Suggestions tracking electrical short
Hi,
I am away from y G at the moment, but had an intermittent blown fuse #2 which is now continuous and need to track down what is causing it. (1987, 230GE, 460)
According to the manual, Fuse #2 is for the Off-Side right front and rear side lights, dash lighting, interior lighting and door buzzer.
Its a 8A fuse. Each time I put a piece of 2x5A fusewire in place, the interior lights work fine. As soon as I put the side lights on (doors shut, ignition off) the temporary fuse blows, so there is clearly a short/ground somewhere. Maybe a chaffed wire, or water in something. Probably in the lighting circuit, but could be in the dash.
The question is, what is the best way to check where the short circuit is?
I can use a continuity tester. Can I do something like the following:Ignition off. Fuse out.connect to the car side of the fuse connector and then touch to chassis/earth - there should be continuity because that is what is blowing the fuse.
But how to check which line/circuit?
I suppose if I start with the side light bulbs, remove those, see if there is continuity between the live and earth in the socket - if so, this is where the short is.
After that - it gets messy because a lot of what that fuse controls is behind the dash!
Any guidance/suggestions?
Hi, start with the bulbs, try with one removed at a time and see what happens, may even be a dicky bulb. Don't forget the sidelight feed to the trailer socket, these are open to abuse/neglect and can very often cause problems on all sorts of vehicles. Other likley place is the number plate lights ( depending which circuit they are on). My guess is it'll be something simple and you won't need to go ferreting about behind the dash. I've been wrong before mind, and anything is possible, but don't panic yet.
Instead of constantly blowing your fuses :) :), you could be using a multi-meter, setting your dial at the amps meter. Hoping the meter will have a re-setting trip, usually set at 8 amps or 10 amps maximum.
Given, the safety is set at 10 amps or so, the maximum load of any circuit you are to test is 10 amps. So, you can test light consumable circuits without problems, but do not use this test to diagnose heavy duty circuits such as charging and starting circuits.
Take care to use the meter, once amps has been selected to connect the meter in series only, connecting in parallel as like using it as a volt meter will blow the meter. To elaborate on that, disconnect the negative terminal of your battery, connect the amps meter with the red lead to the negative post and the black lead to the disconnected, negative strap. This is connection in series. Ensure all electrical consumables are turned off before connecting the amps meter.
If you have a clock fitted to the vehicle, then expect a small draw of current due to it. If the amps meter needle reads the wrong way, swop the connection leads to the battery and disconnected strap.
Alternatively, using crocodile clips, remove your fuse and make connection at each end of the fuse terminal end, you amps meter. If the needle reads the wrong way, swop the connections around on the fuse terminals. You can find out which item is the source of short circuit by turning it on, one by one.
You have mentioned that when the side lights are on and the doors shut, blows the fuse, doing that will trip the safety switch. My experience is that the number plate light can be cause of such faults, particularly if the lights have been bashed about, bent over. I would turn my attention to those immediately. If the meter trips, remove the number plate bulb(s) (one at a time) and re-set the meter and try again. If the meter does not trip, you have located your problem, then examine the circuitry of the number plate lights.
Continue in a similar fashion moving to any of the items on that fuse. I do not have a wiring diagram post 1984 vehicles, but my wiring diagram covers the following items on No: 2 fuse, rear fog lamp switch, front fog lamp switch, o/s parking lamp and rear number plate lights. You have mentioned door light switches, include these in your testing.
I hope this helps.
the wiring for the rear fog lamp travels through a spiral duct attached to a spring retraction mechanism behind the interior corner panel ( along with wires for the rear wiper. heated rear window and central locking ) at the interface between the door and the door frame on the hinge side.... these wires are prone to chafing if the tube cracks or breaks as thisstops the retraction system from orking ( on early G's the wires are on the outside of the door / door frame and run through two rubbergrommets in the body and door and are apparently wrapped with electrical tape ...again they can bend and break or chafe and cause a short as a result
In reply to thread No: 3; you have the right thoughts in the tracking of your fault.
Regards,
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Thanks. I won't be able to try til next weekend, but will start with the number plate lights.
The thing is - if there is a short between the fuse/switch and the bulb, then removing the bulb doesn't prevent the short.
I will hope its a connection 'at the bulb fitting' that is the issue.
After that, the tow electrics. Since it blows when the side lights are switched on, its got to be related to the lights. I wil try 'quickly' turning the ligts straight to full beam (front side lights go off and its a different fuse for the main beam) and then I can test the door buzzer, interior dash lighting and rear fog light. It might also rule out the number plate lights being the issue. If it still blows, then maybe the rear side light is the culprit, or the number plate, or the tow elecs.
At the last MOT, garage apparently had to run a new feed for the rear fog light, and I am getting suspicious now where it was connected to. Might undo that work along the way.
Will let you know.