Lights Fuse Keeps Blowing

[blaze_away]

1998 Chim 400 Fuse 10, 25 amp

The car has been laid up since march mainly due to Covid and an Eye operation preventing me using it.

In preparation for its MOT I began checking testing all the usuals in readiness. I came to testing the lights and switched on side and main beams, did a couple main/dip flicks and then the lights fuse blew. I replaced it with another 25amp fuse.
Now when I switch the side lights switch on the fuse, in diagram below, blows after a few seconds (between 1 and 5 seconds)

To diagnose where the fault is I have.

1. Disconnected all the light connectors, in the boot, to the rear lights. (blew again)

2. Removed the nearside headlamp access panel and disconnected the headlamp and side lamp bulbs (blew again)

My intention is to repeat 2 on the offside and test again.

So I ask my learned electrical wizardry friends on here.....

Is this a 'Lights' fuse or is it just 'Dash Lights & Clock' ?

What else should I be doing ?

[Belle427]

Have you tried using the dash light illumination on/off switch under the dash to see if it still blows?
May help narrow it down a bit further.
Various illumination things fed from that fuse, and the clock.

[QBee]

Is it my imagination, or does that fuse board look damp?

[Zener]

Looks like that awful engine lacquer/sealer stuff god knows why the fuse box as been coated in the stuff advice to the OP'er junk those awful fuses without the rating written on them in white they are vastly inferior and seldom meed the rated capacity/blow rating (I can see at least 7) just keep going like you are unplugging and testing dont dismiss a short circuited bulb either before going down a wiring harness breach/defect/short etc bulbs can sometimes have a manufacture fault or defect that after many heat cycles comes to light (no pun intended) short circuit , and its below the filament line seen many bulbs fail like this over the years, not helped no doubt by the market flooded with cheap quality bulbs

Edited by Zener on Saturday 19th September 09:36

[QBee]

To answer your question about fuse 10, in my 1999 car handbook, fuse 10 is 15 amps, and is Dashlights and clock. I have typed dashlights as one word to avoid any inference that the fuse covers "Dash, Lights and Clock". The headlights on my diagram are covered by fuses 1 and 20, brake lights fuse 18, beam flash fuse 17. But TVR used whatever fuse boards were to hand, so this may well be incorrect for your car.

Does anyone else think that the list of tests and blows implies that the wiring behind the headlight switch for the lights themselves is shorting to the wiring for the illumination for that switch? It is seven years since I had to fix mine, but I seem to remember it is a ribbon cable that powers the switch. A kink in the cable, or a mouse attack, could be your explanation. Pull the gramophone out and see what's lurking behind the light switch?

My car had mice behind the dash in 2013. I live in the country, have stables and horses, and the little buggers (mice, not horses) got in through the heater system and also via perished rubber gaiters around the handbrake and gear lever. That was when I met a guy called Alex (now twin-turbo Alex), who some of you may well know, who spent an entire afternoon with me pulling the interior of the car apart and soldering all the chewed wires. I had to replace both ribbon cables, and the gaiters too. He did the whole thing for free and started me on the joy of the generosity of the PH massive.

So now, when I hear of random electrical faults in TVRs I always think "mice?"

[Classic Chim]

QBee said:

To answer your question about fuse 10, in my 1999 car handbook, fuse 10 is 15 amps, and is Dashlights and clock. I have typed dashlights as one word to avoid any inference that the fuse covers "Dash, Lights and Clock". The headlights on my diagram are covered by fuses 1 and 20, brake lights fuse 18, beam flash fuse 17. But TVR used whatever fuse boards were to hand, so this may well be incorrect for your car.

Does anyone else think that the list of tests and blows implies that the wiring behind the headlight switch for the lights themselves is shorting to the wiring for the illumination for that switch? It is seven years since I had to fix mine, but I seem to remember it is a ribbon cable that powers the switch. A kink in the cable, or a mouse attack, could be your explanation. Pull the gramophone out and see what's lurking behind the light switch?

