Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Blowing Fuse No. 10

Could I ask the electrical wizards out there to shed some light on my latest problem.
Fuse 10, TSM, 5 amp keeps blowing, sometimes it can take 30 seconds or so sometimes as soon as the indicator stalk is used. When it blows I loose all dash lights, displays, rev counter, speedo and starter button.
It does not appear to affect the hazard warning lights, but if I turn the hazard warning light switch on after the fuse has blown all the above work as long as the hazards are flashing.
Is it the dreaded TSM that is on its way out I wonder.

Fuse 10 supplies TSM and switch connector (on pre 2014 models) and is itself fed by ignition switch. Hazard lights are fed by permanently live fuse 2 so not too surprised at your findings as some back feeding taking place.

Note the TSM appears to be different on later post mid 2014 models as the connector is an 18 pin one (16 used) whereas earlier type which I believe you have, uses a 12 pins. Note also earlier models had isolation diodes added externally to left and right indicator circuits at switch connector probably to avoid hazard wiring causing cross feed. Might be worth checking these although probably covered with heat shrink.

TSM's seem to have random built in issues from new even the later ones but I would be tempted to increase fuse 10 size from 5 to 7.5 or even 10 amps and see if that cures blowing issue.

Thanks Richard, it's a Feb.2013 but built in Dec 2012 so like you say will be the 12 pin variety. I did think about upping the fuse size to 7.5 amp but then thought it must be 5 amp for a reason so left it at that as I didn't want to cause any more problems.

The 2 diodes that you mention would they be inside the steering column shroud or buried in the back of the dashboard.

Firstly the diodes are a long shot but being IMHO something of an afterthought bodge (since they are not used on 2014 on models) come under suspicion. The wiring schematic shows them on the chassis loom connector to the dash switches so wherever that is you should find them, likely covered in heat shrink. They will be fitted to the standard green/white and green/red indicator wires.

You may know that I had a 2016 car for two plus years covering 9000 miles but now have to rely on documented info. My car did have a very occasional glitch where from now distant memory the sidelights came on uncommanded and wouldn't respond to light switch but I found operating the hazard switch cleared the situation. Others report similar bizarre behaviour, almost certainly attributable to the TSM, this makes me wonder if the logic within has a bug whereby the relays latch themselves into a random knot. Pure speculation on my part but the only explanation I can offer when the unit otherwise continues to work fine.

It's your call on the fuse size with the policy being they should use values to adequately cover the highest circuit load. I have actually reduced related fuse sizes on my Roadster after going to full LED's. I cannot see that increasing to 7.5 amps would do any harm though. I recall increasing fuse size twice on the hazard/horn fuse 2 when it kept blowing, finally traced to a supplied faulty relay coil to air horns!

BTW what happened to the guy who had reverse engineered the TSM (which version though!) and was going to offer a plug-in replacement?

The reverse engineered and improved 16 pin TSM was produced by Alister and still is I believe. I have his email contact if anyone needs one still. Unfortunately not the 12 pin early type. There is an article about this in the MTWC Bulletin Jan 2022.

Good to know Ian but unfortunately no help to the many earlier model owners who, correct me if I'm wrong, have seemingly greater TSM issues.

I know some 12 pin modules have failed but the majority seem to be the later 16 pin ones but that may be because there are more of them about? Alisters version is "hardened" to reduce the chances of failure with voltage spikes, along with some extra features like a variable cancel period. Not a help to early TSM cars ....unless someone can come up with an adaptor to make a 16 pin TSM work with a 12 pin loom? A handy thing to know is that although a faulty TSM can produce some weird results such as not allow the engine to stop, random hazard lights etc. the car will run without it fitted, just no indicators. Get you home with some hand signals.

Thanks for all your electrical diagnosis Richard. I still struggle to read those circuit diagrams, not the easiest!

I would be interested to know exactly where the two diodes are supposed to be fitted on the earlier cars Dab, if you can find them.

@ Lee the diodes are just outside the loom near the fuse box. You can see them, but you need to learn how to test them as it's such a short piece of wire where they are on.
I will try to make a picture so it's easier to find them.
For the pre-2014 models, the upgraded TSM don't fit. I will send Alister an email today requesting if it's possible to produce a 12-pin TSM for the ones with older cars.
Can you get a hand on a TSM from another car to see if the problem is in the TSM or in the wiring?
As you can read in my idling post, when I put a good working TSM from the other car, it blows several fuses when turning on the lights.
I made a print from the wiring diagram on an A3 size so it's clearer to study how the connections are laid out.

@Richard Do you have a scheme from the colour abbreviations used in the wiring diagram?

I can’t remember what the TSM is?

So far as I know, are these the diodes at the instrument panel connection.
How to check if working correctly without taking the wiring apart?








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