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Fuse size

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Good Morning everyone just finished my wiring to the rear washer and wipe all new setup but confusion

reigns over fuse size because all blogs refer that a wiper is 15 amp a washer is 5-7.5 amp so as the wash/wipe

works of one switch what size fuse do i put in the holder as this makes up to 20 plus amps intotal. 

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I don't know the configuration on your vehicle, but my 1991 110 CSW has the rear wash supplied by a dedicated pump mounted next to the front screen washer pump, on the wash fluid reservoir.  The reversing lights and rear screen wiper are on fuse position 3, which is 15 amps, and the windscreen wiper and washer are both on fuse position 16, which is 5 amps.  My wiring diagram doesn't show them, but I suspect that both wiper motors are supplied through relays.  I do not know why the rear units need a 15 amp fuse and the front only a 5 amp.

I don't know if any of the above will help you but it's what is shown on my vehicle fuse cover.  Best of luck with your installation.


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Hi Troll Hunter

The set up i have is simple i put a second pump motor into the front washer tank to feed the rear window that goes though to wash/wipe switch also new in dash and that works the wiper as well when turned right and the heated rear window has its own original switch. so i just need to know fuse size for the two.

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15A will be fine for wiper and the wash pump. The actual running current for the wiper is only around 5A, but will be more as it starts on a dry screen but this is only for a fraction of a second until it moves. Washer pumps are only a couple of amps, and certainly a lot less than a wiper motor.

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Thanks a lot Simonb it confirms what i was thinking it just leaves me to fine the right size cable from my batteryto my new extra 4 way fuse board i was thinking maybe 27 amp or do i go up to 70 amp for future use as the fuse holder can take 100 amp max


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Here's a guide for cable capacities:

@ 13.8 Volts
American Wire Gauge (AWG)
0-4 ft. 4-7 ft. 7-10 ft. 10-13 ft. 13-16 ft. 16-19 ft. 19-22 ft.
0 – 10 16-ga. 16-ga. 14-ga. 14-ga. 12-ga. 10-ga. 10-ga.
10–15 14-ga. 14-ga. 14-ga. 12-ga. 10-ga. 8-ga. 8-ga.
15-20 12-ga. 12-ga. 12-ga. 12-ga. 10-ga. 8-ga. 8-ga.
20-35 12-ga. 10-ga. 10-ga. 10-ga. 10-ga. 8-ga. 8-ga.
35-50 10-ga. 10-ga. 10-ga. 8-ga. 8-ga. 8-ga. 6 or 4-ga.
50-65 10-ga. 10-ga. 8-ga. 8-ga. 6 or 4-ga. 6 or 4-ga. 4-ga.
65-85 10-ga. 8-ga. 8-ga. 6 or 4-ga. 6 or 4-ga. 4-ga. 4-ga.
85-105 8-ga. 8-ga. 6 or 4-ga. 4-ga. 4-ga. 4-ga. 4-ga.
105-125 8-ga. 8-ga. 6 or 4-ga. 4-ga. 4-ga. 4-ga. 2-ga.
125-150 8-ga. 6 or 4-ga. 4-ga. 4-ga. 2-ga. 2-ga. 2-ga.
150-200 6 or 4-ga. 4-ga. 4-ga. 2-ga. 2-ga. 1/0-ga. 1/0-ga.
200-250 4-ga. 4-ga. 2-ga. 2-ga. 1/0-ga. 1/0-ga. 1/0-ga.
250-300 4-ga. 2-ga. 2-ga. 1/0-ga. 1/0-ga. 1/0-ga. 2/0-ga.

There's certainly nothing wrong in over-sizing the cables.  The important thing to remember is that the fuses are there to protect the cable, so must be rated at a lower capacity than the cable.  Being realistic, what are you possibly going to install that could use the remaining ~70 amp capacity?  By all means put in a cable of sufficient capacity, but you are wasting money as you will need anything from a 10ga. to a 4ga. cable, and I bet that you don't have an odd length hanging around, so you'll have to buy it!

Hope this helps your decision making.



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  • 1 month later...

I happened across a very good application note from Littelfuse this week and thought it worth sharing the link as well as a couple of snippets from it;


(If the link breaks just google "Littelfuse Fuseology")

Snippets worthy of note:


“…a 20A MAXI Fuse experiencing an overload of 100A will open in about 0.5 seconds. At 40A, the same 20A MAXI Fuse would open in about 9 seconds.”



… a fuse with a current rating of 10A is not usually recommended for operation at more than 7.5A in a 25 ̊C ambient

They also have a good one on transients (electrical fault conditions) in automotive applications:


The sorts of spikes and things they show give you some ideas of what the electrical systems in a vehicle need to tolerate.

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