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Just became the proud owner of a 74 TR 6.  It came with no radio, so I bought a walmart special, installed it and it cuts out when the motor is running.  Runs fine when motor not on.  The company tells me that the radio cuts out at 14.5 volts, however, the out put from the alternator goes up to 13.3 or so .  I have checked all the wiring and it is hooked up properly.  Any ideas will be welcomed.

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Welcome to the forum. 

When you say it 'cuts out 'do you mean just the audio stops or does the whole thing go dead - lights out and all?  Despite what Walmart say that would be rather unusual behaviour.  Audio blanking might possibly be due to interference from the ignition.  What leads/plugs are fitted? 

As an aside, if your alternator does only go to 13.3 V when the engine is above 3000rpm there is something wrong.  Maybe your voltmeter is under-reading?

Edited by RobH
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 If the radio is going off as you crank the engine it might be because the voltage drops too far for a moment.  Even the simplest FM radio is likely to have something digital inside it these days, and digital can get very upset if the voltage drops too low. 

Hooking it direct to the battery might help as you say. Since it comes back on if you power cycle it with the engine running, it cannot be an interference thing.

 

 

 

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Hi Aridon

Check the wiring to the radio and around the ignition circuit area. The radio feed wire comes off the ignition switch. See this link to TR6 wiring diagrams and look at the 1974 version.

http://www.advanceautowire.com/tr2506.pdf

According to that there is a white/pink wire off connection 5 of the switch. You normally then have an in-line fuse between the radio and ignition.

Sounds like a power surge when you start the engine or maybe more likely a dodgy earth connection somewhere. If there is a dodgy earth wire to the engine or battery or alternator for example then it will try to earth through something else - in this case the radio. I remember on my 4A having a poor earth connection to the horns and the high beam warning light came on when I pressed the horn. Took a while to find that one. Once the engine is running then as you say you switch the radio off and on and it then works. I have just added an extra earth wire between the engine and body. 

If the radio works with the engine off then doesn't sound like the radio. I would start by cleaning up and checking all the earth points especially the wire between the engine and body. Not sure where that is on a 6 but on a 4A it is front left of engine to chassis.

Most of the electrical faults I have encountered are usually due to poor earth connections somewhere.

Keith

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a radio must work down to 11.5v else it is useless with the engine off and battery is semi state of charge.
You do need over 13.5 to charge a flat battery but my experience of cheap digital voltmeters is mostly all bad, +/- quarter of a volt is not uncommon on 20v ranges. A rough check for it on a good fully charged battery, engine and toys all off, should be about 12.6 volts.
Earthing is super important, measure radio volts at the radio, one meter lead stuffed in the fuse holder (radio side) and the other lead directly on the radio casing.
An earthing-check I use:
disconnect the coil to stop the engine starting.
use a GOOD voltmeter with one lead on the actual lead "earth" terminal of the battery (ie not the clamp) and the other on an engine head stud. Crank the engine on the starter and the meter should read leass than 0.3 volts, preferably less than 0.2 volts. this simple test will identify any poor joints on the primary earthing. Radios often benefit from a dedicated earth strap from their case to the bulkhead but keep the earth strap short as poss.
good luck,
MJ

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In modern cars the radio feed comes off an auxiliary contact of the ignition switch. This contact actualy gets disconnected when cranking the engine, probably to prevent the electronics in the radio from being affected by any elcrical disturbance caused by the starter motor. If your radio remains connected when cranking that may be the problem

Bob

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