Headlamp relays and fuses

Tom W

Tom W

Active Member
Hi All,

As I've upgraded the headlamps to modern bulbs. I've decided it's time to fit some relays rather than chancing that the original fuse box doesn't self combust. I'm going to add fuses to the new feeds for the headlamps too. Question is, what's the best way to go about it?

Option 1 is fit fused relays.
Advantages are the wiring will be simpler, blade fuses are reliable, and it will probably work out the cheaper option.
Disadvantages are the fuses won't be that accessible as I plan to hide the relays in the space behind the headlamp bowls to keep the engine bay looking standard. It also means carrying 2 sorts of spare fuses.

Option 2 is fit a fusebox like this: http://www.holden.co.uk/displayProduct.asp?pcode=37521
Advantages are that it takes the same sort of fuses as the main fuse box. Also, I don't think this will look out of place screwed to the inner wing, so it will be placed more accessibly.

Disadvantages are that it's probably not as reliable as modern blade fuses. There will be more joints in the wiring and I'm unsure of the quality of the cheaper versions of this available. It also works out quite expensive too, as I was planning on fitting one each side.

I was favouring option 2, but now I think about it, I'm leaning more towards option 1 again, as this will actually look most period with all the additions hidden out of the way. What does everyone else think of this?

Thanks,

Tom
 
If option 1 means using fused relays like this http://www.ebay.co.uk/itm/12Volt-30...arts_Vehicles_CarParts_SM&hash=item415c91bd65, I would be worried about water ingress (unless you put the realys in some water-tight box)?

:?: :idea: What about using in-line fuses on the output of the relay that goes to the headlamps?

:?: :idea: Is there maybe room near the existing fusebox above the glove compartement to put a box with all the fuses/relays? This would keep it hidden, safe and mean that you use existing wiring out to the engine bay?
 
I've fitted un-fused relays to the inner wing under the bonnet then used in-line fuses like these

in-line fuse holder

in the supply line, which I've taken straight from the main alternator feed to maximise power to the lights. I've only put relays in the inner main (75W) and outer main lines though as I don't believe the dip beam causes a problem in the fuse box.

Dave
 
I am actually doing this today and have opted for the fused relays, but then my engine bay doesn't look standard anyway so I am not too worried if you can see/access them.

I am using two each side, one for the dip beam and the other for the mains. One side will run both outer main beams and the other side will run both inners..

Richard
 
Potential water ingress asside, I do like those fused relays, that's a really neat solution. Never seen them before.

On the basis that the fuse only protects the circuit after the relay, I would suggest putting them as close to the supply as possible (i.e. the fusebox/live feed), so the cable runs down to the lights are protected. But that all depends how easy it is to access the wiring.
 
Dave3066 said:
I've only put relays in the inner main (75W) and outer main lines though as I don't believe the dip beam causes a problem in the fuse box.

Dave
Click to expand...

The dip beam circuit has a separate fuse for each lamp so this makes sense. My bulbs are a different wattage to the originals though, so the outers put a greater load on the circuit. The original outers are 12W 37.5/50W according to the manual. The new bulbs are H4 12V 60/55W. Does anyone know which wattage filament is for which circuit in these? I suspect the main beam is the 37.5W and the dipped is 50W based on the original fuse specs (15A for both main beam outers and a 15W each for the dipped beams). Either way, the new bulbs are putting a greater load on the circuit, so I'll need to check this out. As for the inners, they were 75W, now they have H1 55W bulbs, so the loads actually reduced.

Good point about the fused relays being vulnerable to water ingress, those are sort I was thinking of using. I don't think the fused relays fit within the standard waterproof fuseboxes either. I've considered adding a new fusebox and relays into the glove box, but thought the best idea would be to site the relays nearest to the lights to reduce the length of the high load cables.

Cheers,

Tom
 
Yes, electrically speaking, having the relays next the headlamps is a good idea (provided you have a suitable +12V of suitably gauged wire to feed them). I had a quick look to see if you could get fused 12V relays with covers that fit over them. However, I couldn't find any.
 
Tom W said:
Does anyone know which wattage filament is for which circuit in these? I suspect the main beam is the 37.5W and the dipped is 50W based on the original fuse specs (15A for both main beam outers and a 15W each for the dipped beams).
Click to expand...

I think it's the other way round Tom. The brighter filament is the main beam.

Tom W said:
As for the inners, they were 75W, now they have H1 55W bulbs,
Click to expand...

Why have you reduced the wattage of the inners? The 75W inners are great and should provide more than enough light output (unless they are damaged in some way?), and certainly more than 55W H1s. Of course I could be wrong due to better reflector design of modern headlamp units and the halogen effect. Be interesting to see photographs of the 75W and 55W halogen beams in the dark for comparison.

Dave
 
When I got the car, one inner and one outer were blown, so I decided it was a good opportunity to upgrade. At the time I bought the bulbs, I wasn't aware of the difference in wattage between the old and new, just asked the motor factors for bulbs to fit the bowls. Still new to the car back then, and hadn't joined the forum yet. I don't know about the difference between the old and new, as I never drove the car with the old, but the new set-up is really bright. I've kept the old lamps that work, so I could swap out one side for the old ones to do a comparison photo. I could fit more powerful H1 bulbs if I have made things worse.

