TR5/TR250 Installing a main breaker or fuse on a TR250/6...

[RobT]

Being a compulsive fiddler (on the TR that is) and always looking for ways to improve the Lucas electricals on my car, it strikes me that there is quite a bit of wiring under the dash that is not protected by any fuses. In particular the circuts to the ignition switch, light switch and ammeter are unfused. This seems like not such a good idea - grounding one of these circuits would be a real problem and could cause a lot of under-dash smoking, if not a fire!

So I am considering installing a main breaker or fuse (or fuses) to protect the circuits up-stream of the fuse box. At the ammeter and/or off the starter solenoid would be the logical places to install such a device.

Has anyone else had this idea too, or experience doing something similar? A switchable circuit breaker would be best, you could also use it to isolate the electricals during repairs, etc. I am thinking 50A should do the trick. Does that sound about right to folks?

Again, thanks in advance.

Rob.

 

[Guest]

Where are you thinking of switching it from? If just literally a switch under the hood then you might as well have a quick disconnect from the battery.

That said, my car (thanks to a po I assume) has a 50A fuse inline with the take off from the battery throught the bulkhead. All the hot wires are attached to that. It seems to be working just fine, so I'm not in a rush to change it.

One other option if you don't care about originality. You might want to consider taking the main current drawing circuits - ignition and lights, say - and putting relays on them. That will at least minimise the under dash current draw, allow you to upgrade the wiring to something heavier, and if you wish, put individual fuses on each circuit. I did it with my headlights. It's pretty straightforward (in fact you can buy a kit now to do just that for about $30). I'm much happier with 12 gauge wire carrying the current.

 

[Keoke]

"I am thinking that 50 amps should do the trick." Think about no more than 35 amps to do the trick.---Fwiw...Keoke /ubbthreads/images/graemlins/yesnod.gif

 

[martx-5]

If you REALLY feel like protecting things as they should be, you can go this route. /ubbthreads/images/graemlins/cheers.gif Of course, you lose all originality. /ubbthreads/images/graemlins/hammer.gif

 

[Dave Russell]

Re: Installing a main breaker or fuse on a TR250/6

I agree with Keoke. A 50 amp fuse will not protect the smaller wires. It will just let them burn. Much better to install several smaller fuses in strategic circuits. For critical circuits such as headlights, no fuse or a self resetting circuit breaker would be best. Or fuse high & low beams separately. One of the most vulnerable circuits is the one feeding the tail, park lamps, & number plate lamp. Very easily damaged in a minor collision.
D

 

[RobT]

Re: Installing a main breaker or fuse on a TR250/6

Most of the circuits to the head-lights, tail-lights etc. are already protected by the 35A fuses in the fuse box. My concern is the wiring between the battery/altenator and the fuse box. This is completely unprotected and a 50A fuse or C/B (since most of it looks to be 10 gauge)would do to protect it. (Isn't the Ammeter 60A?)

I was thinking something mounted under the dash - in line with the Brown/White line out of the Ammeter would do it. May be "boots & braces", but would give me piece of mind.

Rob.

 

[Dave Russell]

Re: Installing a main breaker or fuse on a TR250/6

Hi Rob,
Sounds ok. I thought that you originally suggested that the ignition sw, light sw, & ammeter needed to be fused with one large fuse. Sorry.
D

 

[RobT]

Re: Installing a main breaker or fuse on a TR250/6

Dave:

Yes, these components (the ignition sw, light sw, & ammeter) are the ones without protection since they are the components down-stream of the battery but up-stream of the fuse box. A short to the back of the ammeter for instance, or in the light switch could be ugly, since there is currently no fuse to "blow". Once past the fuse box, you're (relatively) fine. Perhaps I am being overly cautious, and there is little chance of a problem on these few circuits. But then again....

 

[Alan_Myers]

Re: Installing a main breaker or fuse on a TR250/6

Hi,

There are some small, self-resetting circuit breakers available. I've got a couple that have metal cases and look a lot like an old Lucas relay, scaled down. I will be using these my TR4s critical systems such as the elec. fuel pump and cooling fan.

Besides that, I'll be adding fuse-protected circuits for lights and other things. To increase the number of fuses (from two 35A) I'll using two or three Lucas double-fuse boxes, as were original on the car, and one four-fuse Lucas box such as was used on later TRs, som MGBs, etc. It's sort of a compromise between originality and improvement. Actually TR4 factory rally cars were fitted with as many as 4 of the four-fuse Lucas boxes, to handle of common modifications such as lights, electric fuel pump, etc.

I also plan to add relays (Lucas) to headlights and driving/fog lights, at least. The relays will serve to take the load off the switch. They will also interact with a relay in the headlight high/low circuits, so that a single dash switch turns the driving/fog lamps on and switching between high and low beams will select either driving or fog lamp, respectively.

Another alternative for the major leads from alternator/battery might be a fusible link.

Alan Myers
San Jose, Calif.
'62 TR4 CT17602L



All this is a bit down the road, though. There's currently no wiring at all in the car!

 

[Keoke]

"Of course you lose all originality". I take it you prefer losng the car. /ubbthreads/images/graemlins/rolleyes.gif---Keoke

 

[Keoke]

RobT, Yes I run a 35 amp circuit breaker off the starter solenoid and all lighting circuits are relay operated and properly fused. The largest additional fuse in my car is 16Amps.---Fwiw---Keoke