Classic Mini 1979 Upgrade problem

[Alex411]

Hello,

1979 classic Mini neg earth, been updated from glass fuse to blade fuses in a side entry fuse box with a few extra ports for accessories.

Everything is working fine. BUT.

I want to hardwire in a USB port which should be simple but I can't seem to get any luck. (Like everything with a classic car it takes a few attempts)

Multimeter set to DC on 12v across the battery is getting a reading. On the fusebox though, no matter where I poke I can't get a reading with the ignition on or off (this is likely down to me being uneducated) (because everything works.) tried then putting the neg sensor on the bodywork and poking around still nothing.

Ignoring all the above I thought, just wire it up to a empty port, put in a 7.5Amp fuse, its across 17amp wire, jobs good. NO.
Wired it into a fuse port I know is working put the 7.5 in that one, still nothing.

I know it's a really simple job, so I know the issue im having is probably very obvious, but I'm trying to learn to avoid paying the auto electrician £80.

I hooked up LED lights all round which are working a treat, so thought this would be a doddle!

Any advice is much appreciated, thank you, and if this is the wrong place to post apologies I shall move it.

p.s the unconnected connection in the pic please ignore, I put that back.
Thanks,
Alex

 

[R-fur]

Is your meter still working, fuse blown, got it on AC etc.

 

[Alex411]

Is your meter still working, fuse blown, got it on AC etc.

Meter works, on the DC setting, Put '12v' above, I meant '20v' it reads 12v when I put it across the battery. All the fuses are fine!?

 

[Moley]

From what I remember about my Mini (many years ago, my current Mini is a lot different!) The original fuse box had 4 fuses. Two were perm live, two ignition controled. Make sure all the wires are connected to where they are supposed ti be on the fuse box. Theres one off in tge photo. Set your meter to DC volts. Put the black probe on a bit of metalwork. You may have to scratch the metal to get a good contact. The red probe goes to the metal 'socket' that the fuse plugs into. With the ignition on all four fuses should be live. If they are not the there may be something wrong with your meter or the black probe to the bodywork isn't makjng a good connection.If you get 12v on all four fuses, turn off the ignition and try again. You should just have two live.
BTW, you could turn on the ignition on the old Mini fusebox by putting a 1p between the two middle fuse connectors.

 

[Alex411]

From what I remember about my Mini (many years ago, my current Mini is a lot different!) The original fuse box had 4 fuses. Two were perm live, two ignition controled. Make sure all the wires are connected to where they are supposed ti be on the fuse box. Theres one off in tge photo. Set your meter to DC volts. Put the black probe on a bit of metalwork. You may have to scratch the metal to get a good contact. The red probe goes to the metal 'socket' that the fuse plugs into. With the ignition on all four fuses should be live. If they are not the there may be something wrong with your meter or the black probe to the bodywork isn't makjng a good connection.If you get 12v on all four fuses, turn off the ignition and try again. You should just have two live.
BTW, you could turn on the ignition on the old Mini fusebox by putting a 1p between the two middle fuse connectors.

Got it, I shall try and better the connection to the bodywork, thank you. And I might try the penny trick one day!

I still can't figure out why the USB port wasn't getting power.. this is what's being plugged in - Durite 0-534-15 Fast Charge USB Socket +And Type C 12/24v - https://www.agmpartscomponents.co.uk/durite-0-534-15-fast-charge-usb-socket-and-type-c-12-24v/

Its got a 7.5amp fuse and is going over 17amp cable.

 

[Moley]

Where in the fusebox were you connecting the positive lead and where where you connecting the negative lead?

 

[Alex411]

Where in the fusebox were you connecting the positive lead and where where you connecting the negative lead?

I was connecting on the next empty fuse slot down that's unused. The positive I put to the side entry pin on the left, the negative to the pin on the right, didn't work (thought it would work both ways, even if I switched these wires around?) Switched them round, neg on left, pos on right and nothing.

 

[DPG]

I was connecting on the next empty fuse slot down that's unused. The positive I put to the side entry pin on the left, the negative to the pin on the right, didn't work (thought it would work both ways, even if I switched these wires around?) Switched them round, neg on left, pos on right and nothing.

Ah, so you are measuring the voltage across both sides of a fuse holder position which is only connected on one side?

Place the positive of your meter on one side of one of the fuses in use. Put the negative of your meter to a GOOD ground or batter negative. Do you get 12VDC? Or somewhere between 12 and 14V anyway.

Then switch the ignition off and ensure you have continuity between all the inputs to each fuse holder position, regardless of whether it is in use or not.

 

[Moley]

Ah, there's your problem. You've got the fundamentals of electricity all wrong. The fuse isn't positive one side and negative on the other. The fuse goes in series in the positive feed and breaks, opening the circuit, if there's a fault. The next fuse down isn't connected to anything. No power on it. Check with your meter which fuse is live with the ignition off then check which becomes live with the ignition on. Pull out the fuse that become live with the ignition on. Check which side of the fuse holder is live with the fuse out, we'll call this SW1. Turn off the ignition and replace the fuse. What you need to do is connect the black wire (negative) for the USB adapter to a good earth. You then need to put a jumper from SW1 to the empty fuse holder connection below it. DON'T just wrap a wire around, get correct crimps and a crimper. Connect the red wire to your USB adaptor to the other side of the fuse holder. Insert the correct rating fuse (see the USB adaptor instructions) into the fuse holder, turn on the ignition and you should be good to go.

 

[Alex411]

Ah, so you are measuring the voltage across both sides of a fuse holder position which is only connected on one side?

Place the positive of your meter on one side of one of the fuses in use. Put the negative of your meter to a GOOD ground or batter negative. Do you get 12VDC? Or somewhere between 12 and 14V anyway.

Then switch the ignition off and ensure you have continuity between all the inputs to each fuse holder position, regardless of whether it is in use or not.

Sorry, I thought you meant 'where am I placing the pos and neg wires for the USB port' (that I'm trying to wire in.)

 

[DPG]

Sorry, I thought you meant 'where am I placing the pos and neg wires for the USB port' (that I'm trying to wire in.)

Yes that's still incorrect. You need to go from the outgoing side of the fuse for your positive and to earth/chassis for your negative.

 

[Alex411]

Yes that's still incorrect. You need to go from the outgoing side of the fuse for your positive and to earth/chassis for your negative.

I knew it was something stupid I was doing!! Ok, that sounds pretty simple now then! So I looked at that fuse panel and thought - you need to have a neg and a pos either side of the fuse, but actually you just need a pos terminal?

 

[Moley]

That's right. The negative is the body of the car. Positive feed to one side of tge fuse. Other side of tge fuse to the USB adaptor.

 

[Alex411]

That's right. The negative is the body of the car. Positive feed to one side of tge fuse. Other side of tge fuse to the USB adaptor.

Done it! Thank you very much everyone!