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?

[QBee]

My only concern is that you have some sort of fault and the fuse is doing its job, and putting in a bigger fuse might give you more problems of an electrical nature.
Of course, the ultimate electrical problem in a glass fibre car is fire.....

[Pothole]

intermittent short somewhere? Do the brake light wires rub anywhere?

[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

[QBee]

Share your frustration Dr Mike, especially as fuses aren't free on the NHS.....

I cannot answer your request for information, but can just observe that I use my 1999 car all year round. 12,000 miles a year and in all weathers and have not had this happen, and it's also not something that you read about on PH.....ever, as far as i am aware.

I too think you have a wire shorting, and it's a case of working out what is shorting it and tracing the wiring. You seem to think it is the wipers parking that is causing the issue, so that would be the place to start looking.

Bloody stupid fusing two such disparate things together.....

[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.

[spend]

Sounds reasonable... except it probably takes @40A to blow a 20A fuse ~ which makes it a little more worrying.. Fuses aren't great protection for the wiring and can quite often still allow melting insulation on the wiring (personally I always consider using cable 2x the fuse rating as a target).

You could put separate fuses on brake & wiper circuits to test which is the root cause, but that means hacking looms etc.

If you insist on using a larger fuse rating, I'd consider the expense of a circuit breaker (they react faster & of course you only have to press them to reset).

TBH I'd say it is quite possibly as simple a case as your wiper motor getting marginal for the load on the wipers?

[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.

[nawarne]

Dr Mike Oxgreen said:

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.

I might also hazard that a tired motor is starting to draw more current.

I too would be wary of increasing the fuse rating.

Have you applied contact spray/checked the spade connectors to the motor and park switch? Sometimes a bit of crap/oxidisation on the connectors can be just enough to increase resistance such that the current draw is more. Had an issue on my car where the main beam fuse would blow intermittently - sometime I'd have main beam then the 2nd or 3rd time I used it, the fuse would pop. In the end I sprayed the contacts on the fuse board...and no more problems.

I guess that the footwell tends to get a bit damp and on a low usage circuit you might get a build up of oxide?
Nick

[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.