TR2/3/3A Electrical Issue

[SteveBones]

I have "new" electrical issue with my 1958 TR3A. When I turn the key, nothing happens. What I mean is that the red generator warning light is dark, the fuel gauge stays at empty, and the amp meter does not move. The horn does work. This happened after driving the car for 20 minutes with no issue. A few minutes after shutting off the car, and turning the ignition key to the on position, nothing happened. I just started trying to track down the problem. So far I have done the following:

1) Checked the battery connections. The ground wire was loose at the terminal. I tightened and no change.
2) Fuses. These are the original type fuses. I removed and cleaned the fuse connection ends. No change.
3) I plan to use a voltage meter with the resistance setting to determine is the ignition switch is working correctly.
4) I will take a look at the wiring diagram and start working from the ignition switch to see if there is a bad connection.

Based on what I describe, is there any recommendations on what else to do to isolate this electrical issue?

Thanks,

 

[CJD]

I would look closely at the ignition switch itself. The wires can easily loosen under the set screws.

 

[SteveBones]

Thanks for the suggestion on where to start. I looked under the dash and lightly pulled on the wires to see if they were snug. Based on your suggestion, I am thinking of going a step further by loosening the set screws, removing the wires, and the re attaching.

I would look closely at the ignition switch itself. The wires can easily loosen under the set screws.

 

[TR3driver]

Before starting to take things apart, I suggest some simple tests with a test light (or voltmeter/DMM/what have you). The switch is certainly a possibility, but there are lots of others.

Since the horns work, I'd start with terminal A on the control box to ground. It should be hot (12V) all the time. If not, there is a problem along the circuit from the starter solenoid to the ammeter, and ammeter to terminal A. Could also be a bad ammeter.

Also check terminal A1. If it's not hot, the control box has failed.

Then with the key on, probe both terminals on the back of the ignition switch. If you feel around a bit, you should be able to get on them without sticking your head down there. If neither one is hot, the problem lies along the circuit from A1 to the headlight switch, to the ignition switch.

If one is hot and not the other, the switch has failed.

If both are hot, check next at A3 on the fuse block (one white wire). Etc.

 

[SteveBones]

Extremely helpful Randall. I will do as you suggested below. I do have a voltmeter and have used it to isolate an electrical issue on my other Triumph about five years back. I will let you know what I find out.

Thank you

Before starting to take things apart, I suggest some simple tests with a test light (or voltmeter/DMM/what have you). The switch is certainly a possibility, but there are lots of others.

Since the horns work, I'd start with terminal A on the control box to ground. It should be hot (12V) all the time. If not, there is a problem along the circuit from the starter solenoid to the ammeter, and ammeter to terminal A. Could also be a bad ammeter.

Also check terminal A1. If it's not hot, the control box has failed.

Then with the key on, probe both terminals on the back of the ignition switch. If you feel around a bit, you should be able to get on them without sticking your head down there. If neither one is hot, the problem lies along the circuit from A1 to the headlight switch, to the ignition switch.

If one is hot and not the other, the switch has failed.

If both are hot, check next at A3 on the fuse block (one white wire). Etc.

 

[SteveBones]

Hi Randall,

A brief update and question.

1) Tested both A and A1 contact points on the control box. Both reading approximately a minus 12.5 volts so looks good (My set up is positive ground) . Next up is testing testing and working on the switch itself.

2) Regarding the A3 on the fuse block. Does this check to make sure it is hot - also 12volts? Does this A3 test only work if the switch is working and turned on? I do plan to check the switch out first.

Thanks for all the help from you and the others. The quality and willingness of the fellow British Car Forum members to share their expertise is so greatly appreciated.

Before starting to take things apart, I suggest some simple tests with a test light (or voltmeter/DMM/what have you). The switch is certainly a possibility, but there are lots of others.

Since the horns work, I'd start with terminal A on the control box to ground. It should be hot (12V) all the time. If not, there is a problem along the circuit from the starter solenoid to the ammeter, and ammeter to terminal A. Could also be a bad ammeter.

Also check terminal A1. If it's not hot, the control box has failed.

Then with the key on, probe both terminals on the back of the ignition switch. If you feel around a bit, you should be able to get on them without sticking your head down there. If neither one is hot, the problem lies along the circuit from A1 to the headlight switch, to the ignition switch.

If one is hot and not the other, the switch has failed.

If both are hot, check next at A3 on the fuse block (one white wire). Etc.

 

[TR3driver]

Yes, A3 is only hot with the key on, and should be close to battery voltage (12 volts).

 

[SteveBones]

One more question. When I am using the multimeter to measure voltage, since my TR3 is set up for positive ground, do I put the red (hot) wire on ground, and put the black (common) wire on the circuit (A, A1, A3)?

Brief update. I did check the switch itself. Even took it off to bench test by measuring resistance. I also cleaned the contact area. The switch is working fine.

