Alternator troubleshooting

Graham Thackrah gthack at
Mon Jan 27 11:29:21 EST 2003

Hi list,

Had a funny one this weekend. Been trying to trace a fault on my car (89
100 tq), the charging warning light would only come on dimly with the
ignition on and the ABS light would light then go off straight away. When
the car was started the dash guage would read about 9 volts too. Voltage
at the little blue wire off the alt was about 7.2V rather than 12V too.
Checked the connection at the alt, that was fine, checked the single pin
connector just up the loom from the alt that SJM says to check, and that
was fine too. Following the Bentley wiring diagram shows T10h1 as pin 1 of
the yellow 10 pin connector in the engine wiring harness (under the dash
below the fusebox) as the origin of the blue wire on the alt and a power
feed for the ABS, checking that out and I found one of those nasty blue
connectors for splicing off a cable on the 0.5mm input wire to that pin.
Turns out it was feeding my alarm somehow and I suspect drawing a fair bit
due to a short/fault. A bit confused as to why that would have dropped the
voltage at the alt though, as it was still all connected in parallel, but
that's where my electrical knowledge peters out...

I never usually bother using my alarm so took this opportunity to remove
the offending item, it had those blue things everywhere and wasn't
installed very well at all, neither the remote control module or the siren
were attached and were just left to lie loose in the void behind the dash
and scuttle respectively. That sorted it, now the ABS light comes on and
stays on with the ignition and the alt charging light comes on full
brightness. Once started they both go off and I get a good solid 14 odd V
on the dash guage, that made my Saturday:)

Also managed to pull one of my rear calipers and dismantle it (my bike
bottom bracket two pin spanner makes a superb piston winding tool:) and
free up the stuck handbrake mechanism on Sunday afternoon as well - wot a
good weekend, we even had some lovely weather for a change!



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