Can I Bypass Electrical Short

[j.collins]

hi guys i have another post describing my problems with brake light failure.

however can i bypass a short.

 

i want to run 2 wires from top of brake switch directly to brake lights at rear of car.

is this possible?

as i cannot isolate the short.

there is power in the 2 wires coming from the top of brake switch.

thanks for any replies

[Scorpiorefugee]

Can I suggest that you stick to one topic at a time as this gets confusing and counter productive. Just put a link to your first topic and let this one die.

 

I doubt very much that it is as simple as a direct link between pedal and lights as there are, among other things, current measuring devices in the system.

 

You have already made a list of other symptoms that seem to be linked and it may be more productive to go trough the tests again trying all possible combinations and then chase the one symptom which seems most stable and therefore easier to trace. The dim headlamp may be a good place to start. A dim lamp is going to be a low voltage across the bulb due to high resistance or loss of a common ground connection and this can be either on the feed or return. Use a voltmeter to check voltage on both sides of the bulb - remember to use the battery -ve as the -ve on your meter. It may also be worth checking the voltages on the tail lamps at the same time. The problem with complex systems is that you need to look at the whole picture and understand it so it may be worth investing a bit of time there before you start bridging wires.

 

I wish you good luck, you will probably need it.

[Mirez]

As above really it would be a bad idea to directly link - on modern cars its far more likely to be a logic signal at the brake switch and not the actual feed so taking a wire to the brakelights from there could, potentially, cause significant damage to the controller.

 

If the brake lights come on when you put the lights on then thats an obvious short, and one that could happily cause a dimming with the additional current required. I didn't think P reg cars had the third brake light? Is that aftermarket? Start there if it is!

 

If not then you'll need to start measuring voltages and resistances as Scorpiorefugee suggests, check the brake pedal switch first. It will probably be taken to ground when the switch is depressed so check in the resistance of both wires with and without the switch activated. (if its a high circuit it'll need 12V on one side when not depressed and 12V on both wires when activated)

 

Next I would remove the brake bulbs and fuse and measure reistance on both sides. One should be low and one should be high, if both are low then the short is on that wire. Disconnect the wiring at the tailgate entry and find the wire in that connector. Measure again. If it remains low the problem is in the tailgate wiring if its now high then its probably in the vehicle - with the tailgate loom disconnected measure continuity across all the other wires - any that show could be possible shorts in the tailgate loom so identify what they control and repeat. Once you've exhausted the tailgate loom you can move on to disconnecting clusters and headlights but I'd be suspicious of the tailgate wiring as it enters as so many seem to fail at that point.

[Scorpiorefugee]

See! We're already confused. I don't know which topic to chase. :D

 

:D :D :D

 

When you turn on your headlights, do the stop lights come on full or dim. My guess is dim suggesting a shared ground connection problem. It might be worth starting to chase the wiring from there and if you want to try bridging any wiring, try a new chassis connection for the stop lights.

 

Just make sure you get the right one.

Edited October 17, 2009 by Scorpiorefugee

[sparky Paul]

Duplicate threads do make it hard going, and I haven't seen the other one.

 

I assume that the OP has checked the common wiring failure point at the tailgate? :D

[j.collins]

sorry guys about duplicate thread.

you gave me some good advice.

i now have a better idea.

thanks