Overdrive fuse?

My '66 S has an overdrive that does not switch on but the dash light illuminates when switched. The previous owner replaced the solenoid with no success. I have not been under yet to test for power but I wanted to check for other faults first as there is no tell-tale click from underneath when switched. The wiring diagram shows an in-line fuse, but I cannot find it. Does anyone know where this fuse is in the circuit? I assumed it would be readily accessible behind the fascia but one never knows. There are a few other in-line fuses noted on the circuit diagram and I wonder where they might be, but I haven’t had a need to check yet.


As a preliminary test I would find the bullet connector at the solenoid and connect a test light to this and to ground. Then turn on ignition, engage forth gear switch overdrive lever to ON and see if you get power at the bullet connector. If no, then restart your search for the inline fuse. Keep in mind adjustment of overdrive solenoids is critical. The solenoid contains two coils, a pull in coil and a hold in coil. Initial switching on energizes the pull in coil (on my 3.8S this draws about 15 amps per the dash ammeter), then once solenoid has moved to full travel the pull in coil disengages and only the hold in coil is in operation drawing much less amperage. IF the adjustment is incorrect the pull in coil will operate continually and the result is it will burn out in a relatively short time likely blowing the fuse.

On my MK2 I follow the wire back to where it connects to the overdrive box and the fuse is almost into the area where the stick shift sets. It will be very greasy and a good cleaning will fix it up. The fuse is NOT behind the facia,. Could Jaguar have made this more difficult…

I also do not try to engage the overdrive for at least five minutes of driving as the oil is very thick and the solenoid has to fight against that and it usually won’t even go into OD.


I would run a live wire to the solenoid first to test it , will fire in with a click if all ok .

On all the other tests , make sure gearbox is in 4th , overdrive selected , and ignition on , of course .

Thanks everyone for your advice and experiences. I have not had the car long and am still sorting out a list of electrical/electronic matters. When the O/D is switched on, there is no showing on the ammeter so I assume there is no power to the solenoid, or it has an open circuit. When I get a chance to get back to it, I’ll check for power to the feed at the solenoid end first and go from there. I believe it is not easy for the home mechanic to ‘bench test’ the solenoid.

Far from the truth , just put the body on one battery terminal and the wire on the other , it will fire in if working !
Ps don’t hold the wire on the terminal for too long , just a second or 2 , if it’s good it will work straight away !

Not so simple for these solenoids, Ian. They are a double coil with internal switch. Both coils are used to drive the plunger to shove the lever over to engage as it needs some grunt, but this mode simultaneously nudges the power switch to cut off the closing coil power, leaving power only to the ‘hold’ coil. The warning in the manual states -
"The solenoid should never be bench tested as, when the solenoid plunger is not loaded the impact of the plunger will tend to bend the contact arm thus preventing the points from opening".

This means it would be a simple job to write off a solenoid. It should be possible to do a bench test provided the unit were held in a jig to replicate the stroke limits, and in conjunction with an ammeter to check for high and low loads. I assume a damaged unit like this would draw maximum load constantly - 20 amps in the book - and would burn out fairly quickly. I’ll get to carry out the usual tests when other jobs are out of the way.