TR6 oil light problem

[deano]

I have got a problem with the oil light on my 1973 TR6. With the ignition off the light remains on(!) however once the car is started the light goes out. Can anyone point me in the right direction to what might be wrong?

 

Thanks (new member)

[TIMS]

Deano

 

What is happening to the ignition light? if that never comes on at all, or only on startup from cold, it is quite possible that the bulb holders have gor swapped over beheind the rev counter and your oil light is infact the ignition light and vice versa.

 

Regards

 

Tim

[Kevin Warrington]

Have you made any changes or additions to the wiring, or have you only recently bought the car? I've got my "Owner's Guide" book in front of me - it is a reprint by Brooklands Books and the wiring diagram is hopelessly incorrect in that the numbers shown in the key do not match up to the numbers in the wiring diagram.

 

Looking at the factory workshop manual, I can see that the light is fed directly from the ignition switch and earthed through the pressure switch. So you'll have a wire from the switch to one side of the bulb carrier and from the other side of the bulb carrier to the oil pressure switch. When the pressure is low, the swich closes, earths the circuit and the bulb lights. As pressure rises, the switch opens and the light goes out.

 

With the ignition on, but the engine not running, locate the oil pressure switch (I think it is down the front at the bottom of the block on the nearside). Pull the wire off and the light should go out. Or, perhaps, more exactly in your case, a light *somewhere* might go off. Put the wire back on the switch and the light (or a light) should come back on. It might be as Tim has just written that bulb holders have got crossed somewhere, although that would not explain why the ign light was on when the ignition was off.

 

Kevin

[deano]

Have you made any changes or additions to the wiring, or have you only recently bought the car? I've got my "Owner's Guide" book in front of me - it is a reprint by Brooklands Books and the wiring diagram is hopelessly incorrect in that the numbers shown in the key do not match up to the numbers in the wiring diagram.

 

Looking at the factory workshop manual, I can see that the light is fed directly from the ignition switch and earthed through the pressure switch. So you'll have a wire from the switch to one side of the bulb carrier and from the other side of the bulb carrier to the oil pressure switch. When the pressure is low, the swich closes, earths the circuit and the bulb lights. As pressure rises, the switch opens and the light goes out.

 

With the ignition on, but the engine not running, locate the oil pressure switch (I think it is down the front at the bottom of the block on the nearside). Pull the wire off and the light should go out. Or, perhaps, more exactly in your case, a light *somewhere* might go off. Put the wire back on the switch and the light (or a light) should come back on. It might be as Tim has just written that bulb holders have got crossed somewhere, although that would not explain why the ign light was on when the ignition was off.

 

Kevin

 

 

I have made no changes or additions to the wiring since I brought the car 18 months ago and its been running fine. When I got home last night I reconnected the battery (didn't want the flatten it by leaving the oil light on) started the car up (battery was fine) and drove the car out of garage. However when I tried to restart the car about 10 minutes latter the battery was flat! All very odd but the oil light problem must have a 'connection' with the battery going flat

[Kevin Warrington]

yes - very strange. Assumming that the battery is OK, as a rule of thumb the battery would need about 75% of its nominal full charge to start the engine. Typical capacity is around 80 amp-hours, so you would need to "loose" something like 20 amp-hours before you had starting problems, which in 10 minutes would imply something like a current draw of 120 amps. For the purists, I know that there are some appalling generalisations here. So while it might be "connected", it might be a red-herring as 120 amps is more-or-less welding things and well in excess of what the wiring or the fuses would stand and you would probably be seeing smoke. So perhaps you have another problem in that the alternator is not charging. This might be something - the excitement voltage for the alternator is fed via the so-called ignition light and I think I would be very inclined to check the wiring to make sure nothing has fallen off

 

Kevin

[deano]

yes - very strange. Assumming that the battery is OK, as a rule of thumb the battery would need about 75% of its nominal full charge to start the engine. Typical capacity is around 80 amp-hours, so you would need to "loose" something like 20 amp-hours before you had starting problems, which in 10 minutes would imply something like a current draw of 120 amps. For the purists, I know that there are some appalling generalisations here. So while it might be "connected", it might be a red-herring as 120 amps is more-or-less welding things and well in excess of what the wiring or the fuses would stand and you would probably be seeing smoke. So perhaps you have another problem in that the alternator is not charging. This might be something - the excitement voltage for the alternator is fed via the so-called ignition light and I think I would be very inclined to check the wiring to make sure nothing has fallen off

 

Kevin

The problem has been resolved. The oil and ignition lights were swapped around(!) and the alternator had a short in it that would explain the rapid discharge of the battery (the alterator was quite warm!)

[Kevin Warrington]

Thanks for letting us all know the outcome. it seems amazing that you can get 2 faults at the same time, but it happens to me all the time

 

K