series 3 headlamp fuse easily blown

[ernest.irw]

Help! My series 3 headlamp fuse is easily blown, I've replaced it constantly. I've tried 25A, 35A fuse. The fuse is second from bottom, under the steering wheel cover. If it is blown my headlight, brake light is gone, fuel indicator and wiper is also gone but the turning signal works just fine. Has anyone experienced this before or can refer me to links that discuss how to diagnose this issue and fix it? Thanks!

[Opabob]

I'm sure others will have better suggestions, but I would try moving the various circuits one-by-one off the fuse that's blowing. Then wait and see what happens.

I have started building a newer fuse block to deal with aftermarket things like an air compressor, electric fuel pump, etc. I move over standard things like turn signals, etc. to new fuses as I work on electrical problems. I reserve one switched and one unswitched fuse to help diagnose issues like this.

[ernest.irw]

Thanks Opabob, it is a long holiday project then. I am currently using hella h4 light fitted with relays, I suspect the culprit is the main headlamp cable. Rebuilding newer fuse box is a good idea though. Thanks.

[SafeAirOne]

Behind the plastic grille is where the lighting wires cross over from the right side to the left. This wire bundle is held to the top of the radiator support panel by sharp metal clips. After years of vibration, these sharp metal clips chafe through the wiring, creating a path to ground (a short).

You might check the wiring in the area of these clips.

[slowmo]

Does it immediately blow or does it take a little time? If it immediately blows you have a dead short to ground somewhere. Might be headlights, could be running lights. You should then disconnect the connectors where SafeAirOne said one at a time. Use a multimeter in continuity mode (the mode that beeps when the probes are touched together). Connect one of the probes to ground. Touch the other one to the wires running to the lights. When you find one that "beeps", there is your short.

[mearstrae]

If you're going to check anything on the ohms scale for continuity (some meters have a continuity setting, some only the ohms setting) be sure the battery is disconnected first, or you may get more than a beep from your multi-meter. As has been said check one circuit at a time, starting from the power source end of things. It may be bad wiring (a bare wire touching another - shorting- or going to ground) or a bad connection on either end of a wire (a switch or lamp housing shorting or grounding). And never discount a wire that's too small a gauge to carry the load, this can happen, even if a wire seems the proper size, it could have internal damage limiting how much current it can carry. This causes an overload as the resistance goes up, but can be harder to find with a continuity test. A corroded connection or a broken connection may also be found.

'99 Disco II
'95 R.R.C. Lwb (Gone...)
'76 Series III Hybrid 109
'70 Rover 3500S

[ernest.irw]

Thanks for the advise everybody, it is definitely a short. I've replaced the running lamp and found that the previous cable seems connected improperly, I grabbed the cable and it feels hot when I switch the running lamp on. I've finally sort it out using continuity and volt tester, now I only use a 25A fuse and it is fine. Thanks! this is a great forum.