If the brighter filament on the outers is the main beam, then Rover's size of fusing doesn't make sense. main beam outers run through one fuse, so that's 8.3A draw (50W+50W)/12V. So 15A fuse is OK. Dipped beam have a separate fuse each, so that's only 1.14A per fuse 37.5W/12V. In this case, 15A seems overkill. Would make sense to have the brighter filament for the main beam though. :?
 
From the circuit diagram for my car

Fuse 15-16 - 10A Headlamp RH dip
Fuse 17-18 - 10A Headlamp LH dip
Fuse 13-14 - 15A Headlamp main outer
Fuse 11-12 - 25A Headlamp main inner

Also 37.5W with 12V is a little over 3A, not 1.14. (I = W/V or 37.5/12 = 3.125A)

Dave
 
You're right about the current there Dave, don't know what's gone wrong with my maths :? :oops:

Seems fuse spec changed over the years though. Yours matches the 1972 diagram in my workshop manual, later cars are listed as:

Fuse 11-12 25A headlamp main beam inner
Fuse 13-14 15A headlamp main beam outer
Fuse 15-16 15A headlamp dip beam RH
Fuse 17-18 15A headlamp dip beam LH
 
I wonder why they increased the fuse rating then?

10A is more than enough for even a modern 55W dip beam. 15A is overkill as you say :?:

Dave
 
The side lamps and tail lamps have their own separate fuses, one per side, so I really don't understand Rover uprating of the fuses.

Based on the points raised above, and what's been covered on here before, I'm currently now favouring the following plan:

1.Fit an additional fusebox behind the dash, as close to the ammeter shunt as possible, whilst still being accessible for changing fuses.
This will need at least 6 fuses, 3 to replicate the 3 originally in the headlamp wiring, 1 spare for foglamps in the future, and 1 each for relay upgrades on the heated rear window and heater motor.
2. Run a large live feed cable from the shunt to the first 4 fuses in the fuse box.
3. Run new wires from the first 3 fuses down the inner wings, as per the original headlamp wiring (the fog lamp wiring can be added later should I choose to add them).
4. These wires will feed 3 relays each side (one per filament) hidden in the spaces behind the headlamp bowls.
5. The original headlamp wiring and earth connections will be used for the switching of the relays.
6. New earth connections will be made for the headlamp bowls in the area behind the headlamps.
7. The feed for the 2 fuses controlling the heated rear window will be run from the shunt through a large capacity relay.
8. The switching for this relay will be taken from the ignition switch so these circuits are only live when the ignition is on.
9. Feeds and earths for the heated rear window and heater can be added in a similar fashion to the headlamps.

This plan fulfils my criteria of not chopping about at the original wiring and doesn't leave any of the original wiring redundant. I'm not keen on leaving redundant original wiring live in the engine bay, even if it is insulated, and I don't want to go snipping any of it out. It minimises the length of any new unfused wiring on the car and it removes all of the high load items from the original wiring, fuse box and switching, so should improve reliability and hopefully prevent spontanious combustion.

Any thoughts?

Cheers, Tom
 
I can't fault your plan Tom. It sounds good and, as you say, it meets all your criteria. Also, if you or a future owner needs to do any electrical work or put things back to original setup, it should be quite easy to work out how the headlamps and rear heater/blower has been wired up.

The only thing I can think to watch out for is that your new earths are good ones. Carrying out a resistance test between the new earth points and the -ve battery terminal will quickly check this (sorry in advance if that's teaching Grandma how to suck eggs :) ).
 
No, that's a good point regarding the earth points. I did consider using the original earths for the headlamps and using the existing foglamp earth point for the headlamp relays. That way I could install the lights without having to add any new earths (at least until I come to fit fog lamps. I might try that initially and add more earth points if and when I fit fog lamps.

Tom
 
I've started doing a bit of investigation as to the wiring behind the dash, trying to find the best place to tap into the existing wiring. The ammeter shunt is wired in with large spade terminals, though it doesn't look like there's a spare terminal. I might be able to use a piggyback terminal, but they're not usually insulated, which I don't like. Looking at the wiring diagram, the wires with the white tracer are the ones on the alternator side of the shunt, so it's the top I need to tap into. The wiring diagram shows more wires connected to the shunt than I've found :? Maybe there's a couple tucked away out of sight? Alternatively, if connecting to the shunt isn't straightforward, I could tap into the existing main lighting feed on the back of the light switch, which uses the same large spade terminals.

Here's a picture of the shunt



It's located behind the instrument binnacle, directly behind the clock.

I've found this fusebox for sale http://www.autosparks.co.uk/product_inf ... ts_id=3051

I like the idea of using glass fuses, for consistency with the original fusebox. The fuse holders are one piece, so hopefully it won't suffer the same overheating problems as the standard fuse box. It's the only 6way glass fuse box I've found. I think I'm going to have to cut some of the bulkhead insulation material to get a flat space to attach the new fusebox.

Tom
 

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JVY said:
If option 1 means using fused relays like this http://www.ebay.co.uk/itm/12Volt-30...arts_Vehicles_CarParts_SM&hash=item415c91bd65, I would be worried about water ingress (unless you put the realys in some water-tight box)?
Click to expand...
Ive used pretty much the same relays for the spotlights on my daily rollerskate and have had no problems with water ingress... they're just cable tied to the front upper strutbrace, so although not in the direct line of fire from water, they do get damp/wet.
 
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