The Triumph Dolomite Club - Discussion Forum

Hello all!

Somewhere on here, someone mentioned to me about getting relays fitted, to help stop me melting indicator stalks, but for the life of me I can't find it? Could someone please explain to me what relays actually are, and what I need to do, so that less power goes through the switches please?

Many thanks!

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HQentity (Kyle)

1975 TRIUMPH DOLOMITE 1850 in Honeysuckle (Nina) 2015-2020


"The harder the conflict, the more glorious the Triumph." - Thomas Paine

Hi Kyle, Here is something I did for the mag; a few years back.
The explanation of how a relay works is in the text at the top right.
On SWK the relay is mounted at the base of the steering column which is very convenient.
HTH,
Tony.

That's a very good diagram Tony. The point is this Kyle, when you switch on the headlamps, or switch between dip and high beam, you pass around 10 amps through the switch contacts. (two 60 watt bulbs, 12 volts, 120/12=10). That is a lot of current for small contacts. It was OK when they were new, but over the years the contacts burn and eventually fail.

When you put a relay in the circuit, it is the relay that handles the high current, and all the switches are left to do is energise the relay which only takes a milliamp current. And if the relay should burn out (I've never had one fail yet), it is a cheap and easily replaced component.

On my Dolly I have the relays fixed to the inner wing panel just next to the battery. A nice meaty wire feeds them with power from the fuse box not far away.

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

Thats a nice easy diagram to follow,but thats for head lights,Kyle is saying his indicator stalk is melting,cant see how that would be, its only the horn that draws current

I'm a very angry driver...

The headlamps generally caused the trouble, and melted the plastic for he full beam and dipped beam. Last summer I got home by holding the flasher down until smoke came out, because everything else no longer worked. Thank you very much for your explanations! I will give it all a go shortly. Hopefully I get it correct!

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HQentity (Kyle)

1975 TRIUMPH DOLOMITE 1850 in Honeysuckle (Nina) 2015-2020


"The harder the conflict, the more glorious the Triumph." - Thomas Paine

The indicator stalk is also the dip switch so it carries the full load of two or four headlamp bulbs. With two bulbs on the current is about 10 amps, double that with four lamps on. The horns probably use less 10 amps, and almost certainly no more than 15 amps. Also the horn is only momentary use, so the contact doesn't get a chance to heat up.

Kyle, I wonder what bulbs you have in the lights? Are they much larger wattage than standard? I've never heard of a switch getting so hot it smokes. Generally when they fail they just don't make contact. Could you have a short circuit somewhere in the headlight circuit?

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

Ah I think maybe I’ve found why I’m having so much trouble there Bumpa!! That would mean the relays would definitely fix the problem! I believe I have uprated, maybe 40W is it?! I know Tony will remember! But maybe that explains the issue!

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HQentity (Kyle)

1975 TRIUMPH DOLOMITE 1850 in Honeysuckle (Nina) 2015-2020


"The harder the conflict, the more glorious the Triumph." - Thomas Paine

I seem to remember Kyle's inners are the Lucas 75W halogen units, same as on mine. I've only seen one other Dolomite with the combination and they give a fantastic view of the road ahead at night.
But of course the price you pay is a lot more current through the stalk.
My personal opinion is that the cold-filament inrush current is what kills off the Dolomite stalks. It may be for only a short time but the arcy-sparky at the switch contacts erodes the metal , leading to increased contact resistance which generates more heat and the whole lot melts.
Tony.

Standard halogen headlight bulbs are 55w each for dip beam and 60w each for high beam, so with both dip and both high beams lit up you have 230 watts, a current draw approaching 20 amps. You can get bulbs up to 100w but I don't think they comply with the regulations.

EDIT - as far as I can see there is no maximum wattage stated in the regs. I thought there was. But if you have 75 watt bulbs, they will certainly give ancient switches a hard time.

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

In a 4 headlight car with halogen bulbs, you are running (legal max from my data, but up to 100/80s are available) a 472 bulb in each of the outer lamps which is 55w dip and 60w main, and in each inner, a single H1 bulb of 75w which is only used on main beam.

So on dip, the headlamps are drawing a middling 9+ amps (55x2/12 = 9.166+)

But on main beam the draw is a whopping 22.5 amps (60+75x2/12 = 22.5) which is not only more than enough to melt the dipswitch but could seriously endanger the master light switch and the wiring too.

Which is why I mount my relays as close to the lamps as possible and use a single wire to power each individual filament. It also makes it possible to fuse them as moderns are fused, ie 4 fuses, 1 each for l/h dip, r/h dip, l/h main and r/h main. You can get relay holders that incorporate a triple blade fuse holder for each relay, so from each relay output (87) take 2 wires, 1 to each fuse (10a blow rate) to feed each dipped beam filament and 2 wires OUT of each main beam fuse (20a blow rate) so you can feed both filaments of the main beam on each side separately from the same fuse! Keeping the relays close to the lamps cuts down on the amount of internal resistance in the high draw wires and also the amount of expensive fat wire needed! My system also means you don't need whopping big fuses for the relays, you can run them unfused.

