Having had several failures with popup motors, and being unable to find decent replacements, I decided to try repairing those I had. Hopefully this will help a few other owners. I hope the text is sufficient, as adding photos has proved beyond my capabilities! I could print and post! There are some useful photos by brinkie and others on the thread 'Pop up control motor unfunctional - is it repairable?, which I have to credit as being my starting point, but hopefully this provides a more comprehensive guide.
Firstly, some general information. Two motors are listed in the parts book, but the only difference is the length of the lead, and they can both be made to fit either side. The way they are mounted means the motor is inverted from one side to the other. The upshot of this is that the crank needs turning through 180 degrees if you change sides, otherwise the lamp goes up when it should be going down and vice-versa. Most amusing!
The lamps are operated through the tall relay in the main box – it’s a double relay, one for each side. The use of a relay enables a small switching current (ie through the dashboard switch), to activate the relay which switches the larger current to the motor (or any other device which draws an appreciable current). To illustrate this, the diodes in the motor on the low current side are rated at 1amp maximum, but the motors are fused at 30amps. The motors draw much less than this, even at start-up, and the fuse is really just to protect against a short, but it makes the point. In fact, I checked the current consumption on a couple of working motors – a fairly clean motor drew about 1.5amps, but a grotty motor drew about 7amps, and these changed very little after cleaning, so that seems to be a good indication of the general condition.
The entire motor unit is encased in a rubber coating, usually black, but on early(?) cars pale and translucent. This is supposed to keep moisture out, but as we will see, it is not entirely effective, especially when we consider these cars are 30+ years old. The motor unit actually consists of the electric motor itself, and a gearbox which also controls the switching for the up/down action. The gearbox is a simple worm and wheel arrangement. The wiring consists of five wires: green (+12v to motor), brown (motor earth), and red, white & blue to the up/down switching.
So, what goes wrong with them? Sometimes it is just light dirt or corrosion, which causes a lamp to stop in an odd place, and might clear with continued running. This can be achieved by disconnecting the multi pin connector and applying +12v to the green wire for a few minutes – be careful not to touch the brown wire or cause any other short. Reconnect the plug and see if the lamp behaves any better – even if it does, it might only be a temporary fix. Sometimes the motor goes completely dead, and even applying power directly to the green wire does not cause any movement. In this case, there is no cure, but hang on to the unit for spares. Other less likely problems are with the relay (only option is to replace it, if you can find one), or with the diodes but these are usually indestructible (type 1N4003, cheap as chips if you need them).
The more common problems can be tackled by opening up the gearbox; essentially either the headlamp stops part up or part down, or there is a grinding of gears and the lamp does not move. The former may be fixed by continual running as above. The latter will require another gearwheel, which will need liberating from an otherwise dead unit as above; in this case, the dead unit can be opened first as a practice run. The motor and gearbox casings are cast aluminium, with a steel cover on the gearbox, and this is what we need to remove to make any repair.
First though, you need to take the entire headlamp unit out of the car. For once, Haynes is reasonably helpful, so I will just summarise. It needs doing with the lamps raised. Disconnect the motor at the socket. On the left, the battery needs removing; on the right, the washer bottle and other bits need at least moving back. Then move the indicator unit out of the way. Remove the trim from the light, then the light and disconnect the bulb. There is a small gas damper, which steadies the light when up or down, and this needs popping off. It may provide some assistance when raising the light, but the motor will be working against it when lowering the light. The rams are readily available, and are worth replacing if weak – very likely! Now remove the bolts holding the entire headlamp mechanism in, and carefully take it out. Undo the crank between the gearbox and the headlamp assembly. The motor/gearbox can now be unbolted for the real work to start.
The steel cover is on the side where the wiring harness comes in, opposite side to the crank. On my practice run with a dead unit, I scraped off the rubber coating from the whole of the steel cover. This is laborious, using a sharp knife, screwdrivers and small pliers to pull bits off, and shows how much corrosion there is on the outside. This exposed the wiring (red, white & blue) to the block on top which houses the diodes – the other side is where the wipers are which switch things up and down. The brown wire goes directly to the cover (earth), and the green wire (+12v) goes directly to the motor. It is very easy to cut through the green wire, so if it is not a totally dead unit already, be prepared with a soldering iron and heat shrink tubing! On subsequent units, I only removed the rubber from around the edge of the cover, so that the rivets were exposed – I also avoided cutting the green wire!
