Home Forums General Technical Help electric harness

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  • #78289
    robert2104
    Participant

    how hard would it be to fit a new electric harness. or is it something auto elictrition could or should do. would they take the job on. a lot of then only like easy jobs. thanks. robert.

    #78294
    brianw
    Participant
    Club Member

    It is one of the simplest of cars, so should be possible to DIY espcially if you get a ready made loom that fits . . I see for example https://www.autosparks.co.uk/ sell RHD & LHD looms but have never tried it so don’t know about its quality or accuracy.
    .. I think the wires to back of the car go along the drivers side of the roof ( away from the MOT welder) so threading that is probably the hardest bit .
    I believe the connectors are ” 4.7mm Lucas type” & readily available & the club sell the grey loom tape & many of the gromets, so its possible to make parts of the loom your self too , if you are confident with wire sizing & current.

    Alot of wiring problems with old cars are due to poor connections or worn switches & not the wiring its self . I recently fitted relays on the headlights . The factory switches now only switch the relay coil current, not the 20 Amps head light current, & the switch no longer get hot, & the lights are brighter.

    Fuses would also be an improvement on the original design too.

    #78295
    JAN
    Participant

    If you’re refitting an old loom, everything usually lines up as the loom has shaped itself over the years to fit into the car. A new one might not do this so you need to know where each terminal connects; an ability to read the wiring diagram is essential.

    Fitting fuses is very difficult on these cars as the looms are not designed to accept them, and a lot of redesign is needed to accommodate a fuse box effectively. For instance, different ignition circuits are fed from the the previous component; underbonnet circuits are fed from the coil and not directly from the switch, so a fuse disables everything under the bonnet. Likewise, the rear lights and numberplate light are fed from a single cable running through the headlining. If this blows all rear lights are extinguished. Realistically, each side should be individually fused so if one side fails the other is still lit.

    #78302
    robert2104
    Participant

    thanks guys. do you think i could just rewire the headlights as everything else is working. and leave the loom there. thanks.

    #78303
    robert2104
    Participant

    oh yes what amp wire should i use for the headlights

    #78304
    JAN
    Participant

    You need to find where the fault is. There is a cable from the lamp switch to the dip switch. If there are no headlamps at all, it’s likely the fault is one of those three, but more likely to be a switch than a cable. From there, there are two cables, dipped and main beam, to under the bonnet. Each then joins to two more cables, one to each side headlamp. Again, see the wiring diagram.

    Minimum cable size 28/030 for headlights.

    #78305
    robert2104
    Participant

    it is the cable the red one from the switch and the red one from the dipswitch has burnt right up to the loom. looks like a new loom . unles i could do a seperate relay.

    #78310
    robert2104
    Participant

    i think the reason the wires burnt out is either the light switch or the dip switch has shorted out. im ok on mechanical but electrics im afraid of. but thanks for your help. Brian and jan

    #78317
    member2617
    Participant

    If you do go for a loom from autosparks, be prepared for a 3 month+ wait. Good looms, but Christ they take some time. If you can, fix it yourself.

    #78319
    robert2104
    Participant

    thanks 2617 yes ill have a go at rewiring the headlamps. if not it will be auto sparks. mine has an alternator will they make the loom accordingly . thanks for your help.

    #78320
    brianw
    Participant
    Club Member

    Hmm.. Once the loom has burnt , it might have introduced more shorts inside it. & that red wire is i think in the main part of the loom. It could be the short is confined to the headlights Or may have wrecked more.

    Look carefully at the Dip switch, ( & the wires twisting into it) as a short there will burn battery live side wires, back thorugh the main light switch & wires , Yes IF that is the only damage you could put new wires to the light & dip switches …

    Start point could be ( with battery disconnected) use a multimeter to check each part of the loom for shorts & connections unplugging the bullet connectors/ switches where necessary.( Remember the courtosy light earths the light switch when the door open) . The wiring diagram in manuals , in the technical section of this site, seems quite accurate ( except my wipers are different).

    JAN is right, neat fuseing is tricky & blowing a single fuel could loose all tail lights, but hopefully it only blows if there is a short.

    For reference here is my headlight relay wiring diagram. It does use the original headlight wiring & witches but with less current in them they should last longer now. In your case you would still have to fix the shorts first.

    https://imgur.com/a/XRYWVpz ( I was wrong above, its about 10Amp for both head lights )

    28cores of 0.30mm wire ( 2mm squared area) JAN recommends as minimum for headlights is what I used ( going one size bigger would be good too) . https://www.12voltplanet.co.uk/25-amp-single-core-thin-wall-auto-cable.html give a good range of colours with tracers, & also sell a fuse holder with an LED that shows if the fuse has blown. & the relays are plug in STDT 5 pin 40 amp with an led to show its on, from ebay

    My worst connections were made with cheap crimping tools , so now I solder on the connectors , high quality crimping tools may well be better than that .

    #78323
    member2617
    Participant

    Autosparks do make a small conversion loom if needed, failing that, their looms for a dynator (or dynamator, or similar) should also do the job. Helpful bunch in technical too if you’re unsure. They are also back up and running properly, as their phone lines were off during the bloody pandemic….

    #78325
    robert2104
    Participant

    thanks gents. very helpful great help. let you know how i get on. rob

    #78353
    robert2104
    Participant

    does a sealed beam headlamp use less power than the old type bulbs. thanks

    #78354
    JAN
    Participant

    It’s dependent on the wattage: the greater the wattage, the more current is consumed (Watts = Volts x Amps). The difference in lighting capacity above the stated wattage is how efficient the type of bulb is at converting the amps into light output.

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