My car had mice behind the dash in 2013. I live in the country, have stables and horses, and the little buggers (mice, not horses) got in through the heater system and also via perished rubber gaiters around the handbrake and gear lever. That was when I met a guy called Alex (now twin-turbo Alex), who some of you may well know, who spent an entire afternoon with me pulling the interior of the car apart and soldering all the chewed wires. I had to replace both ribbon cables, and the gaiters too. He did the whole thing for free and started me on the joy of the generosity of the PH massive.

So now, when I hear of random electrical faults in TVRs I always think "mice?"

That’s not a bad shout and Alex,, what a guy. I never knew that so fair darn play to him. That’s amazing generosity.
Zener, bulb shorting was discussed, top banana

[Penelope Stopit]

Will wait to see if OP returns before spending any time here

These may be of some help

[Classic Chim]

Penelope Stopit said:

Will wait to see if OP returns before spending any time here

These may be of some help

Play nice

I might just study these for hours so thanks.
Very early car drawn in 1992 so probably a fair bit different from my later 2000 year car care of the later gauges fitted etc.
I have no idea though my late father would have loved these

[blaze_away]

Thanks guys

A few answers....

The wetness is just me doing a light WD40 spray to help pull & fit fuses, (its now dried off) no water present thankfully, no mice either,

I am making progress though, its something to do with the dash lights switch.

I replaced the fuse with a 15 amp one, switched the dash lights off and tried again, partial success, main and dip beam now come on.

Sidelights are an issue, rear's work fine, fronts neither side comes on.

Pulled the stereogram out and felt the wires, no kinks in the ribbons and all seemed secure.

Picture of the dashboard switch.



Wiring diagrams I'm sure would be useful, I only wish I could understand them, I look at them to be honest I am bemused.

[Classic Chim]

If dash needs to come off give me a shout. Hopefully not but I’ve done it before Frank, it doesn’t take too long.
Stereogram

[blaze_away]

Classic Chim said:

If dash needs to come off give me a shout. Hopefully not but I’ve done it before Frank, it doesn’t take too long.
Stereogram

Cheers Alun, have had the dash top off several times. Have fitted wing nuts so its only a 10minute job now.

[Penelope Stopit]

Mmmm, tis a difficult one

25 Amp blows but 15 Amp doesn't

There is the possibility that the short is no longer on the circuit because it was on the sidelights circuit earlier and has now developed into an open circuit sidelights cable, could be somewhere between fuse-box and sidelights

or

The short is no longer on the circuit because it has been disturbed and there is also something wrong with the sidelights

If the short comes back on the circuit, try wiring a 21 Watt bulb across the fuse holder terminals instead of a fuse, bulb will be fully illuminated when short is present and will show a dim glow or extinguish when short is not present

Using the above method you can keep checking the bulbs brightness while moving the loom in places and disconnecting things

Don't place hot bulb on seat or carpet, place it on a block of wood or hang it out of the window

[Penelope Stopit]

Classic Chim said:

Play nice

I might just study these for hours so thanks.
Very early car drawn in 1992 so probably a fair bit different from my later 2000 year car care of the later gauges fitted etc.
I have no idea though my late father would have loved these

They've all been posted here in the past many times over

Am the same as your dad, love drawing and looking through diagrams, done it for most of my life

Yes, get studying, they reach parts of the brain that other drawings can not reach

[blaze_away]

Penelope Stopit said:

Mmmm, tis a difficult one

25 Amp blows but 15 Amp doesn't

There is the possibility that the short is no longer on the circuit because it was on the sidelights circuit earlier and has now developed into an open circuit sidelights cable, could be somewhere between fuse-box and sidelights

or

The short is no longer on the circuit because it has been disturbed and there is also something wrong with the sidelights

If the short comes back on the circuit, try wiring a 21 Watt bulb across the fuse holder terminals instead of a fuse, bulb will be fully illuminated when short is present and will show a dim glow or extinguish when short is not present

Using the above method you can keep checking the bulbs brightness while moving the loom in places and disconnecting things

Don't place hot bulb on seat or carpet, place it on a block of wood or hang it out of the window

Good stuff thanks everyone,

wrt to above I have ordered a couple of bulbs and a holder so I can make up the test rig suggested (is one of these ok for the job Lucas 12V 60/55W Watt H4 Halogen ?)