The rivets holding the cover on can either be drilled out, or I preferred to slice the tops off with a slitting disc in a mini-drill. The advantage to the latter approach is that it leaves stumps to locate the cover when reassembling. The cover can be released by gently levering it off with a knife or screwdriver; it will still be attached to the motor by the green wire – or not! Inside will be a paper gasket and a lot of grot. The grot is composed of old grease, rust, aluminium oxide and plastic particles from the gearwheel. If the gear has stripped, there will be a lot of plastic particles, and another gear will be needed from a dead motor. If this is a dead motor, hopefully the gear is ok for use elsewhere. Remove the paper gasket and clean out as much of the crud as possible. A new gasket will need cutting, using the old one as a template. I have made gaskets in the past from stout brown paper, but I had some thicker (0.8mm) gasket paper to hand so used that, without any problems. Either way, it needs careful cutting with nail scissors, and trimming where it abuts the motor. Holes are best put in with leather punch.
Even if the gearwheel is sound, it is worth removing it to clean everything properly. It is held in with a circlip on the other side. My circlip pliers would not go on, so I had to resort to levering it up and off with screwdrivers. Care needed here if you don’t want to be searching around the room for it, and it’s a good idea to wear glasses in case it decides to go via your eye. If you do lose it, hopefully you can salvage a spare from a dead motor. A gentle tap with a hammer should release the gearwheel, but look out for the washers, plain and spring, on both sides, and the O-ring in the casting. Clean everything as far as possible, especially the metal face of the gearwheel, where the wipers in the cover make contact. Any rusty areas will cause the headlamps to stop prematurely either on the way up, or on the way down.
Reassembly is a reversal of the removal procedure, as they say in all the best manuals. The gearwheel (or a replacement) pushes back in, but be wary not to push out the O-ring. The circlip can be fitted by dropping it over the shaft, holding it down with pliers, one jaw either side of the shaft but not gripping, and tapping the handles with a hammer until the circlip seats fully down. I put a smear of thin oil on the metal face to delay further corrosion, and packed some grease into the worm. There are two unused holes in the cover and the casting which can be used to join them, so put holes in the gasket for these as well as those for the rivet stumps. I lightly oiled the new gasket before fitting. Reposition the cover and bolt it together using the spare holes and two M3 x 12mm bolts.
At this point it is worth testing that it works as expected. Connect to the loom on the car and connect the battery. With the bonnet up, the lights won’t work unless the microswitch in the catch is overridden, by depressing it with a screwdriver. The gear will have gone back in, in a random position, so the motor will likely jump into life until it finds the next park position – hold the motor firmly but keep your fingers out of the way of moving bits, ie the crank and the plastic knob on the motor end. It can now be tested by getting a friend to turn the lights on and off. The crank should rotate 180 degrees at a time, if not it will need further cleaning. If all appears ok, seal it up to prevent further ingress of moisture. I used automotive grade silicone sealant, but how that differs from bathroom or kitchen sealant I have no idea. It was labelled as RTV, which I found out stood for Room Temperature Vulcanising, so now you know! How effective it is remains to be seen, but the original rubber sealant wasn’t 100%, and the motors apparently kept working for some time, despite the corrosion. You may have a better idea for resealing the gearbox.
Reattach the motor unit to the headlamp assembly, but don’t fully tighten the crank on the spline, or the other end of the crank in the slotted hole. Now refit the assembly into the car, attach the loom to the motor, and test again keeping your fingers out of the way. The headlight will almost certainly stop in the wrong places. With the headlamp switch set to ‘on’, disconnect the motor, then slacken the crank on the spline and adjust the headlight to its highest position. Tighten, reconnect and try again. Hopefully the lamp now goes up and down, and stops in the correct positions. Now adjust the bolt at the other end of the crank, in the slotted hole, so that when lowered, the lamp housing is flush with the bodywork. This is a bit more hit-and-miss, as it can only be adjusted when the lamp is up, and assessed when it is down. Eventually it all comes together. Finally tighten each end of the crank. Fit the (new?) damper, and reassemble the rest of the headlamp and trim. By now you should have a smoothly working popup headlamp, which should give good service until it fails again… but at least you will know how to fix it next time! Or do the other side while on a roll!
