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Failing Wipac Style Lamps

Repair Guide Failing Wipac Style Lamps

I have just repaired two Lamp Holders that failed in an identical way so I wanted to find out why they failed to prevent any more going the same way.

One was a Tail light and one was an indicator, - so what was the problem?

There are several issues which lead to corrosion and failure. Both units failed when the Earth contact attached to the side spring simply fell off. On both units it was the rivet that held the ring terminal crimp to the bronze strip corroded to dust.

Also on both units it was the panel screw holding the bronze strip that had rusted to the point of also causing a bad earth to the bodywork.

The problem is the classic case of dissimilar metals causing corrosion of the more active metal in the galvanic cell. This is now made worse because we are actively pushing a current through it!

The rivet on the bronze strip seemed to be made of an alloy - and possibly even aluminium, and it was into a tinned brass ring terminal. So galvanic sandwich here is bronze, aluminium, tin, brass. There is also a nice crevice to hold an electrolyte - probably Stannous (Tin) chloride from the action of the tin plated connector and salt water.

The other side isn't any better either, as the steel screw is zinc plated, is in contact with the bronze strip, passes through the PVC space of the cover - which collects water, and into the aluminium panel. So the galvanic cell is Bronze, Zinc, Iron, Zinc, Aluminium. The largest potential difference is between the bronze strip and the zinc plating under the screw head - so this essential electrical contact corrodes first! After that the rest of the screw looses it's zinc plating but it starts under the screw head first, and in the case of the front lights in the wings, the exposed end of the screws.

Many of these lights seem to have the drain gap in the PVC boot in the wrong place also, so it ends up at the side. This allows the assembly to fill up with water and start the process.

Here is my solution:

If you buy a light - check the rivet connection at the back to see if it is bronze or an alloy. If it is a light colour then file it off and use a 9.5mm Spade crimp terminal instead. The Brass non-insulated type are best and will crimp to the wire well and fit the bronze strip. Use a dielectric grease or vaseline on the end of the wire and strip then push on for a firm connection. The galvanic cell has now disappeared, as the metals are Bronze, Brass, Copper, and the grease will keep the joint free of electrolyte.

For the body screws -go to stainless Steel. These do not have a sacrificial coating, but the steel will not corrode when in contact with the bronze, so this contact should remain good even when wet. BUT at the other end where stainless steel goes through aluminium this is now a more serious problem. This is acceptable within the industry because the surface area of the aluminium is much larger than the stainless steel fixing. What can be improved is keeping the water out of the joint by using dinitrol or other heavy bitumen type rustproofer on the back of the panel fixings, or just on the screw itself when you assemble it.

The bulb base itself can corrode in contact with that bronze strip, but just a smear of dielectric grease on the strip 'finger' should cure this.

The last thing is to make sure there is a drain gap at the base of the black plastic by cutting a slot that goes through to the white plastic base, or turning the outer cover to align the slot with the base and make new holes with screws at the back when you install it.

The connectors to the loom should also have a grease like vaseline to keep them corrosion free, and if they look dull - give them a polish with scotchbrite first.

Hopefully this should keep your lights burning brighter for longer!

Please add your experiences with failed lights to see if we can prevent this.

Latest reviews

Excellent; concise , deals with a real issue with enough of the science included to give confidence in the cure. Ill be revisiting some of my lighting.
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