# 5 fuse blowing

[dsw99a]

Hiya folks. I have a fuse blowing issue on a 1987 528e.
Electrical is not my favorite- but, ive opened up and cleaned the light switch. Really gunky and nasty. 
Ive now blown all my white fuses to check this issue at the moment.

Here is what i was trying so i could isolate the issue; this fuse (#5 white fuse 8 amps) covers the park-sidemarker-a taillight n.,rear foglight, instru. a. license plate illumination

the left blinker works(front and back), but the park marker lights dont work(front or back).

addendum- I had and am having problems with my speedometer(2nd time changing gears still erratic.) I did the battery renewal, it showed well for about a week so i think i have to resolder the contacts.

i unhooked the license plate lights, took out bulb at left rear marker and took out bulb at left side marker and front blinker/park light bulb also.
So in (my) theory- when i get some fuses i should be able in install and turn on switch without it blowing, and then one by one plug each bulb in to see when the fuse burns out? 
does that make sense? if not how can i trouble shoot this issue? i do have a multimeter, just dont know how to use it well.

thanks in adavance.

d.wil

[Aldo525]

There are others circuits related to #5 fuse:



Removing the bulbs won't necessarily reveal the source of the problem; that is more likely related to the wiring or connectors in the fuse #5 circuit.
You need to look for loose or damaged wires... the glove box switch wiring is a common culprit, but you should check all the relevant wiring.
 

[Driver72]

When does it blow?  Turning on lights? Or something else.  I kept blowing that fuse due to a lock actuator that was struggling to unlock a sticky lock mechanism.  

That lock would immediately draw a ton of power when it hit the resistance.  

gas cap actuator was sticky too.   

[dsw99a]

the fuse blows only when turning on light switch.

i have been having problems with obc also.

is there a better way to narrow down what to check/search?

[Shawn D.]

is there a better way to narrow down what to check/search?

By "better," do you mean easier and/or quicker?  If so, going through circuits individually isn't either,  but it's a fundamental way to do it.  At least you can start with the light switch. 

It's time to learn how to use the multimeter to check for continuity and isolation. 

[4DSC]

You could start by checking for a short in the wiring to the different light circuits to isolate if one of them is the cause. Unplug each light connector with the car off and connect multimeter between each power pin and the ground pin. If any of these tests show continuity, that particular wiring has a short somewhere. At least that makes sense in my mind, but I'm not an electrician.

[dsw99a]

by "better", i meant "more efficient".
If anyone can give me a foolproof method to go about systematically testing these circuits-please share. Asked the fool

Am i in the ballpark when i assume that it must be some function of the light switch, being that the fuse only blows with the switch activated?
With that-shouldnt i have to test only those wires?

[Dana in Reno]

It's almost certain to be something connected to the switch, but not necessarily the switch itself.  The best place to start is to test each light unit for shorts the way a previous poster suggested.  The tail light clusters are a likely source due to the potential for water intrusion, so you might begin there.