Electrical fault - headlights not working

[Steve G]

I have a 1970 S4 DHC. My headlights stopped working a while back, I was driving the car into the garage after an hour long drive, mostly in the rain, and there was a single 'click' noise and the headlights went out. I've checked the bulbs and the fuse and they are OK, the sidelights work, as do the brake lights, indicators and tail lights. The vacuum pods also work really well as I fixed them the year before. I have a multimeter but don't know the correct way to test for the fault, can anyone help me by giving the procedure for testing the headlight circuit? Is there something obvious (to an experienced owner, obviously not to me) that could be the cause?

Thanks in advance.

[512BB]

Rain, headlights and a click would indicate to me that there is a problem with the light relays. They are not facing forwards are they, so any water running off the bonnet soaks them?

In any event, clean up the contacts on all the relays, if they have gotten wet, dry them out, and I would think that will sort your problem.

Leslie

[oldelanman]

If neither Main nor Dip beam works I would suspect the microswitch on the headlamp pod which earths both relays.

[Steve G]

No main or dipped beam. How do I test the microswitch?

[oldelanman]

No main or dipped beam. How do I test the microswitch?

If your car is still wired as original you should have two microswitches, one on each headlamp pod. The main and dip beam relays are operated by the one on the RH pod and the flasher relay is operated by the one on the LH pod. First locate the switch on the RH pod, it should have two wires connected to it, one black/red which goes to the relays and one plain black which goes to earth. Disconnect the black/red wire from the switch, switch on your headlamps and connect the wire directly to a suitable earth point. You should hear the relays click in and the headlights come on - if so then the fault is in the microswitch itself or it has a bad earth connection (black wire) - if nothing happens when you earth the black/red wire the fault is elsewhere. Hope this helps.

[gazzamuffin]

hi oldelan man and steve G,

did you eventually find the root cause of the problem?

I am having a similar issue but dont have any microswitches so i have connected directly into the earth but still no power to the lights

[ricarbo]

Steve, I'm in Hove, just a stone's throw, and would be happy to have a look, if you'd like.
regards.
Richard.

[YellowS4DHC]

gazzamuffin,

if the problem is no power to the headlamps, I'd check the following:

1. Check to make sure your headlight switch has power to it; power should come via the Brown/Blue wire coming from the control box. I believe there is a junction under the dash where this power is channeled to both the ignition switch and the headlight switch; make sure the connections at this junction are good and that the switch has power.

2. If item 1 checks out ok, ensure that the Blue/Brown wire from the ignition switch to the hi/lo beam switch is properly connected. Check to see if the Blue/Brown wire is powered when the headlamp switch is on. If so, then check the operation of the hi/lo beam switch by verifying power is output to the UB and UN wires that run to the M and D relays, respectively.

3. If everything checks out ok to this point, you should have power to the M and D relay windings. If your headlamps still won't work, you should then check to make sure the solid Blue wire from the control box is powered and properly connected to the contact terminal of the M relay (a Blue bridge wire should bring this power to the corresponding contact terminal on the D relay).

hope this helps.

Regards
Rick


'69 Elan S4 DHC
'57 T1 Speedster
'67 S800 Coupe

[gazzamuffin]

Hi YellowS4DHC,

thanks for the info I shall take a look and let you know!!

Gazzamuffin