Hi , new to this forum but have hopes somone will be able to help me with a problem. Recently i installed a diesel engine in a gas car . no problem other than the speedometer reading is being way hi . the problem: the dc generator on the transmission output shaft is making more revolutions than before (with the old engine ) and naturally , the speedometer reads hi. from what i can find , the transmission dc generator puts out from 4 to 20 v dc that drives the speedo head and needle. i tried to reduce the voltage to the head by installing a 25 k (max) variable resistor in line but this did not have any significant effect. How can i reduce the voltage by approx 30% that gets to the needle?
thanks for any suggestions.

 

Are you certain it is voltage and not frequency that makes the signal?

 

the problem is , i do not know exactly how the generator makes the needle move but think it is by magnetic force , more juice ,stronger pull and higher speed reading

 

It's pretty significant to determine the nature of the signal. Frequency is much less variable than a voltage output.

 

you are right , after doing some more digging , it appears that is is the PULSE frequency that makes the needle move ,not the voltage . is there any way to adjust the pulse ?? if not i may have to invent a gear reduction to slow the generator down.