Lifetime Premium Member
Date registered: Oct 2002
Vehicle: 1967 250 SL, 1963 220Sb
Location: Los Angeles / Altadena
Mentioned: 3 Post(s)
Quoted: 102 Post(s)
As best as I understand it, the clicking is the solenoid trying to engage but for whatever reason not being able to. This could be because it is stuck (unlikely) or because it is not getting sufficient power, or it is poorly grounded. Measure the voltage across your battery terminals when not trying this - it should be something like 13.2 volts. Then measure it when you are trying to start the car. If it drops down to 10 or something it's battery. With your jumper cables, is your jumper car running at the time? Again, measure the voltage.
You mention that the car hasn't been driven in 20 years. Does that mean the battery is 20 years old? Even with a jump start I doubt very much that you are going to get anything to work prior to replacing the battery. A 20 year old battery is a liability - remove it and put in a new one if that is what the situation is. I got a 1 year old AAA battery at the junkyard for $35 recently for my fintail. And I bought a $140 Bosch for my other car. Hint: best deal on Bosch batteries is buy on-line at pepboys and use the coupon code to get 20% off. Then pickup in store.
I spent a LONG time trying to figure out a similar problem on a 1966 Alfa 2600 before finding out that the battery voltage was low by about 1 volt. New battery solved the problem.
Currently: 1967 250 SL, 1963 220Sb, 1965 300SE Lang, 1971 280SE parts car, 1972 Alfa GTV, 1965 Alfa Duetto, 1993 BMW R100R
Past: 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...