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Batteries discharge in 2/ 3 days, can i fit isolator to kill all power including the seperate red wire which presumably is for radio/tacho?

I am not sure what seperate red wire does and would like to isolate everything as i leave truch for weeks at a time

Posted by Anonymous on


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Fitting an isolator is a drastic step. You really need to discover the source of the problem.

Choosing a location for the isolator is also important and I would recommend talking to an auto-electrician first in case this is a well known fault with your make and model.

Posted on Mar 30, 2015

Testimonial: "thanks for that, have checked and it s not common apparently, was fitting isolator anyway, just can t figure out what this wire does?"

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Yes you can install a shutoff switch which is very common on bulldozers and other heavy equipment. the separate red wire on the positive cable goes to the alternator. that is the wire that charges the battery while you are driving. you have a drain on the battery which can be compressor clutch or security system or trunk lite or glove box light.

Posted on Mar 30, 2015

Testimonial: "thank you, will check out wiring to confirm charging line, cant find anything which is causing drain, not sure what you mean by compressor clutch"

  • 1 more comment 
  • Stuart Kirby Mar 30, 2015

    the air conditioning compressor clutch can remain activated when the switch is off and can drain battery rather quickly

  • Anonymous Mar 30, 2015

    thanks again stuart, have sussed it, looks like diode on alternator is causing drain, am sourcing replacement j

  • Anonymous Mar 30, 2015

    just to say thanks stuart again, i m not going to have internet for a while so your help was much appreciated, j



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How to use the battery disconnect switch correctly

The battery isolator switch, where one is fitted, can be to increase vehicle security or to help prevent vehicle battery discharge if it is left unused for long periods.

However it is wired the battery switch must never be used while the engine is running.
Isolating the battery when the alternator or generator is producing current can cause a voltage surge that is capable of destroying every bit of electronic equipment fitted to the vehicle.

Best practice is to isolate only after the engine is switched off and stopped turning. If an electric cooling fan is fitted the engine should be allowed to cool a little before isolating.

Feb 12, 2015 | Cars & Trucks

2 Answers

How do i fix the tachometer?

you have an in cluster factory engine tachometer (RPM)?
the tacho is meter in the cluster and does not use speedo parts or its cable.
its just a meter that needs power, ground and spark tacho signals
if all 3 are good, the meter is bad. period.
the tacho signal goes to the ignition coil minus lug, and will good, as engine runs. so... wires bad, to tacho or tacho bad.
ever price a new one? or even used? $100 used?
you willing to pay that much for just a factory tacho?

there is NO speedo cable. this old 93 is electronic, (rare on most 93 cars made, toy is advanced)
here is the proof, amazing how books dont lie....
there is a speed sensor.
the tacho and speedo use the same power and ground
leaving just one wire,r-g red-green RPM sig. pin 5 of cluster
an is SPARK primary sig. so if only tacho is dead.
then the tacho is bad, or that pin 5 wire is dead.
got you to just 2 possibles.


Jan 26, 2015 | 1993 Toyota Corolla

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Seat ibiza faults

Check alternator charge rate and earth straps

Jun 19, 2014 | 2007 Seat Ibiza 1.2

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Lights on the dash and radio dim in and out after starting But runs fine. Also the powered locks won't open with a remote it all happened at the same time. The car is a 2007 handa civic With 90,000 Km

old post day. zero resp. i fill vacuums.
answer low battery voltage. lots of ways, can be....
in no ORDER, only testing finds TRUTH.
1: bad battery ( or just discharged)
2: you cranked the battery flat. (discharged)
3: the Charging system is bad. (battery then becomes discharged)
4: corrosion in the the wiring and connectors in the above.

even a rusty fuse , on older cars. but too is #4

Sep 11, 2013 | 2007 Honda Pilot

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1993 BMW E36 325i odometer and clock won't turn off and kills my battery

fit a battery isolator inside the car under the dash on the battery earth is the cheapest soloution.Or a wiring diagram to trace the wires to locate the fault which i suspect could be on the radio wiring where 2 feeds are used one a permanant 12v feed and one a switchable feed via ignition switch causing a backfeed if done wrong .

Sep 22, 2012 | BMW X3 Series Cars & Trucks

1 Answer

Battery is discharged

If she turns off the radio and the battery stays up, it is easy enough to fix. But I do not think enough power is used to completely discharge the battery overnight.

Intermittent shorts are very hard to find, so you really can not blame the repair facility for not being lucky enough to find the problem. It is really a hit or miss situation to catch the defect when it occasionally happens.

There are a few cheaper parts to guess with as causes. A bad ignition switch may not turn off when the key is in the off position. Relays for the ignition, fuel pump, or electric cooling fan may not release when the ignition is switched off. Rear defrosters will silently drain the battery.

What you are looking for is something which does not blow a fuse, yet uses enough current to kill the battery. Bad diodes in the Alternator can easily drain a battery, have the Alternator tested for Diode function.

Can't say how much power the Alarm system is suppose to use. It is one of the few systems which operates with the car turned off. Again, whether it can draw that much power in a short period of time is questionable.

You can get free wiring diagrams at after registering your car. They also provide Relay box diagrams.

You can safely use an Ohmmeter on the circuits when the battery is disconnected. The idea is that the positive and negative wire leads are suppose to be separate. If you find a positive wire that is letting the Ohmmeter ground to the negative side, you have found the short. The 2 charges do not mix in things that are turned off. It means that the positive wire is touching the frame somewhere or powering a lightbulb or electric device instead of breaking a fuse.

I hope my solution helps you. Since you paid someone to fix this and some States require at least 30 days for repair Warranties, take it back.

Sep 03, 2012 | 2002 Toyota Tundra

2 Answers

Recharged battery. drove car all day no problem. Car sat for 4 days and will not start.

well the very 1st thing u do is have the battery tested, bet it has a dead cell. let me know.

Nov 12, 2009 | 1988 Toyota Supra

1 Answer


its the red and white wire behind the guages

Mar 19, 2009 | 1989 Nissan Pulsar

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