Wiper park fuse blows occasionally

[Dr Mike Oxgreen]

Approximately every six months or so, the wiper park fuse fails on my '99 Chimaera. This is more than irritating, because as well as meaning that the wipers don't park properly the fuse is also shared with the brake lights so it leaves me with no brake lights.

If I remember correctly it's a 20A fuse. The fact that it blows so infrequently leads me to suspect that there's no real problem, but maybe the fuse is close to its rated load and hence vulnerable to blowing - perhaps the filament weakens over time.

I'm considering replacing it with a very slightly higher fuse - say, 25A - in the hope that it still provides adequate protection but won't be as vulnerable to spurious failure every 6 months or so.

What do you think?

[Dr Mike Oxgreen]

If the fuse were blowing every few weeks, I could believe that it's an intermittent fault. But the fact that the fuse blows so rarely - at least six months or more - just makes it feel like there's some other explanation.

I'm musing that perhaps TVR specced a fuse for that circuit that is only just big enough for the job. Let's imagine that when the wipers are parking and you use the brakes this gives a load of 18A - would a 20A fuse gradually weaken over time in that scenario?

I've got LED stop/tail lights, but I think they've got load resistors in them so that they work with modern cars that detect failed bulbs. Hence, the load is probably the same as a conventional bulb. Oh, and I have only recently fitted these and the problem existed before, so these bulbs are not the culprits (at least, not on their own).

Does anyone know what the wiper current draw is at normal speed? With that information, plus a pair of 21W brake light bulbs, we could work out whether there is sufficient excess capacity in a 20A fuse to avoid spurious failures.

For now, I've bunged another 20A fuse in to replace it. But I just know it's "only" going to last six months or so.

Edited by Dr Mike Oxgreen on Wednesday 20th August 13:00

[Dr Mike Oxgreen]

Yes, I guess you're right - if the fuse were under-rated then you'd hear more people reporting the problem.

Oh well, perhaps it's just one of those niggles that I have to put up with.

[Dr Mike Oxgreen]

Interesting stuff. So would a tired motor draw more current than a new one?

At least both the wiper park and brake circuits are loads that are typically only on for a few seconds at a time, so probably not going to see too much heat build-up.

[Dr Mike Oxgreen]

Low usage... You may have a point there: this summer has been quite good.

I'll have a hunt for the wiper motor connectors, though everything is pretty difficult to reach on the later wiper motors above the driver's knees (as distinct from the ones in the corner of the engine bay, which have their own issues with water ingress). I'm sure I've got a tube of dielectric grease somewhere, which might also help.