Weak blower motors

[ThriftyT]

My dual heater C25 has some very weak blower motors.   I pulled them, bench tested on a fresh 6v battery and the spin like crazy.   But in the car, they seem to hardly turn.   Any ideas?  

Edited April 2, 2020 by ThriftyT

[Mark D]

Run another ground wire from the Electric motor mounts to the chassis. 

[Sniper]

Put a meter on the leads with the motor installed and see what your voltage is then, bet you have some dirty connections.

[ThriftyT]

Thanks guys.  Will try both. 

[Dodgeb4ya]

A special heater switch was used on the dual heaters..the resistors on the switches have either red or green bands on the resister porcelain.

Feed wires have to be in good shape and heavy enough grade wire.

Motors serviced ,lubed etc.

Good grounds important as mentioned too.