Mercedes: Instrument issues, hazard switch, finding water

Question
My son just purchased a 1984 Mercedes 300D Turbo and the engine runs great but we have a few items we want to look into.

The turn signal sometimes works OK, sometimes the light just stays on without blinking - relay maybe?

The odometer works now but stopped turning previously.  Is this likely a mechanical issue?

And we are finding water in the floorboards in the back seat when it rains.  We'll need to investigate the source of the leak further, but if you have any words of wisdom from your experiences...

We are not very experienced at auto repair except std maintenance, but we're willing to learn.  Is the 123 repair CD a good resource?

Thanks!  

Answer
The turn signals route through the Hazard Switch, try this DIY first.

Cleaning the Hazard Switch
http://www.mercedesshop.com/Wikka/HazardSwitch

How to repair your broken odometer
http://dieselgiant.com/repairyourodometer.htm


RE: finding water in the floorboards of the back seat

The water usually runs downhill to the back and settles in the same are that you describe, from two general sources:
#1. A blocked hood hinge drain just below the spring that holds up the hood, this can rust a hole through into the passenger compartment, look for traces of water under the front floor mats and side kick panels, give the hood hinge spring area a long (2 - 5 minutes) slow spray and watch the floor with a strong light.
.

#2. Leaky windshield seal, remove front floor mats, give the windshield seal a long (15 minutes) slow spray and watch the floor with a strong light.

You may not need to buy a service manual if you join: http://www.mercedesshop.com/shopforum/forumdisplay.php3?f=15

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