Head lamp relay

[Drdogface]

Just got the Euro H4 kits but not the higher wattage bulb set. One recent post/thread advised installing a relay even though it's just the lower wattage variety. Is this really so?

What's involved in installing this realy? This, BTW, is for 78SC. Never done that before.

[Rick Lee]

Do a search for "Marcus Sucro". He's the guy who makes the relay kits. Having chaged the turn signal stalk once, installing relays was a very painless and cheap insurance against frying my turn signal stalk again.

[Wil Ferch]

Here'e the missing link for understanding what's happening...

At 80W instead of 55 or 60 watt....the power draw is proportional to the watt difference. In *either* case this ( full) power is handled by the dinky stalk switch. A relay will simply draw the small amount of power to suck in the contacts that bridge the main headlight circuit....pro'ly 1/100th the power draw compared to not using relays. At this severe reduction, it doesn't matter if the headlights are 55 or 80W...its a dramatic reduction on the switch in either case.

Wil

[Dennis Kalma]

You can put in the regular Porsche round relays as well, they of course fit the fuse panel and look "proper". Hopefully this description is accurate, but I am working off a combination of my notes, the Porsche wiring diagram and memory. I think it is right..........

Basically your headlight switch currently directs the current (with the main light switch on) to the headlight bulbs via two wires: a yellow which sends current for low beams and a white wire which directs the current for high beams. There is a relay upstream of the fuse panel which seems to be in place to allow the flasher switch to turn on the high beams rather than the low beams. It does not have an effect in this set up as it is before (electrically speaking) the relay you are going to install. What in effect you have to do is to use the yellow and white wires coming off of your dimmer switch on the steering column to switch a relay which in turn sends current to the lights and the only current going through the switch is that required to switch the relay.....which is sfa and not any strain on the contacts.

The Porsche relay's socket (901 612 333 00) has 5 wires connected to them............they are:

Terminal Function
30 Switched current supply (red)
85 Ground for switching current (brown)
86 Power for switching current (grey)
87 Switched currrent output (relay not recieving
switching curren aka default position) (red/white)
87a Switched current output (relay recieving
switching current) (red/white)

For low beam relay control.........the yellow wire which goes to the power side of S5/S6 on the front fuse panel (they have an internal
connection) goes to the grey wire on the relay. The brown wire goes to ground, pick a likely looking wire (I tied it to the big ground connection near the battery, but then again I am anally retentive and neurotic, you may want to take an easier one). The red wire needs to pick up power from another fuse on the front panel (I used S17) and supplies power to the headlights. The default (87/red and white on
relay) is free..........not connected to anything as you don't want the power from S17 going anywhere if the headlights are not on. Make sure that there are no bare wires coming out of this (I cut it short and then put heat shrink tubing over it).The other red and white (off of 87a) goes to where the yellow wire used to be, at the power side of S5/S6. Voila, relay controlled low beams!!

For high beam control, it is basically the same except that the power from the dimmer switch for high beams is white and connected to the power side of S7/S8. It then goes to the grey wire on its relay (86), brown to a ground (85), red wire to a fuse on the panel (S17 is fine), default red and white (off of 87 on relay) is not connected, other red and white (87a) is connected where white used to be at the power side of S7/S8.

Note that the power (red) does not need to have a fuse on the input side of things (ie you can connect it to the side which is closest to the battery electrically speaking) as you have 2 fuses for each headlight in S5 thru S8. Minor risk that the relay will go nuts and cook something, but I was willing to take the chance..

Note also that the plastic on the relay holder is fairly stiff and can be a pain to fit into the panel......I just boiled some water and soaked the relay holder (minus relay of course) until the heat made the plastic soft and then it popped in no problem at all. Resulting effect is that it all looks stock and is (IMHO) "right".

Hope this helps.......

Dennis Kalma

[Drdogface]

Thanks guys...much appreciated

[ianc]

Hi guys,

I was searching for the term '87a' in preparation for my H4 installation project, and found this thread. This is just a clarification for future readers of this thread:

Dennis, you made a great post, but you have the functions of 87 and 87a reversed. I was confounded when I found a post with the opposite explanation from yours, so I had no recourse but to go and measure for myself.

87a receives current when the relay is NOT energized.

87 receives current when it is (ie. there is current applied to 86).

Hopefully that will help some future itinerant wanderer...

cheers,

ianc