Fuse Value

[rrbfraser]

Adding overhead lights to my 825i and was wondering what size fuse I should use? I'm installing the on/off rocker switch in the over head next to the wiper switch and they have built in fuse holders (factory setup). Any ideas, I'm thinking about 10 Amp. Thank Bob

[CaptDan]

Several things to consider, first the wire and switch you are using to connect everything. The fuse should be rated slightly lower than the wire or switch as you want the fuse to go before the wire or switch burns.

If this old man remembers correctly the formula for amp is watts of the load - divided by the volts of the power supply = the amps. For example mounting 2 100 watt driving lights on a 12 volt vehicle works as follows 200 watts divided by 12 volts = 16.7 amps

[John Deere Nick]

CaptDan is correct. You always want your fuse to be rated lower than the wire/switch. If it is not and something happens it is more likely to burn the wires and fry the switch before the fuse blows out. Sometimes it happens and you never even now it. I have seen the switch smoke and never pop the fuse. Lots of trial and error when I had sound systems in my cars and mounting strobes on fire truck and personal owned cars. You only screw up a few times before your pocket book reminds you how to do it. 10 amp is pretty normal with added fog lights and what not. double check it though. What kind of lights are you going to use? Post some pics when done.

[rrbfraser]

Thanks gentlemen, that works for me. Have a great holiday!

[J Grace]

I went to 15amp fuse with no issues on the overhead switch from the stock 10amp
and have approx. 30 hrs. on the change.

Merry Christmas to all!
J Grace

[CaptDan]

Thanks J, information about what actually works is much better that theory & formulas !

Merry Christmas to you !

Dan

[pahawi]

Have three overhead switches (Wiper + front lights + rear light) with 10 amp fuses in each. If I used all lights + wiper, the wiper fuse burned. I checked the wiring in the upper console and it turned out the dealer, who mounted the lights, had routed the wires wrong. I rerouted it and no problem since.

/Paul

[JwebsterVT]

Pahawi - I am having the same issue, how did you figure out the wires were incorrectly routed, how did you re-route them? thanks, Jeff

[pahawi]

Not sure my English is good enough to explain, but I'll give it a try:

On mine the problem was that the power wire, to the switch on the middle and the right, on the image below, were connected to the wrong side of the fuses. The big red wire is the main + wire, which goes to one side of the fuse on switch #1. Switch #2 has to be powered directly from #1 and #3 directly from #2. Follow the wires on the image and it should make sense.

Hope it helps.

Paul

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