Also, As mentioned previously, I measured the voltage for A, and A1 on the voltage regulator. Both A and A1 measured approx 12.5 volts.

Next step is to measure voltage at A3. I will try to do this sometime tomorrow.

Yes, A3 is only hot with the key on, and should be close to battery voltage (12 volts).

 

[TR3driver]

With respect to the meter, think of red as positive and black as negative. So, for a positive ground car, the red goes to ground and the black probes for power.

You might want to double-check the voltages at the switch, with the switch on and a load applied. A resistance like 1 ohm can be hard to measure; but is enough to keep it from powering the car. Also, sometimes things get hot and the resistance goes up when powering a load.

 

[SteveBones]

Here is my update:

1) A3 voltage was measured with the key on. Measurement was 0.00 volts. I also measure the other side of the fuse connection with the brown wires. I did measure approx 12.5 volts.

2) Switch voltage measurement was also 0.00 volts with the key in the on position.

3) One other item I noticed. Before this electrical issue, I was able to turn on the instrument lights, parking lights, and headlights on without the key. None of these items are currently working.

I am looking forward to hearing further suggestions. Based on the testing so far, it the issue with the switch, is further testing needed to isolate the problem?

With respect to the meter, think of red as positive and black as negative. So, for a positive ground car, the red goes to ground and the black probes for power.

You might want to double-check the voltages at the switch, with the switch on and a load applied. A resistance like 1 ohm can be hard to measure; but is enough to keep it from powering the car. Also, sometimes things get hot and the resistance goes up when powering a load.

 

[TR3driver]

Ok, so you found power at one end of the NU wire (A1 on the control box) but nothing at the other end (one of the ignition switch terminals). It daisy-chains through terminal A on the headlight switch, which is where I would look next (especially since now it appears the headlight switch isn't getting power either).

 

[DavidApp]

Hello Steve

Are you getting battery voltage at "A" on the control box? If you are you should have it at "A1" as well.
If you do not have voltage at "A" you probable have a bad Ammeter or bad connection.
If it is at "A" but not at "A1" a control box problem.

David

 

[sp53]

I am probably missing something, but isn’t the ignition just an on- off switch and you could hook a jumper across the back and see if the light comes on ---or would that hurt something?

 

[SteveBones]

Sounds good. Based on what you suggested earlier and the latest test results, I went through the wiring diagram to see if I could figure out what to do next. I was thinking the next step was to look at the headlight switch but was not sure. Thank you for confirming.

I have done quite a few things over 40 years fixing various items on my TR's. This is the first time having to resolve this type of electrical issue. I am starting to feel better knowing I am getting close. Without your help I am not sure how long and how much frustration I would have endured trying to fix this. Many thanks.

Ok, so you found power at one end of the NU wire (A1 on the control box) but nothing at the other end (one of the ignition switch terminals). It daisy-chains through terminal A on the headlight switch, which is where I would look next (especially since now it appears the headlight switch isn't getting power either).

 

[SteveBones]

Thanks David. Next step will be looking at the headlight switch wiring. I feel like I am getting close.

Hello Steve

Are you getting battery voltage at "A" on the control box? If you are you should have it at "A1" as well.
If you do not have voltage at "A" you probable have a bad Ammeter or bad connection.
If it is at "A" but not at "A1" a control box problem.

David

 

[SteveBones]

Makes sense what you are suggesting. Randall's method has been great in getting me closer to identifying the issue. What he is suggesting is based on starting at point A and moving back step and step through the wiring. This is the first time for me using this approach and also the first time having to address this type of electrical issue. As I go through what Randall is recommending, it is looking like a solid approach and helps to make sure I do not miss something.

I am probably missing something, but isn’t the ignition just an on- off switch and you could hook a jumper across the back and see if the light comes on ---or would that hurt something?

 

[TR3driver]

BTW, there is no reason you can't connect a jumper across the ignition switch. I have been known to drive that way, when necessary. Just be careful that it can't touch anything else, as there is no fuse in the feed to the switch and a short can easily set the car on fire.

But as noted, I much prefer a systematic approach, rather than guessing.

 

[CJD]

These switches are very robust...but they do use bakelite, which is very brittle. I would take a test light and follow the power in and out of each switch until you find the break.

 

[TR3driver]

When my TR3A ignition switch failed, the contacts were worn until they no longer made solid contact. The moving contact is spring loaded, but can only move so far.

 

[SteveBones]

Good point. I did test the switch, but after going through Randall's earlier email, I did not test the voltage correctly. This morning I will test the voltage of the switch by what was suggested earlier which is copied below:

Then with the key on, probe both terminals on the back of the ignition switch. If you feel around a bit, you should be able to get on them without sticking your head down there. If neither one is hot, the problem lies along the circuit from A1 to the headlight switch, to the ignition switch.

If one is hot and not the other, the switch has failed.

These switches are very robust...but they do use bakelite, which is very brittle. I would take a test light and follow the power in and out of each switch until you find the break.