hi all,

I've recently picked up a 77 mk1 and the drive back at 2 am on the m6 with no street lighting and inches away from temporary crash barriers was airy to say the least, according to manual, h/lamp bulbs are 40/45w, can I just do a straight swop and fit uprated h4 60/55w bulbs or is there more to it.

cheers..

The main problem is the wiring to the headlights isn't up to the job, the wires are too small for the current and so you get a voltage drop, instead of getting 12.5v at the bulbs you'll be lucky to have 10v and just fitting 60/55W bulbs will only make the problem worse as the current will be higher and that will result in even lower voltage at the bulbs, the only real way to improve the lighting is to fit a relayed loom with a heavy duty wire to supply the relays and use the original wiring to control the relays 

thanks for the info, just spotted a ready made plug & play uprated loom & bulbs kit on fleabay, got to be worth a punt !

check first but possibly a p45t bulb...you cant just whack h4s in unless later mk2 lamps fit?

 

universal loom here...nige is bang on about the voltage it will never be good without relays

 

 https://www.ebay.co.uk/itm/H4-Headlight-Headlamp-Light-Bulb-Relay-Wiring-Harness-Socket-Plug-Wire-Kit/192284936495?epid=2194744936&hash=item2cc513492f:g:lIQAAOSwdqRalO26

I would suggest that you use 28/ 0.30 cable between the supply and the relays as well as between the relays and the bulb holders - don't forget the earth also needs the same current carrying capacity.

As Nige says, use the original wiring to the relay coils.

Another common cause of volt drop, is the fuse holders on your model, a bit more of a pain than just doing the head lights, but a modern fuse board would probably pay and overcome the unreliability of the present one.

It would be worth downloading the catalogue from Vehicle Wiring Products, this contains everything that you would need.

 

Regards

thanks for the advice & links guy's 

Yeah, P45t bulbs have same base as the old round 40watt and are available as Halogen. I use them.

 

Also check the alternator voltage with engine running at the battery. Hopefully 13.8volts. If not then the  brush pack regulator could also be replaced , even with a modern 14.2v item.

Changing to fat cable from alternator may help (may need a new Lucas plug).