[Mgs] slow, hungry wiper motor

[Paul Hunt]

Probably a slightly bad connection in the ignition switch, or the white or 
brown circuits either side of it or to the alternator, or indeed a blown 
(open-circuit) alternator diode, the light can glow brighter the more 
electrical things you have switched on, and is more noticeable at night of 
course.

The ignition warning light acts as a balance scale - as long as it has the 
same voltage both sides it will be dark.  This can be zero volts i.e. when 
the ignition is off and the engine is stopped, or around 14.5v i.e. when the 
engine is running and the alternator is working as it should.  These 
voltages are sensed on the white coming off the ignition switch, and the 
brown/yellow coming off the alternator, if one is higher or lower than the 
other the light will start to glow.

When this is happening measure the voltage on the white circuit (which needs 
to be at the ignition switch or ignition relay depending on year and 
market), the brown at the alternator, and the brown/yellow at the 
alternator.  If you get a potential different between the white and the 
brown the problem is bad connections from the alternator down to the 
solenoid, and back up to and through the ignition switch or relay.  But if 
those two are much the same and it is the brown/yellow that is higher or 
lower than the others, then it is an alternator problem.

Slow wipers can indicate problems in all sorts of areas, like bad 
connections anywhere in the brown, white or green circuits, but also 
mechanical problems in the motor, rack and pinion, or wiper wheelboxes.  The 
problem with wipers is that bad connections will cause low voltage at the 
motor, which causes slow speed, which causes higher current than normal, 
whereas mechanical problems cause high current, which causes lower voltages 
than normal.  Which, can be difficult to determine.  However purely 
mechanical problems shouldn't cause the ignition warning light to glow, if 
the electrical connections are good.  But then you could have both!

PaulH.



----- Original Message ----- 

> Driving home last night, I saw a very faint glow in the ignition warning
> light.  It was raining, it was dark, and I had the radio on.  I have a
> decently sized alternator, so this is not a situation where I normally 
> think I
> would be overloading it.
>
> After a few miles of travel, I determined the glow went away when I turned 
> off
> the wipers, which have been a bit sluggish anyway.