P38A Switches

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Grrrrrr said:
I did look in Maplins at relays but the smallest they had was 10A which I assumed needed a fair tug to pull it in. May have another look.

Switch is here already! Here's piccy of the back. I expected all ground to be on 1 side but apparently they're not. The bottom right one that is obscured here is also black and presumably ground.

Looks like a judicious snip would sort the tell-tale issue? Just need to work out which number is which.

View attachment 98137
Click to expand...
10A would be the switch side current not the coil current surely??

Got a linky so we can check the spec?
 
I would do it one of the 2 following ways:

Extra%20Relay.jpg


I am making the presumption that you have a cruise control switch already that is populating the cruise control hole in the dash and using the connector - if not, then you can use the wiring loom that is there already and just tap into the 2 wires you need for the ignition 12V in and then the output which will drive the relay.

If you already have cruise control switch and the one you have bought is going into an empty slot in the dash, then you will need to tap the Red/White illumination wire, and the Black ground wires into the loom behind the fascia with the other connectors.

You would then need to run only 2 wires, one would be the ground wire from the actual switch contact (to ground the relay coil) and the other being the wire to the telltale lamp, which would join to the output of the relay contacts, to make the telltale glow when the relay is active and power going through it.

You could then mount the relay anywhere there is an ignition switched 12V feed, and then link this between the common relay contact and the relay coil.

Option 2 means you run an ignition switched12V feed to the dash switch. You could then join the output of the switch with the telltale lamp, and run that wire back to the relay coil. The other side of the relay coil would need to be grounded, and then also the 12V ignition feed to the relay contact to be switched.

The main difference between the 2 options is that Option 1 will have the telltale illuminated when there is power coming through the relay to the sensor unit. Option 2, the telltale will be on as long as the switch has power and it turned on. It won't necessarily indicate there is power going through the relay. (it's unlikely the relay would fail - but if it did, the telltale would still light - whereas with option 1, it wouldn't.

Hope this helps,
Marty
 
No Saint, 10A isn't the switching side but I had no idea what the switching current is. I went back this evening and got a 30A automotive one. It reckons the switching resistance is 80 ohms. If my Ohms Law is right then that's about 1/8th amp. Pretty sure the switch will handle that. I probably out to work a fuse in somewhere too.

Thanks, Marty. I'll go with the top one. I had no cruise control switch, just a blanking plate and the one I received today. The back of the switch is already wired up as per your top image so I can just solder into the remains of the wires.

Just got to try and remember how that centre console undoes now! Back to RAVE ...
 
MrGorsky said:
1,3 and 4 Black wires are the earths.
2 is Red/White and the feed for night time illumination.
5 is White/Yellow and the "switch" positive side.
6 is Ornage/White and the telltail positive side.

If you're going to use it like a switch, you need to cut the wires from Pin 3 and use them as your negative side of the switch.

And then join 1 back up to 4 so there is an earth for the telltail and nighttime illumination.
Click to expand...

Now for the stupid question of the day: how come all these relays have 30, 85, 86, 87, 87a as the connector numbers? Seem pretty random numbers.
 
Just seen Mad Hat Man's guide to relays in the common faults and questions section. Should I put a diode somewhere to stop EMF kickback? Wouldn't it be built in to an automotive relay?

Switch is in but ran out of light before I could route power through the bulkhead.
 
Some automotive relays have them already built in - all the standard P38 ones in the underbonnet fuse box have suppression built in.

If you haven't got one with it built in, then it is worth putting one in parallel with the relay coil.
 
I must have cocked something up. Nighttime illumination isn't working and neither is the tell-tale, although the switch and relay works fine. Swear I spliced in the same colours to each other.

Going to have to take the whole lot apart again. :(
 
Grrrrrr said:
I must have cocked something up. Nighttime illumination isn't working and neither is the tell-tale, although the switch and relay works fine. Swear I spliced in the same colours to each other.

Going to have to take the whole lot apart again. :(
Click to expand...
Are there bulbs in there?
 
The lamps are accessible from the side of the switch - you don't need to disassemble any of the switch itself to get them out.
Entirely possible that they were both blown when you got them. If they are gone then let me know what colours you need and I'll see if I have some kicking about. I have a stack of them somewhere that I've put aside from when I've taken them out of switches that I've LED converted.

If I have ones you need then I'll post a couple to you.

Marty
 
martyuk said:
The lamps are accessible from the side of the switch - you don't need to disassemble any of the switch itself to get them out.
Entirely possible that they were both blown when you got them. If they are gone then let me know what colours you need and I'll see if I have some kicking about. I have a stack of them somewhere that I've put aside from when I've taken them out of switches that I've LED converted.

If I have ones you need then I'll post a couple to you.

Marty
Click to expand...

That's very kind of you. The nighttime look green and the telltale orange unless that is a filter. Will try to pop the switch tomorrow if the missus is back before dark.
 
There should only be one red/white wire in there and black wire - shouldn't make a difference as they all ground back to the same place.
The Red/White (from memory) also splices together/jumpers from one switch to the next - so if some of them light up, then the rest should aswell.
The telltale, well probably a blown lamp...

If you have others blown aswell, then send me a list of them and I'll see what I've got. It's one of the reasons I went LED in mine as I couldn't be arsed pulling the dash apart every time one blew and needed replacing!

They are all standard white lamps, with colour caps on the top - I changed the colours around in mine, so I can't remember what the factory telltales are!
 
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