[TR] A type overdrive solenoid problem?

[Bud Rolofson]

The OD on my TR6 stopped working so I did the trouble shooting process  
in Dan Master's electrical manual and found I have voltage all through  
the circuit all the way to the bullet that connects the (yellow with  
purple stripe) wire to the solenoid. The voltage can be switched on  
and off with the OD selector switch on the column so everything works  
up to the point where it connects to the solenoid. But the solenoid  
doesn't engage.

So the solenoid is bad right? What has me stumped is that the solenoid  
will operate if I hook it directly to an extra battery that I have.  
Why would it work with 12 volts directly but not 12 volts through the  
circuit? I even swapped out another solenoid from another A type OD  
and that one does exactly the same thing. Works with a direct hookup  
to a battery but not with the circuit. I checked to see if the  
solenoid is grounded and it has continuity according to my meter.

With the solenoid hooked to the system when I engage the OD switch the  
voltage goes as far as the bullet but doesn't register at the  
solenoid. It's as if the solenoid "clogs" the flow of the voltage.

What could be causing the solenoids to work with a direct battery  
(voltage measured at 12.11) but not with the circuit (voltage measured  
at 12.75)?

I'm stumped. How can both solenoids work in one situation and not the  
other?

Thanks
Bud Rolofson

71TR6 CC57365 (Good 6)
71 Spitfire MK IV Race Car #3
66TR4A CTC57529 (The Project)
71F-250 Camper Special (Triumph Support Vehicle)
Z-50A Hardly Davidson 1977 Honda Mini-Trail Bike (Triumph Pit Bike)