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1974 Jensen INterceptor electrical help needed


Freshman Member
I am new to british cars and this website.......I am in Atlanta Georgia USA, and recently purchased a beautiful 2 owner Interceptor convertible, original paint 20,000 miles from Calif from a long time family friend.

I have rebuilt a few things like the steering rack and the carb and tuned it up.

Electrical issues abound though, like none of the 4 power windows work, the front side marker lights do not work, the 3 interior courtesy light do not come on, the flexible under bonnet light does not work, the horns do not work, the radio aerial does not go up or down, but radio comes on, the ac compressor does not cycle and the front passenger side headlight and brights do not work, left sides does come on. I have checked many fuses, changed many bulbs and no good results............I have a wiring diagram and chassis manual, but I'm not really an electrical genius. All thoughts are appreciated. Mark


Country flag
If you don't have a continuity tester and a test light, and perhaps a multimeter, or don't know how to use them, to save time, aggravation and maybe a fire or two, take the car to a skilled and experienced auto technician and pay him to trace out all circuits.


Staff member
Country flag
Mark, welcome!!! Glad you are here and I am only a little envious of your car - and we very much need pictures!

I can't tell you much about the marque specifically but, can tell you a few things generally.

1. If you don't have them, go get a continuity tester and a meter from Harbor Freight (or elsewhere cheap)

1. 90 plus percent of the time electrical problems are issues with grounds. Ground wires are black - find every end you can and clean and re-attach.

2. Check your fuse box - confirm that the fuses work with the continuity tester NOT sight as often the wires break under the cap. While you are at it, check the metal clips the fuses rest in, the rivets loosen over time.

3. Wiring does not require a genius - just the ability to trace wires and the time to understand colours - Take your manual to Staples and get the wiring diagram blown up as big as you can on the photocopier, buy some markers and start colouring. (seriously) British wiring is standard - so, for instance, almost all your niggles will be (likely) related to green wires - or green+ something else (12 V - ignition on)

4. Your horn should be a purple wire - but, there especially, most likely a ground - the ground BTW will be at the horn not the horn push.

5. One thing (circuit) at a time - your manual should tell you what circuits feed what ancillaries - so, you should be able to narrow it down.

6. If I can do it, anyone can - go slow and methodically and you should be fine.

Keep us posted and feel free to ask specific questions.

good luck!


Obi Wan
Country flag
Certainly best to do the diagnosis yourself. A wiring diagram and test meter and time is all that's required. Sending it to a professional to track down wiring problems can get really expensive as it can be really time consuming. Going shop rates are $100/hour or more these days. Oh, forgot to add, I'm also envious of your car.


Freshman Member
Thanks for the comments..........we shall see tomorrow as I am taking the car to a good ol boy in Cumming, GA for him to try some of these things. I did get the passenger side headlights to work though............not really sure what I did but I took the headlights out and started cleaning and voila!!!!!!!!!!!!!!


Great Pumpkin
Mark - that's the first thing to do with non-working lights. Test the bulb to see if it's burned out, then clean all the contacts in the socket (and check for blown fuse and loose wires).

And there are several good ways of cleaning those contacts.

One step forward!

Tom M.


Jedi Trainee
I second what JP said. I have had tons of bad ground issues with my Spitfire Sabrina. Makes me believe the car spent a lot of time at the ocean.
Had similar issues with marker lights and turn signals. Emergency flashers were always a problem until I took emery cloth to the fuse box terminals.
I also am envious of your car. Want to trade it for a Horch? Just kidding. Good luck.


Freshman Member
Ok so I drove the car for the first time ever after much detailing and rack and carb rebuild ,to the guy who is working on the few electrical issues. Fun car and fairly fast.


Freshman Member
I also had replaced the front end bushings and all rubber components and the rear shackle bushings..................Really alot of fun to drive even with just 8.2/1 compression........I thought i'd be a dog..........

Are the front red side marker lights supposed to be on when the headlights are on? They are not now but maybe after the local guy tries.........we shall see.
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