Datsun Roadster Forum-311s.org

Well I getting my 67.5 1600 wiring all back to stock form since the PO made some interesting adjustments. Also, I added a 30 amp fuse that goes to my amp gauge as suggested. The issue I am having is one fog light works fine (55w) but when I hook the second one up, it blows my 30 amp fuse going to my amp gauge. I thought my draw of power should only be 10 amps from the two 55 watt bulbs. (55x2=110 / 12 volts= approx. 10 amps draw). Am I missing anything here or is a possible fog light issue? The wiring looks fine but havent really dug to much around the trouble shoot it any more since I had to buy more 30 amp fuses. Thanks.

Mine were wonky until I installed a relay for the fog lights. Now they work perfectly. Now I love relays.

You might want to investigate the possibility your light circuit is carrying additional loads. If you have an ammeter, pull the fuse and measure current draw with various combinations of lights switched on and off. This should confirm whether the "PO's interesting adjustments" were planned or experiments.

You shouldn't run the fogs without a relay. You are just asking for trouble taxing the factory harness with more amperage. As Garm suggests, use the dash switch to trigger a relay to deliver fused power from the battery to the lights.

If the left fog is blowing the fuse, what happens when you only have the right one on and then add the left? You likely have a short in the light housing or the wiring somewhere. Check your splices for a stray strand of wire. Heat shrink tubing is your friend.

THanks for the suggestion about a relay. I dont know how these work but I will investigate it. Im learning electrical as I go.

Regarding what happens to the fog lights when I hook them up, my right light works fine and then when I add the second one, it blows the 30 amp fuse leading to the amp meter. I think there may be an issue with one of the fog lights but have not confirmed it yet.

Problem: -
According to the ORIGINAL schematic, the Fog lamps are fed 12V from the L fuse in the fuse block: -
http://www.311s.org/PDFs/1967_5%20%20Da ... 20rev4.pdf
The fact that you are blowing the 30A Ammeter fuse indicates that the Fog(s) are bypassing the L fuse.
I would advise tracing the wiring to see where the PO has done this and correct it.

Briefly, relays do the hard work, allowing the switch to be relieved of high current loads.
You will still need protection[?] but the circuit is a simple one: -






You just add a conventional Bosch/Narva/Hella relay coil terminal 86 in series with the Fog lamp feed wire from the switch.
The other side of the relay coil, terminal 85, is grounded.
The 30A L fuse feed is also wired to the relay terminal 30.
That's the bit that does all the hard work.
The switch now only has to handle the minute current draw of the relay coil

If bikermike can teach ME how to wire up a relay, and he did -- trust me you can do it.

This is the coolest YouTube for learning how a relay works:

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Thanks for the input and advise. Hopefully I can figure this stuff out and button up my electrical and move on to exhaust piping.

I would also check the size of the L fuse in the factory fusebox. Maybe the PO was creative.

The L fuse should be 30A
While you are at it, check them all for proper rating.
http://311s.org/phpBB3/viewtopic.php?f= ... se#p132440

Try putting a lower fuse in the "L" spot there and see if it blows 1st. It may help your troubleshooting.

I think after I rewired my headlights and fogs to run off relays and added the ammeter fuse, I put a 20A or 25A fuse in the factory fuse box so it would blow before the ammeter fuse.

You may be better off removing the offending light and bench testing it. Hook it up to a 12V battery or a battery charger with a fuse on the + side. If it blows the fuse when disconnected from the car's wiring you have a short in the lamp. Otherwise start investigating your wiring.

Sounds like direct short when it blows a 30 amp fuse right away. I would check the lamp housing itself, make sure + and - leads are truly isolated from each other.

I figured it out. Turns out one of my fog lights had loose wire connections to the housing. Now they work. thanks for the input and I will add a relay as well. Now i need to hook up my dash and rest of my wires...

Thanks for posting all this. My car is going to resemble mike's here shortly... Get it? Shortly...

But seriously, that vid on relays was helpful but I don't know why it works. I will review their other vids but anyone have a short, concise and easy to understand favorite vid on automotive electrical basics they might suggest?

It works because the power going through and from your switch now only has to power the relay switch, which takes very little. Now the power goes directly from the battery, through the relay to the lights. Less taxing on old longer runs of wire and the dash switch then more wire full of resistence to the lights.

Another question related to my headlights and parking lights. My 67.5 toggle has an off, parking light only position and headlight only position. In headlight position, the parking lights turn off. The schematic show this is the way it was designed. I want to have my parking lights stay on with my headlights (better visibility). Other than splicing the two positions together is there a better way to do this? If I splice both wires together, I accomplish my goal but loose my parking light only ability. Thank you to the electrical masters...

Once again, you can connect a relay to the headlamp circuit so that it energises when the headlamps come on.
Wire the contacts of the relay to switch 12V to the parking light circuit.
Then as you flip the switch from PARK to LIGHTS the relay operates and the park lamps will stay on.
You might see them flick between the two switch positions but don't tell anyone and they won't notice

@Gregs672000
The relay is an electromagnetic switch.
When the coil is energised the magnetic field generated attracts an armature.
Attached to the armature is one or a series of contacts.
They are moved to alter their switching configuration when the relay is energised.
Conventionally, the symbol of a relay in a circuit should show the relay contacts as they are when the relay is not energised.
That means that you can determine what goes ON and OFF when the coil is energised.
Also the symbol should show the moving contact moves TOWARDS the coil symbol when the relay is energised
e.g. In this symbol, at rest, the contacts 30 and 87A are continuous or MADE.
So, when energised, the armature moves to BREAK 30 and 87A and MAKE 30 to 87.
It is important to realise that 30 is a COMMON and alternately switches to 87 and 87A.
Such a relay is called a CHANGEOVER relay.
However, relays are very versatile.
If you, for example, only need a MAKE/BREAK function then the 30 and 87A terminals are interchangeable.
Clear as mud, as my Technical Instructor used to say