HALOGEN REVERSE-LIGHT CONVERSION & SUCH

Saab uses the same reverse light bulbs as almost all other cars; P21W-BA15s.
The reverse lights on the combi coupe are fairly OK, but I still wanted more white light behind my Saab.
There are several ways to do this.
- Install flood/work-lamps on/under the bumper.
- Modify the reverse light bulb socket, to accomodate a different bulb.
- Make an adaptor, to accomodate a different bulb.

Reverse switches in gearboxes are usually designed to take a load of 2 x 21W = 42W. If we intend to put more load on the switch, we need to assist it with a relay. Incidentally, the Saab 99 with automatic transmission has a relay for the reverse lights. The more modern and improved (?) 900 has not. (Production cost, remember?) According to my parts manual, some 99's got reverse lights inside the front indicator/parklight-units, aswell as in the taillights. I dont know which marked received this, for I have never seen it. Upmarked 900's has it. This means an 84W load, so hopefully Saab used a heavy duty switch.

What "different bulb" should we choose? A friend of mine once had a VW Polo, with only one reverse light.
(on the other side was a rear foglight) He made a special bulb, soldering a H2 bulb into the base of a broken P21W-BA15s bulb. 55 W halogen bulbs make a lot of heat (!), as my friend found out one day he got stuck in a snowdrift, and had to do a lot of reversing… After that, the bulb had "repositioned" itself further down in the light unit... But there are other halogen bulbs available.

I decided to make an adaptor, to accomodate a different bulb. It gives the possibility to change a blown bulb, without having to make a new one. (as my friend would have to)
I chose the HMB52 BA9s 20W halogen bulb, part nr: Philips 12025.


BULB ADAPTOR
- Take a standard reverse bulb (P21W-BA15s), breake the glass, and remove all internals.
- Clean it up inside, using a grinding stone on the Minicraft.
- Drill a 1,5 mm hole in the center contact, and cut away most of the tip.
- De-isolate 5-7mm of a 1mm² wire, pull the end through the hole in the center contact, spread the cords and solder it from the outside. (Not with a sissy 25W iron, use a 100W solder gun)

- Take a park light bulb socket (as used by VW Beetle, Mercedes W123, Mercedes W124, BMW, etc) designed for the T4W-BA9s bulb.
- Insert a scrapped bulb, and leave it there until you're finished. (Important)
- Grind metal off the lower end, until it will enter inside the reverse bulb base.
- Drill a 1,5 mm hole in the contact terminal.
- Cut off the terminal, right below the new hole.
- De-isolate 5mm of the wire in the reverse bulb base, pull the end through the hole in the terminal, and solder it.
- Lower the park light socket into the reverse bulb base, while twisting it one way.
- De-isolate a 15 cm length of 1mm² wire, and coil it into the gap between the park light socket and the reverse bulb base.

- Adjust the height of the park light socket, so the filament of the new bulb ends up in the same
place as the old one, and check that it is possible to change a bulb.
- Seal the gap between the park light socket and the reverse bulb base with solder.
- Test it with an Ohm-meter, to see if the internal wire survived the heat. If so, FINISHED!

Grind inside Cut tip flush Solder the tip Grind off edge Drill for the wire
Solder the wire Coil in a piece of wire Alignment check Ohm test Approved!

This solution may not give the ultimate reverse-flood-light, but thanks to the efficiency of halogen bulbs, the light output is increased. The taillights can be left un-altered, and it doesn't require a new wiring harness, or a relay.
A further improvement would be to put a layer of bright aluminium foil on the matte grey reflector.

THE ALUMINIUM FOIL TRICK

Speaking of improvements... After I had finished a set of bulb-adaptors for my friend Finn's m83 saloon, I discovered that these taillights doesn't have a matte grey reflector, like the combi coupe's. The black plastic moulding isn't even painted! Yes, the reflector is BLACK. Hmmm... This one would certainly benefit from the aluminium foil trick. Let's give it a go!

- Unbolt the light cluster from the car. Four 7mm screws in the boot.
- Remove the lense, the bulbs and give it a good wash. The clever part of using the dishwasher brush, is that you get to buy a new one for the dishes. Which you probably needed anyway.
- I used this aluminium foil tape, which a nice plumber gave to me. It has no label, and I have no idea where he bought it.
- Fit suited lengths of alu-foil, and fine-trim with an OLFA knife.

Unbolt Remove lense Kitchen sink treatment Alu-foil tape
Trim Reflector done Bulbs inserted Brighter looks...

MORE POWERFUL BULBS

Take another look at the "bulbs inserted" photo above. You may notice that the reverse-bulb is not a normal P21W-BA15s. No surprize. But it is not the HMB52-BA9s with my homemade adaptor either!
It is the next step in gaining back up illumination: A 35 Watt halogen bulb with a BA15s base. Two versions exist:
- 795 uses a transverse filament.
- 795x uses an axial filament.
Stern Automotive Lighting supplied me samples of these. The amount of light was IMPRESSIVE!

   
P21W vs 795 Alignment check

HALOGEN CONVERSIONS vs HEAT RADIATION
Most taillights and lenses are made of plastics. These do not handle extreme temperatures well. Variations between different car's taillights are large. Some have plastic bulb sockets, some have metal sockets. Saab uses plastic, exept for the foglight bulbs.
The HMB52-BA9s with my homemade adaptor does not produce more heat than the standard P21W bulb. Move up to 35W and things start getting hot. It may cause damage and deformation to taillight clusters and lenses. But then again, it may not. For how long do you normally reverse each time? Ten minutes? Nope. Less than 30 seconds is closer to the truth. I have equipped an m82 99 saloon with the 795-bulb, to see if any damage occurs. Starting in January 2002, and we'll see what happens.