TR4a Intermittent failure of instruments, indicators, wiper motor etc...

[DomJ]

I’ve recently experienced a problem where the fuel gauge and temperature gauges suddenly seemed to fail. I didn’t realise until afterwards but when this happened the indicators, wiper motor and heater blower all don’t work as well. The symptoms seem to vary greatly though ...sometimes everything works, sometimes nothing ... today when I looked at it the fuel gauge was working, until I flicked the indicator switch at which point the fuel guage dropped back to zero ... (no indicators or anything else either at that point) ... having then tried to tidy a few other niggles up with the wiring, it all worked again ... until I drove the car at which point it all started failing again .. my suspicions have centered around the stabiliser, or a loose connection, or a short. Can anyone help me with where to start with this ...? 

Edited August 22, 2020 by DomJ

[Lebro]

Check out the connections to the fuse on the ignition side.  The stabiliser failing would not effect wipers etc.

Bob.

Bob.

[DomJ]

Thanks Bob - this is something that has confused me about the wiring diagram - I now realise that the other part of the circuit continues off the ‘B‘ terminal on the stabiliser (the way it’s shown on the diagram at least) and it’s just the instruments mentioned that are fed off the  ‘I’ terminal. I did check the feed on the fuse box using a multimeter today but I’m beginning to wonder now if I was checking the right fuse ... Unfortunately, I’m still finding my way around the electrics but learning a bit more each time something new goes wrong...

[Rob Salisbury]

It's also worth checking and cleaning the fuses and their contacts in the fuse box, on an un-modified TR4A there are only 2 fuses to check.

cheers Rob

[BRENDA1]

I had similar problem with my 4a and found that the fuse holders were loose and if you took the fuses out altogether you could move the holders in the base, I replaced the fuse block and all was well. Since then I have changed some of the wiring and installed a modified fuse block and relays under the dashboard.
 

Mike Redrose Group 

[RogerH]

There have been issues where 'cold' fuses check out OK but after some use they may go open circuit inside the glass tube.

Throw the fuses away and fit new ones. (assuming you are using glass fuses).

 

Roger

[keith1948]

The subject of fuse ratings came up back in 2013. This was my note to CVTR and on the forum from that time

 

On page 40 of issue of TR Action no 267 is an article on new fuse ratings and risk of setting fire to your TR's wiring loom with new fuses. In Halfords you can buy glass fuses that look similar to the original lucas type BUT the power rating of eg 25 Amp is the running ampage not the blow ampage as in the older lucas parts. This is the reply (in BOLD) I received from Halfords technical dept for my enquiry (in normal text):

Customer asks:

"Older glass fuses were usually marked with a continuous and a blow rating
eg 12 Amp continuous blow at 25 Amp. NOT MARKED IN THIS WAY NOW  
Fuses to the newer SAE standard are rated by their running current ie. 25
Amp running blow at much higher power. YES ALL OUR FUSES BLOW HIGHER THAN
THE RATING.
I have read of two people with classic Triumph TR's fitting what they
thought were fuses with blow ratings of 35 Amp were in fact to the newer
specification SAE of 35 Amp running power. This lead to fires in the wiring
looms of these cars because the wires were melting before the fuses blew.
What is exactly the specification of the glass fuses (HFS 146), 25 Amp blow
or 25 Amp continuous? 25AMP CONTINUOUS THEREFORE BLOWS UP TO 200% HIGHER
You also sell a multipack, HBB 102. What is the spec for these?" 
ALL FUSES THAT ARE MARKED WITH A AMPERAGE ARE CONTINUOUS AND WILL BLOW UP TO
200% OF THEIR MARKED AMPERAGE.

"The customer needs to look at what the continuous he needs and the maximum
blow, for instance if he is looking for what used to be a 17.5 amp
continuous fuse 35amp blow I would use a 15amp fuse which would blow at a
maximum of 30amps, but suggest consulting a Auto electrician for advice."

Tr's 2-4A use 25 amp blow fuses in the fuse box with a 35 amp in-line blow for the horn of the 4/4A. Not sure about other models but check handbook. You can get replacement fuses to the older spec fom Leamoco who have outlets on Althorpe St , Leamington Spa; Avenue farm Ind Estate, Stratford upon Avon; Vale Park Ind Estate, Evesham; Swan Ind Estate, Banbury. See www.leamoco.co.uk

The fuses are branded Durite www.durite.co.uk from Gordon Equipments in Harwich, Essex.

The 25 amp blow (12.5 amp continuous) are 32mm long, part number 0-374-25 and are approx £2.76 for a pack of 10.

The 35 amp blow (17.5 amp continuous) are 32 mm long, part number 0-374-35 and are the same price.

These fuses are a bit longer than the Lucas original but fit fuse holders OK.

DO NOT FIT HALFORDS 25 AMP OR 35 AMP FUSES BECAUSE THEY BLOW AT 50 AND 70 AMP! IF YOU MUST USE HALFORDS THEN USE A FUSE APPROX HALF OF RATING YOU NEED.

You have been warned!

Keith

[keith1948]

2 hours ago, BRENDA1 said:

I had similar problem with my 4a and found that the fuse holders were loose and if you took the fuses out altogether you could move the holders in the base, I replaced the fuse block and all was well. Since then I have changed some of the wiring and installed a modified fuse block and relays under the dashboard.
 

Mike Redrose Group 

Ditto

Keith

[peejay4A]

1 hour ago, RogerH said:

There have been issues where 'cold' fuses check out OK but after some use they may go open circuit inside the glass tube.

Throw the fuses away and fit new ones. (assuming you are using glass fuses).

 

Roger

This happened to me. Some fuses of doubtful quality have the fuse wire trapped between the glass tube and the end cap rather than soldered. Failure is guaranteed eventually and it’s usually intermittent and gives precisely your symptoms. 

[RobH]

7 minutes ago, keith1948 said:

The subject of fuse ratings came up back in 2013. This was my note to CVTR and on the forum from that time

I and others have pointed this out several times in recent threads on related topics Keith.

The various automotive fuse formats are explained well in this Wikipedia link:

https://en.wikipedia.org/wiki/Fuse_(automotive)

Note that the original TR fuse is the Lucas type not the American SFE standard which is marginally longer and rated differently.  

The car fuses generally available from the likes of Halfords now seem to be AGC/SFE20  types which are marked with the 'continuous carry' current :

https://www.littelfuse.com/~/media/automotive/datasheets/fuses/automotive-aftermarket/glass-fuses/littelfuse_aftermarket_glass.pdf

As you say, Durite still provide the proper dual-marked types:

https://www.durite.co.uk/s/c/wiring-accessories/fuses-fuse-holders-and-circuit-breakers/fuses/32mm-flat-ended-glass-fuses

[tthomson]

Having suffered similar problems on my TR4A, I replaced the fuse block with a blade fuse system when I replaced the loom. They seem to be more reliable (provided you use decent fuses), and the fuse rating is specified for continuous use, the blow rating is double the specified rating, rapid blow is at 20% above that. The originators of Blade fuses are Littelfuse (an American company).

For some TR fuse blocks it may be difficult to find the right size fuses.

TT

[PhilipB]

Check the connections of the wires to the fuse box terminals.

I had a similar intermittant fault which came on when more load applied to the circuits. The contact can break down under higher current loads. Cured by cleaning off the wire strands (a bit of corrosion had formed) and remaking the connections followed up with a spray of contact cleaner

Phil