitted incorrectly. it has its own fuse and has 2 x 7.5volt zener diodes. If the sensing circuit goes wrong on the alternator and the voltage rose too high, the holding zeners will allow the fuse to blow reducing the output to the ECU's down to 7.5 volt, the output is always on pins 87 that should have 121 volt on them.

Many were dry jointed from new and the Austrian ones were the worst, the Irish were quite good. Many just solder the up

 

[willum]

501, now

Thanks, television