Here too, I must pick a quick bone with Tony, for his suggested use of the 35 amp glass fuse to power each relay. It's a simple and cheap solution as it lets you use another Dolomite type 2 fuse box for the headlights. But although these fuses are rated at a BLOW rate of 35amps, the continuous current rate is only 17amps, less than the 4 main beams are drawing in service! This is a point that everyone would do well to note, when picking fuses to do a job, select a fuse with a blow rate approximately double the projected current load on the circuit, as it's not only old fashioned glass fuses that work this way, ALL fuses are designed with a blow rating and a continuous current rating, the blow rate being roughly double the continuous rate!

A little bonus from this, is that you can take a loop from the switching lead (85) of the dip beam relay to the 3rd fuse holder and use it to power your rear foglight switch in the modern manner (ie, it will ONLY work on dipped beam) It does no harm to the switchgear to run the foglight without a relay as the draw is only a miserable 3.5 amps (2x21/12 = 3.5) plus another smidgin for the 3w warning light in the switch if you are being picky!

Steve

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'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
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Ok, I'm definitely getting there, thank you! I still don't fully understand how the indicator stalk switches affect the circuit for the headlamps in Tony's diagram - if you turned, say, the main beam headlights on, why does the power across the 30/87 main beam relay care?! Where is the power in that circuit coming from, is it not a closed circuit, earth to stalk?!

Thank you so much Steve! a few thoughts:

You're obviously always going to need to power the headlamps from the battery, but what we're trying to do is not make it go through the stalk, but instead send it (through a separate fuse) straight to the headlamps from the battery. You suggest individual fuses per filament to troubleshoot future issues (instead, say, one 20a fuse for two dipped beams).

Do you need "high draw" wire on the lamp side of the relay, but not the battery side? Is it not still carrying the power? Are you saying about mounting the relay close to the headlamps so most of the wire is just "low draw" wire to the stalk?

Do I need to change the thickness of the wire to something that can take more power when fitting relays? Do you buy cable based on wattage?

By the way I'm still not on halogen bulbs, but the concept is the same right, so long as I work out the values correctly based on the wattage for the fuses? Same relays (two HEF555's?).

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HQentity (Kyle)

1975 TRIUMPH DOLOMITE 1850 in Honeysuckle (Nina) 2015-2020


"The harder the conflict, the more glorious the Triumph." - Thomas Paine

Slightly different question...is it illegal to have 4 outers rather than 2 eg all 4 on dipped and all 4 on main ?
Thanks, Richard

No I don't think so, as long as there is no dazzle to oncoming drivers. Plenty of moderns show four lights all the time.

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

Kyle, I can't help thinking that you haven't quite grasped how the circuit works as standard. The way the cars were wired up from new is this. Power straight from the battery goes to the main rotary light switch. In the sidelight position power is passed through the switch to the four running lights, the number plate lights and the instrument lights.

When you click round to the headlight position, in addition to the sidelight circuit which remains "on", power is also passed to the indicator/dipswitch/horn stalk. The position of the stalk determines whether the dipped or main beams are "on" and the power is passed through the stalk contacts to the appropriate bulbs. So all the current needed to power the headlamps, side lights, tail lights, number plate lights and instrument lights is passing through both the rotary main switch and the dipswitch. Then if you press the horn, you increase that amount of power, albeit only momentarily. The indicators don't come into this system because they are fed separately from an ignition controlled circuit.

By putting relays in the circuit all that power is passed through the relay from the new thick wire feed you have to install from the battery to the relay terminal 30. Now the rotary switch and the dipswitch only have to energise the relay which is a matter of milliamps. The relay then sends the high power on to the lamps from terminal 87.

I think it would be best if you liaised with someone who can help you if you are going to install relays. Dealing with high current loads needs care.

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Mike
(1969 MGB GTV8, 1977 Dolomite 1850HL, 1971 MGB roadster now all three on the road)

Oh dear Steve! Sounds like I might not have grasped it then from your response! I thought I had it, everything you've just said makes sense?

It's just that I can't figure out what a relay is, or how the indicator stalk remains connected to power - if power only goes through the circuit powering the headlamps themselves, how does the indicator stalk ever have current, why aren't the headlamps just permanently on? The circuit for the stalk is not connected to the battery when there's a relay involved, it simply is a straight wire to earth (through the relay), and that's it? Unlike the headlamp circuit, which looks to be connected to the battery directly (through the relay), then earths itself, completing the circuit?

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HQentity (Kyle)

1975 TRIUMPH DOLOMITE 1850 in Honeysuckle (Nina) 2015-2020


"The harder the conflict, the more glorious the Triumph." - Thomas Paine