hi Circa,
You cannot connect an LED chain, without a series current limiting resistor, directly to your vehicle battery. They will most likely burnt out.
The usual way for strings, is to calculate the series resistor assuming, the highest possible battery voltage that will not exceed the LED's current rating.
To chose the number of LED's in the string, assume the lowest battery voltage that will exceed the total voltage drop across the LED string.
eg: say the battery minimum is 11V and the LED Vfwd is 1.6V = 6.8 LED's so use 6 LED's in the string =9.6Vdrop.
Next to ensure that the 60mA LED rating is not exceeded when the battery is say 14.4V, would require a series resistor of [14.4v-9.6v]/0.06 = 80R
At the lower battery voltage of 11V, the LED current would be 1.4V/80 = 17.5mA.
A way to overcome this change in LED current would be to use a 60mA constant current source.... OK.?