1500 electrical cutting out

[Chief1500]

My Spit had been running great, but then all juice to the interior of the car just cut out. The battery was charged, the headlights and horn worked, but I had no power to the ignition or any of the gages.

It cut out as I passed a semi going in the opposite direction, which tends to shake the Spit a bit, so I thought it might be a loose connection. After getting a tow home by the misses (you know that was tough) I decided to let the car and myself cool off for the night before diving in with the electric meter. The next morning it kicked right off. Now I'm nervous about taking it anywhere until I determine the cause.

Any suggestions? I can find nothing about any type of sensor that would cause a temporary loss of power.

 

[eejay56]

When mine started doing the same thing it was the ignition switch. You could wiggle the key and it would work.

 

[TR3driver]

Go to Radio Shack and buy a package of "test leads", the ones with the medium-size alligator clips. That way, if it happens again, you can hot-wire it yourself and not ask the missus for a tow.
https://tinyurl.com/29pmc4

 

[guzzul]

.. the headlights and horn worked, but I had no power to the ignition or any of the gages.

The ignition switch is a good place to start. It would be a common failure point for the ignition and gauges. And if it is going, then vibration could easily trigger a failure.

I would also check the top fuse carefully. You've got power to lights and horns, which are off the two other fuses, but the top fuse supports both the gauges and the ignition circuits. Check the fuse itself, tap it to see if the element is loose, and check the end-caps, and also check the mounting clips.

If you have the ignition switch turned on for testing without starting the car, remember to unplug the (-) terminal of the coil, and/or unplug the 3-connector plug to the dizzy, to avoid buring out your distributor amp.

 

[TR3driver]

but the top fuse supports both the gauges and the ignition circuits.

On most Triumphs, there is no fuse for power to the coil. And the diagrams I have for late Spits show the same thing. The fuse does protect most things controlled by the ignition switch, but not the coil.

Otherwise, I'd call the fuseholder a prime suspect.

 

[guzzul]

Yep, you're right Randall. It just occurred to me that the fuse is easy to check, and it seems like a candidate anyway. My prime suspect would be the switch.

When I mentioned the coil, what I was thinking was not to leave power on the distributor for any length of time while checking things out. Probably better to simply unplug the dizzy connection.

 

[Chief1500]

All fuses look fine. It acted up again yesterday - ran for a few minutes and then cut out. I did notice that there was some arcing in the voltage regulator (on the back of the alternator) when it was running. Could a bad voltage regulator be causing this? Looks like I've got the tedius task ahead to trace and test every line, connection and component between the battery and the coil.

 

[guzzul]

I doubt it. You should be able to run off the battery. Also you mentioned your horns were working and the battery charging, so I would not suspect alternator.

Did you check the brown-wire connections at the start solenoid? Have you checked the ignition switch?

 

[Chief1500]

The switch seems to be functioning correctly. It doesn't look like power is getting to the switch when the problem exists. I'm not familiar with the "brown-wire connections at the start soleniod". Can you expound?

 

[TR3driver]

This diagram might help. However, since the headlights and horns still work, I would not suspect the brown wire. More likely, IMO, the white/yellow or pink/white wires at the starter relay.
The pink/white wire is particularly suspect, since it is a special resistance wire that forms the ballast resistor. Because of that, it's more apt to break inside the insulation.

 

[Mickey Richaud]

NICE diagram, Randall! Even I can read that one!

Is there a similar one for the TR8 and MGB?

Mickey

 

[guzzul]

Yes, I thought that too, Randall, and well worth a look. But according to the first post, when the ignition quits, then the gauges quit at the same time, so there must be someting going on (or going off) in addition to the ballast wire.

I was looking for something (like the brown wire) that actually feeds the ignition switch. I was thinking maybe the smaller brown wire connection at the solenoid - or possibly a break somewhere in the small-brown wiring between the solenoid and ignition switch. The lights are getting power, and so are the horns, so I agree it can't be in that part of the brown-wire circuit.

 

[TR3driver]

NICE diagram, Randall!

