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The red lights at the bottom of most VDO tachs that we have in our Speedsters are warning lights. The left one is alternator/generator output which in a VW Type 1 engine could mean your fan belt has come off which is bad, bad, bad, The right light warns of low oil pressure. Both should illuminate when the ignition key is turned on and then go off and stay off once the engine starts.  Does the light come on when your engine is at idle? If so you possibly have a low oil pressure issue. Could be a sign of a worn out engine among other things. 

Well, first we have to make sure we know the function of that right side light in the tachometer.  On my car, right is for the alternator and the LEFT side is for oil pressure.

If it is the alternator light coming on like that, I would suspect a loose fan belt or a loose wire going to the alternator.  Check both wires, clean up the connections with light sandpaper and tighten.  Check the fan belt for no more than 3/4" deflection when pushing horizontally halfway up the left side.

If it's the oil pressure light coming on, then there's either a loose connection on the pressure sender or else something funky's going on elsewhere.

First, though.....   Determine whether it is an alternator or oil light.

^^That^^

It could also be that your idle is a tad too low.  Check to see if it idles at about 800 rpm and if it's low, bring the idle screws up 1/4 turn on each side (try to keep them even) til it gets to 800.

On top of the alternator are two wires, one big and one small.  Remove the small one and place it aside so it can't touch anything and is away from the fan belt.  Go start your car.  One of the tach lights will remain on all the time.  That one is the alternator light, the other one is oil pressure.  Once you know which is which, we can offer better advice.  Don't forget to re-connect the alternator wire!

Last edited by Gordon Nichols

Do you have an alternator or the older (originally more popular) generator?  Generators needed near 1500 rpms to charge while a alternator charged at idle (950ish).  Both have regulators that can fail.  Some later alternator have internal regulator - other have external.  Again corrosion can add unwanted resistance.

The oil pressure switch is generally attached to a T (or dual sender) under where the distributor is.  You could turn key to accessory so tach lights are on and pull the connector from that oil pressure sensor - light go out then its for oil pressure.

Many add extra gauges so they better know the condition of the engine oil pressure and temp, amp/volt meter.

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