johng
CCCUK Member
Fitted a relay into my main beam circuit today. A 30amp fused relay from Halfords did the job for £6, plus a few crimp connectors and bits of cable I had lying around (the power cable from the alternator is somewhat larger than necessary, but it was available). Even managed to get enough slack on the light green headlight wire to fit it into the relay without having to extend it, so nice easy job.
The wiring is pretty straightforward. There will be a diagram on the relay as below.
You need to cut the wire which goes from the dipswitch to the main beam bulbs (on my 78 it's a light green wire, not sure if it's the same colour for all years). The end of this wire which comes from the dipswitch connects to contact 85. The end which goes to the lights connects to contact 87. Then you need to run a power cable from the alternator stud to contact 30 and an earth to contact 86. The power cable should be at least 12AWG I used much bigger than this just because it's what I had.
You need to have a fuse as the power for the main beams will no longer be coming through the headlamp switch. You can either use a relay with a fuse in it (as I did) or fit a separate inline fuse. My main beams draw just under 20amps, so I've gone for a 30amp fuse.
This is the relay I got.
Halfords HEF553 Relay 12V 30A 4 PIN | Halfords UK
The wiring is pretty straightforward. There will be a diagram on the relay as below.
You need to cut the wire which goes from the dipswitch to the main beam bulbs (on my 78 it's a light green wire, not sure if it's the same colour for all years). The end of this wire which comes from the dipswitch connects to contact 85. The end which goes to the lights connects to contact 87. Then you need to run a power cable from the alternator stud to contact 30 and an earth to contact 86. The power cable should be at least 12AWG I used much bigger than this just because it's what I had.
You need to have a fuse as the power for the main beams will no longer be coming through the headlamp switch. You can either use a relay with a fuse in it (as I did) or fit a separate inline fuse. My main beams draw just under 20amps, so I've gone for a 30amp fuse.
This is the relay I got.
Halfords HEF553 Relay 12V 30A 4 PIN | Halfords UK