AO Silver Member
Join Date: Feb 2005
Location: Auckland, New Zealand
Re: Help with Alfa Sprint Electrical problem
See if you can get a multimeter to help sort out this problem. I did some checks on my 33 to see if my headlights were lousy for electrical reasons, and gained a third of a volt at the headlights by cleaning the fusebox.
Turn the headlights on then make sure the battery is grounded well by measuring the voltage between its negative terminal and the car body.
Make sure the headlights are grounded well in the same manner.
Now measure the battery voltage with the headlights on.
Then measure the voltage across the headlights.
The difference between the battery voltage and the voltage across the headlights represents power being lost in your wiring due to resistance from bad connections, or possibly old and crappy cable.
Another way to see this is to measure the voltage drop between the battery and the lights, by putting one probe on the battery positive terminal and another on the positive terminal of the headlight (i.e. the correct wire in the plug connector on the back of the headlight).
The headlights use a lot of power, so a lot of current is drawn from the battery. If you remember back to highschool, V = IR (Voltage = current x Resistance). Since the current (I) is big, even a small resistance (R) in your wiring will cause a reasonable voltage drop (V). The less voltage that gets to the headlights, the less light they can produce!
So if you measure 12V on your battery but 9V on your headlights, something is seriously wrong. There is a lot of resistance somewhere in the circuit (maybe the fusebox, maybe some plug connector, maybe some grounding point etc), and this resistance is wasting energy by turning it to heat. Your headlights have only 9V left to make light with.
But if you measure 12V on your battery and more than 11V on your headlight, that's good. You can then put the low light output down to Alfa's crappy headlights instead of Alfa's crappy wiring! Condensation might have left dust etc on the reflector and the inside of the lens, reducing your light output.
Originally Posted by 73GTVJim
"PS and you agree with Ben so you must be wrong