I will check for current at the front side lights just on the off chance they have both blown.

Have poured over those circuit diagrams and I can't find the light switch and dash light on/off switch. (Not surprising really only got one good eye at the moment, in June hospital blinded me in my left eye, had an op to fix it but its still not there yet, so a bit hampered in the visual accuity stakes)

[Penelope Stopit]

That's a coincidence

Have also been looking for the side/head switch, was aware that some circuits could be missing but have never spotted that one before (first time looking for it)

At present am working on getting those 2 halves joined back together (they don't fit side by side), have had to make adjustments to the image sizes and even then have much deleting and re-drawing to do. All being well will add a side/head switch

The best you can do is follow the Red/White cables around the diagram

Bad news about your eye, hope it recovers

No, a headlight bulb could burn the short off, similar to fitting more and more fuses

Here's a holder https://www.autoelectricsupplies.co.uk/product/449...


Here's a bulb https://www.autoelectricsupplies.co.uk/product/518...


Good luck in finding the short

[Belle427]

blaze_away said:

Thanks guys

A few answers....

The wetness is just me doing a light WD40 spray to help pull & fit fuses, (its now dried off) no water present thankfully, no mice either,

I am making progress though, its something to do with the dash lights switch.

I replaced the fuse with a 15 amp one, switched the dash lights off and tried again, partial success, main and dip beam now come on.

Sidelights are an issue, rear's work fine, fronts neither side comes on.

Pulled the stereogram out and felt the wires, no kinks in the ribbons and all seemed secure.

Picture of the dashboard switch.



Wiring diagrams I'm sure would be useful, I only wish I could understand them, I look at them to be honest I am bemused.

Looks like someone’s been meddling before, I’d expect to see the red/white and white/red wires there but not the other one.
I can send you some good wiring diagrams kindly sent to me a while ago if you pm me.

[Steve_D]

I'm going to assume you have the lights switch with ribbon cables.

Before I continue can you confirm the headlights also stopped working when fuse 10 blew? I believe they will.

I can also understand your confusion with the commonly available wiring diagrams (posted earlier by Penny) as they are crap. They show connections all arriving at connectors (example 'Block C' or 'Block F') but do not show what happens beyond that connector so are useless in understanding the full circuit path. Those connectors are for the most part on the back of the fusebox so you are not seeing anything about how the relays and fuses function. This is why I drew my own. PM me if you want a copy. It is (currently 14 pages) broken down into circuit areas so all the lighting is on one page.

Fuse 10 supplies the lighting module behind the dash it does not supply the headlights directly or headlight flash but it does supply the coils in the headlight relays. What it does supply is the sidelights, dash illumination (via the kill switch under the dash) illumination for window switches fag lighter and radio plus the biggest single user the rear fog light.

I, and others, have found this supply wire has been getting very hot with melted insulation. I have no idea why as I can count only about 100W going through there which makes about 8Amps. My guess is that something may not be right in the electronics of the module.

The module is controlled by the lights switch and the fog switch both via ribbon cables.

Steve

[QBee]

I was chasing a fault on my Saab’s front sidelight wiring in March, only to find that it was simply two blown bulbs.

[Steve_D]

blaze_away said:

Picture of the dashboard switch.

Have you tried disconnecting that switch. As said It is most definitely wrong or unusual. would normally be W/R in & R/W out so have no idea where the red is going.

Steve

[Zener]

Remove that heavier cable from that switch and report back