Instrument lights, etc.

[Member 10617]

After having my engine and transmission rebuilt and the car put back together, I find that the instrument lights don't work, the fan for the heater doesn't work, and only the low horn sounds. Since these are all located close together, can there be a single cause? I've looked for a separate fuse under the dash, but can't find anything.

 

[Andrew Mace]

Not sure about the horns, but it could be a lack of ground causing the rest of the items to not work?

 

[Member 10617]

I'm not sure where this ground would be. I have cleaned up the main ground from the battery and the ground from the voltage regulator. Don't know where to look for grounds for the lights and heater fan.

 

[mrv8q]

Disconnect the battery, and clean up the fuse box itself. If you have one, the fuse holder is behind the gauge panel, directly underneath the push-to-start button.

 

[Member 10617]

I cleaned the main fuse box a couple of days ago and checked the fuses. There is a 35A fuse in the LH fuse holder (as called for in the Triumph manual) and a 50A fuse in the RH fuse holder (needed because I had an electric fan installed). There is no fuse holder behind the gauge panel, underneath the push-to-start button.

 

[TR3driver]

Your car may be too old to have the in-line fuse behind the panel.

I think I already mentioned this, but JIC : the fuse ratings given in the Triumph documentation are using an obsolete Lucas rating method, that results in the numbers being about twice what a modern fuse of the same capacity would be. Thus if you are going to use modern fuses, they should be rated 20 and 25 amps respectively.

There was an interesting demonstration at VTR/SP a few years back, where they first loaded a proper Lucas fuse until it blew, and then inserted an AGC fuse with the same rating, plus added some more load. Not only did the fuse not blow, but a minute or so later the smoke started leaking out! There have been cases reported of the same thing happening with people's cars ...

From your description, I strongly doubt that all 3 symptoms have the same cause. For the panel lights, are you sure the switch is turned on ? (Both the headlight switch and the 'panel' switch must be on for the panel lights to come on.) Do the lights in the tach and speedo work? If all 6 bulbs (2 each tach/speedo, 2 more for other 4 gauges) are no-shows, but the taillights work, I would guess it's the 'panel's switch or the wiring to it.

For the 'high' horn, it might be the wiring to the horn (I fought an intermittant horn problem for a long time that turned out to be a connector sleeve that had broken internally and wasn't making good connection). The horn don't depend on a ground to the body, they get grounded through the horn button when it's pressed.

But more likely it's the horn itself. There is a pushrod inside that operates the contacts, and it tends to get corroded and stuck. The contacts could probably also use cleaning and adjustment.

Heater fan could be either the control (they are notoriously troublesome) or the fan motor itself. There is a separate ground wire, so not likely to be a ground problem unless someone has left the wire disconnected. Or perhaps the power wire is disconnected or broken. This is one of those cases where it would make a lot more sense to poke around with a test light, before starting to replace things. Ground one side of the light and turn the key on before you climb under the panel, then touch the probe to each terminal in turn of the heater control. No lights means the wire from the ignition switch is bad; one light means the control is bad; two lights means the problem is the motor (or wires from it to control & ground).

 

[TR3driver]

Oh yeah, forgot to mention : If your car does have the in-line fuse behind the panel, and it is blown; then the tail lights will not work either.

 

[Member 10617]

Randall,

All your good information has given me the ammunition I need to attack this mystery. I will get started right away! Having information is always the first step, and thanks to you I am now armed against the Lucas gremlins.

As for the fuses, I put a Lucas 35A fuse in the RH fuse box and my new electric fan stopped working (no fuse blown). I replaced the Lucas 35A with a new 50A from Moss and the electric fan began working again. It doesn't make sense to me, but it works.

Should I replace the Moss 35A presently in the LH fuse box with a 20A fuse? Should I replace the Moss 50A in the RH fuse box with a 25A fuse? If I do change the RH fuse, won't the electric fan stop working again as it did with the Lucas 35A fuse?

Yep. I think my car is older than some of the improvements made to the later TR3As. Hard to think that I was 21 when I had a "new" '58 back in '62.

You should write a book!

 

[Member 10617]

Panel light solved. Stupid me! I did not know, or had forgotten, that the head lights had to be on for the panel lights to work.

That "problem" solved. Thanks Randall.

The fan motor still does not work, but -- after all -- I don't need it now that the temp around here is 90-100 every day. Manana, manana... as they say.