23 replies to this topic

[H.M.M.]

Just got a Q about the voltages.

I'm getting a good 12v from the solenoid to the barrel via the Brown wire.
Turn the key to position 1 still good, go to position 2 (ign) and the voltage is not there.
Just to confirm that this is not right before I spend a fortune on a new ign barrel.
There is not any other feeds to the barrel I'm missing? I know the red/white wire is the power switch for the solenoid to starter.
I can't understand what would cause the main feed to the barrel go when you switch to ign????
Could a faulty solenoid do this?

[H.M.M.]

Just done the same voltage test from the alternator.
I get a constant 12v until I turn to ign then everything goes.
Solenoid???

[Yoda]

From where are taking the measurement. Out from the switch or at the solenoid?

[tiger99]

I suggest that it is a high resistance connection somewhere in the brown feed, the battery wiring or even the battery terminals or earth. The negligible current drawn by the multimeter will allow youi to see 12V, but when you turn the key to the nexy position, which draws significant current, the voltage will collapse.

Obviously there are a few places to check, like both ends of the brown main feed (check under the insulating boots, they sometimes corrode inside the terminals), but based on personal experience I would suspect battery terminals first (ok, do a quick check with headlights first, if ok, the battery terminals and earth are ok), followed by the brown feed wire.

[H.M.M.]

I'm taking the voltages from the wires going into the barrel and into the alternator.

[H.M.M.]

All the permanent power (lights, horn) are ok.

[H.M.M.]

Oops double post

Edited by H.M.M., 08 September 2012 - 03:15 PM.

[Ethel]

How are you measuring? The brown is the only supply to the ign switch. Later models may run some ignition stuff via a relay, but the ignition out from the barrel would be live.

[Ethel]

You won't see voltage if one probe's on the ign switch & the other is on the alternator as both will be 12volts, 12-12= 0

What is the fault you're trying to track down?

[H.M.M.]

Sorry forgot to mention this is a 1976 model. I've been looking on the wiring diagram. The only thing that I can think of is an after market immobiliser?? As this would cut all the power??
Gonna trace the wiring now.

[H.M.M.]

You won't see voltage if one probe's on the ign switch & the other is on the alternator as both will be 12volts, 12-12= 0

What is the fault you're trying to track down?

When the key is in position 1 I get 12v, when I turn to ign the voltage stops. So I cant start her.
I have checked voltages from the power into barrel and this is ok until the ign is on.
The same results from the alternator
But I am still getting 12v from the solenoid. So between the brown wires from the solenoid to the barrel and alternator I'm looking the reason the power is lost.

[tiger99]

As I said, a high resistance, and you now know that it lies between the solenoid and the ignition switch. Actually, it sounds very much like it is right at the solenoid terminal, if the voltage collapses at both the ignition switch and at the alternator.

I think you should have the stack of wires off the terminal, and check the ends of the brown ones carefully.

But where are you earthing the multimeter? It is just possible that if you are earthing it toi the engine, the engine earth is adrift, but if you are earthing to metalwork elsewhere we can rule that out.

[H.M.M.]

I'm earthing to the body. just checked the wires from the solenoid and they aren't the original.
they run to an aftermarket fuse holder then into the bulk head. looks like the go into a relay. seems to have an imobilser that I wasn't aware of.
I'm going to bypass the alarm by re wiring from the solenoid to the ignition barrel and alternator. What ampage wire would I need. I have 27 amp but not too sure if this will be strong enough.

[tiger99]

Well, that may well explain the problem. The immobiliser must leak some current, but not a lot. Best to put it back to standard configuration, and take it from there.

27 amp wire may not be really up to it, you may need more, to suit the rating of the alternator, it it is particularly high. If you rely on double wires from the alternator, please ensure that they are both the same length, and the terminals are very tight, so they do try to share the current something like equally. 27 amps will be enough to feed the ignition switch, unless you have some very weird electrical equipment in the car.

I don't know why the alternator has to be included in the immobiliser circuit anyway. It is very damaging to disconnect the alternator with the engine running, so no fuse, relay or anything else should ever be there. Obviously, like most Minis now, yours has a bit of history, not all in the hands of experts.

While you are at it, please check that the other brown feed, to the light switch, does not have a fuse or any other improper addition. You don't want to suddenly lose all lights, particularly headlights, on a dark night!

[H.M.M.]

Checked all the permanent feeds and they seem unaffected. Just seems to be the 3 main ignition feeds 2 to alternator and 1 to ignition. But by changing the main ignition feed first and take it from there.
The wiring behind the dash is a real mess.