Thanks ! Unfortunately I can't claim credit for it, or even offer credit where it is due. I snagged it off the 'net some time ago, before I started trying to save credits (but after I figured out that a lot of good information is later taken down; and started copying everything I thought was useful).

Is there a similar one for the TR8 and MGB?

Sorry, not that I know of.

 

[TR3driver]

But according to the first post, when the ignition quits, then the gauges quit at the same time, so there must be someting going on (or going off) in addition to the ballast wire.

Good point, I had forgotten that. If it's a "brown wire" problem, then it has to be somewhere between the 5-way junction and the switch. The switch itself still seems more likely, but if Chief1500 is certain it's not getting power, then it's got to be that length of wire.

I don't know the physical layout of a 78 Spit very well, but I would be looking in the vicinity of the switch for damage (or a DPO-ism) to the brown wire. If worst comes to worst (and you can get the problem to persist while you trouble-shoot), you can test for power on the brown wire, first at the starter, then at the switch, and then at points in-between. A needle-pointed meter probe (Radio Shack) can be used to pierce the insulation; or in a pinch, use an ordinary pin in vice-grips.

 

[guzzul]

NICE diagram, Randall! Even I can read that one!

These are Tom O'Malley's Spitfire wiring diagrams, and yes, they are terrific. They are still available at the Spitfire and GT6 Magazine web site. Link is https://www.triumphspitfire.com/wiring.html

As Randall rightly notes, better download it now, because you can't be sure this stuff will be there when you go looking for it. I packrat as much of this information as possible, regardless of immediate need....I know I'll reach for it one day.

Is there a similar one for the TR8 and MGB? Mickey

Not that I know of, at least not by O'Malley.The best electrical reference for MGB I know of is the Hammer and Spanner UK site.
https://www.mgb-stuff.org.uk/hammerframe.htm

If you go to the 'Electrics' page, there is some great discussion on diagnosis, and also schematics by subsystem. There is also a link to Dan Masters' MGB schematics, which are pretty good from what I can see.

I haven't seen anything for TR8 in my travels as yet.

 

[guzzul]

That's a good approach. On the Spitfire, the brown wires pass through the firewall on the LH side, close to the fuse box, as they head for the ignition switch. There is usually a 'bundle' there, where a number of those brown wires are commoned together, usually crimped together and wrapped. This would be a place to look also, both to see if there's some shorting against the firewall itself or if one of these wires has come loose from it's mates.

 

[Chief1500]

This is all great advice. It seems that a good way to test this would be to run a temporary wire from the 5 way junction or the battery directly to the switch.

Is there any function of that junction other than splitting up the juice? Are there any internal connections that could be causing a short to one of the output terminals?

It looks like I've got a full weekend. Thanks for all the help. I'll update you on Monday.

 

[TR3driver]

Just to be clear, you're looking for a "long", not a short.

No fuse, and connected to a battery capable of supplying 1000 amps or more tends to make brown wire shorts a memorable experience !

 

[guzzul]

Is there any function of that junction other than splitting up the juice? Are there any internal connections that could be causing a short to one of the output terminals?

As far as I can see, there is no other function of that bundle except as a common brown-wire connection point. It should be pretty easy to see sticking out of the harness.

I'm not sure what you mean about internal connections. You should be able to disconnect the battery and use an ohmeter to test continuity between that brown-wire junction and all the various ignition, alternator, fuse, etc ends that connect to those brown wires.

But I would think you are looking mainly at the brown wire that connects to the ignition switch. Hopefully you would not have to tear that bundle apart to test this. You will either have continuity to the junction or not. Note that there are two brown connections at the switch. I have not personally torn this part of the harness apart, but I'm guessing from the wiring diagram that there must be an additional connection between the junction and the switch (or at the switch itself) that adds the second connection.

Just to be clear, you're looking for a "long", not a short.

Yikes, absolutely. I should have said 'open circuit', not 'short. Indeed, if you had a short in one of these wires, you could just follow the smoke to find it, providing you look fast.