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Relays on the lighting circuit
Posted: Wed Oct 14, 2020 4:58 pm
by GIX 7
My son Sean just fitted two relays to the lighting circuit. Main switch was getting ropey. What a difference. If you have not done this, I recommend you get it done. Lights are noticeably brighter!
Re: Relays on the lighting circuit
Posted: Wed Oct 14, 2020 7:46 pm
by Richard the old one
Just out of interest did he use the method that I suggested in Dolly Mixture which does not require any wires to be cut?
Re: Relays on the lighting circuit
Posted: Wed Oct 14, 2020 7:51 pm
by marshman
Yes it can make a lot of difference. 45 year old wiring, old/corroded connectors etc. and of course the main light switch and dip switch contacts all add up a lot of resistance and volts drop. By passing it all with relays makes sense and helps reserve the original light and dip switches.
Did he run some new separate earth wires as well? Also worth doing as I seem to recall all the earths come together near the offside end of the radiator where the loom "T"s off. When I added relays to mine I put a separate earth lead to each side.
Also worth cleaning and checking all the connections to the other lights as well - it is surprising how dirty and corroded they can get and still sort of work!
Roger
Re: Relays on the lighting circuit
Posted: Wed Oct 14, 2020 8:06 pm
by GrahamFountain
I've just added a new fuse box under the standard one for the feeds to the light relays, which are under the dash in mine. I got sick of the inline fuse holder's failing. It's a 4 fuse unit with only 3 used, one for each of main and dip lights, and one for the fan.
Graham
Re: Relays on the lighting circuit
Posted: Thu Oct 15, 2020 3:20 pm
by GrahamFountain
Re: Relays on the lighting circuit
Posted: Thu Oct 15, 2020 9:32 pm
by tinweevil
GIX 7 wrote: ↑Wed Oct 14, 2020 4:58 pm
My son Sean just fitted two relays to the lighting circuit. Main switch was getting ropey. What a difference. If you have not done this, I recommend you get it done. Lights are noticeably brighter!
I did mine with a 4 way fuse box on the inner wing right at the front of the car (1500 so NSF). The battery lead was replaced with a sprint/1850 one with the in line take off point with two hefty feeds to the fuse box. The relays are tucked up under the eyebrows so everything is right at the front of the car, total cable length probably a quarter of the OE arrangement and one grade up on all wires. Voltage at the lights is too variable to make comparisons so I measured the losses instead, battery +ve to +ve at the lights and battery -ve to -ve at the lights. The average loss dropped from 1.73V to 0.43V, that's 1.3V extra going into the filaments rather than lost as heat in the wiring. Call it a round 10% increase in power to the lights.
Code: Select all
Off side Near side
Outer Outer Inner Inner Outer Outer
dip high high dip
+V drop 1.13 1.63 1.43 1.63 1.69 1.19
-V drop 0.28 0.04 0.44 0.48 0.22 0.23
Total 1.41 1.67 1.87 2.11 1.91 1.42
After
+V drop 0.37 0.53 0.27 0.36 0.25 0.3
-V drop 0.092 0.125 0.075 0.037 0.079 0.089
Total 0.462 0.655 0.345 0.397 0.329 0.389
Like Richard it's fully reversible.
Re: Relays on the lighting circuit
Posted: Sat Oct 17, 2020 5:31 pm
by GIX 7
No Richard
I did read it , but he was dying to use his new crimper so I kept it simple. Used bullet connectors to join the wires.
