Club Triumph

I have a problem with the headlamps not raising with the light switch. When I switch the lights on the relay that raises and lowers the headlamps buzzes but doesnt operate, so the headlamps stay down. If I turn the lights off but then operate the flash the headlamps raise and pause before lowering again as normal. If I then switch the headlamps on while the headlamps are still raised from the flash they stay up.

I read a post that said someone with the same issue found a blown diode in the pektron unit, so I removed mine and unsoldered the diodes that are in circuit so I could test them all. My multimeter has a diode test function which shows approximately the right voltage drop in one direction and open circuit in the other so I think all the diodes are working.

I thought maybe there was a bad connection somewhere that might mean no enough voltage was available for the relay to close from the light switch so I took out relevant fuses to clean the contacts up but this was when I noticed something odd that I have been poring over the circuit diagrams trying to figure out without success. If I remove the fuse for the left side side and rear lights the headlamps operate normally with no buzzing from the relay, put the fuse back and it starts buzzing and failing to operate the headlamp motors again.  The side lights don't look to form part of the circuit that goes to either the pektron unit or the relay itself so I can't explain the behaviour. The only thing I can think of is that the relay is dodgy and taking that fuse out somehow gives just enough extra voltage or current to allow the relay to work so I am going to get a replacement relay and try it but in the meantime I wondered if anyone else has come across this issue or understands the system well enough to know what might be happening to shed any light on this issue?

I really thought it was going to be a blown dioide in the pektron unit!

You have checked and cleaned the fuse connection - have you done the same for all the earthing.  Each headlight wire earths to the body near the front?

To start with I'd do some basic checks;
• check/clean all connectors and earth points that are related to the headlights;
• pull out the headlight switch and clean the inside. They have a habbit of corroding badly, but are easy to clean;
• check wiring for damage, bodge repairs etc.
What year is your car?

Hi Steve,

Thanks for tge suggestion. I didn't get a chance to check any earth's as i ran out of light before I got further.  I will do that if a replacement  relay does similar to the existing one though.  I have seen bad shared earthing points cause all sorts of issues with otherwise unrelated circuits in the past but there is usually logic to it if you look at the circuit diagram but so far I have been unable to do the same on this one.

Quoted from Beans

To start with I'd do some basic checks;
• check/clean all connectors and earth points that are related to the headlights;
• pull out the headlight switch and clean the inside. They have a habbit of corroding badly, but are easy to clean;
• check wiring for damage, bodge repairs etc.
What year is your car?

I don't remember the details of the circuit (it's a good fifteen years since I owned a 7) but if the relay earth is shared with the sidelights (and not properly earthed) it would explain your symptoms. With the fuse removed, the LH side lights are unpowered. Current through the relay winding can flow back up through the front side-light and down the rear one to a good earth. With the fuse in, the top of the front sidelight is powered, so this earth path is not available. When you flash the headlights, the sidelights are not turned on, so the situation is the same as without a fuse.

Quoted from RobPearce

I don't remember the details of the circuit (it's a good fifteen years since I owned a 7) but if the relay earth is shared with the sidelights (and not properly earthed) it would explain your symptoms. With the fuse removed, the LH side lights are unpowered. Current through the relay winding can flow back up through the front side-light and down the rear one to a good earth. With the fuse in, the top of the front sidelight is powered, so this earth path is not available. When you flash the headlights, the sidelights are not turned on, so the situation is the same as without a fuse.

On an 1981 model there's an earth point close to the fusebox, on the inside of the A-post. This is on a LH drive car, so in your case mirror this image ...
Access might be difficult with the dashboard in place though



There are also two earth points under the bonnet directly behind the headlamp panel, just visible on the LH side of the wires. Clean these carefully ...



Never tried removing the wiring plus fuse panel with the dash fitted. This clearly shows why I think  

Yep that's pretty conclusive that it's not possible to get at the relay/fuse panel properly without removing the dash. I think 😁

That earth does look like its likely to be involved.  Particularly if the dash lights use it too. I was hoping to put off dash removal til the summer (I have a slight smell of anti freeze and damp tunnel carpets so I think the matrix or its seals must have a leak). Depends if the garage that does my MOT's will pass it on the basis that the lights do work, albeit with  an unusual procedure. Mot is due Dec 14 so if they won't I'll have to  brave the cold as my garage is too small to work in and besides its full of a half restored Stag.

Thanks for the info, very helpful.

For the MOT you can always disconnect the headlamps motors and raise them manually before you drive to the MOT station.
At least that is allowed over here, as long as the lights work when you switch them on ...

Interesting development, I switched the dash lights off using the dimmer rheostat, headlights worked perfectly, switch them back on relay buzzes and headlamps don't lift. I am fairly convinced its a shared earth now, probably shared between the pektron unit and the dash lights. This weekends job will be to go hunting for the earth for the dash lights.