9 replies to this topic

[Cook]

Hi all.  I'm looking to fit up a modern head unit and trying to understand a few thing, bearing in mind my limited knowledge.  I have installed an aircon unit so the heat/fan wiring is, I think, to some extent obsolete.  Here (I think) is a pic of the plug at the dash and where it would exit the firewall.  Not sure why the auto elec left them there. If he ever called me back I might ask him. Also here is a pick of the back of the fuse panel which shows a blue wire, which I think is the wiring for the new fan.  I obviously need a constant power source and an accessory point for the radio. My questions are:

 

What are the 3 wires on the old heater fan wiring

Is it likely that I could use any of the wires for the radio

Looking at the fuse panel, why is there no tabs in the "radio" section that would house a fuse. What would normally happen here.

 

Thanks in advance. Depending on answers will determine if I attempt this myself or not lol.  Cheers Ron 

 

  

Attached Files

•  Back of Fuse Panel.jpg   165.94K   4 downloads
•  Heater Fan Bulkhead wire.jpg   175.72K   4 downloads
•  Heater Fan wire at Dash.jpg   117.59K   2 downloads

[Rockoz]

From memory, as a radio was optional equipment, if one was fitted they would use plug in fuse holders into the space provided.

On you r fuse box you should be able to make out the fuses that are powered by the battery, those that come on with accessories, ignition and lighting.

From memory there were some spare tabs that you could plug a wire on to to get power from the relevant source.

But perhaps not every one you need.

I have used spade terminal double adaptors in the past to take power from the protected side of a fuse to power stuff up.

Generally your unit would require, battery power, ignition power and a source from the lighting circuit.

It could also need an input from the handbrake depending on what the unit does.

Personally I wouldnt bother trying to tap in to old wiring.

I would run new stuff from the fuse box and have inline fuses in an accessible spot perhaps beside the existing fuse panel.

 

Cheers

 

Rob

[Heath]

There is a spot for a "radio" fuse as described above. It's the top left fuse and it was used for a very low power draw and simple 1970's radio. It takes a 3 Amp (short) glass fuse but it looks like your fusebox is not populated with the terminals or the jumper... In my case, I raided another fusebox to grab more terminals and jumpers to populate mine with a 'Radio' fuse and also a Rear Window Demist fuse, because I wanted things to be marked similarly to the factory. 

 2020-07-14 21.37.05.jpg   274.58K   3 downloads

See the jumper that reaches from the RHS of the fusebox circuit to the 'radio' fuse supply. (tan coloured wire)

 2021-09-04 17.34.17.jpg   213.44K   3 downloads

The "Radio" circuit has the same active status as the heater fan... which is that it gets power with ignition on, or accessories. This is basically the "ON" signal for your aftermarket stereo. 

Regardless of which you use, the best practice will be to use this to not actually power the stereo, only to tell the stereo that when it has 12V, the stereo should be on (and when the 12V drops to zero, the stereo should turn off).

 

But your stereo will also need a constant 12V supply so that it doesn't lose its presets etc.

Additionally to that, if you used the standard 3A 'radio' fuse you wouldn't have enough current available for a decent stereo that actually has some grunt. Amplifiers, for example those driving decent power speakers or a sub are going to draw a lot more than the original stereo. I would run my own (fused) constant 12V supply from the battery or alternator for that purpose. It should not need to be switched on and off by the car.

 

I have a number of 12V constant power wires that connect to a firewall power post I installed, and one of them covers headlights, one covers stereo, one covers the main body loom (via the standard fuse box) engine management.

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Your aftermarket air con is probably powered in some direct way like this.

 

The heater fan supply (rated at 15A) if no longer in use, will provide a higher current ceiling (15A rather than 3A), but you'll lose all of your headunit settings (clock, display colour, what you were playing last) every time you turn the ignition off. So I wouldn't say that's a solution. If you were lazier, you could tap something off the main red cable that feeds the whole fuse box, but I wouldn't recommend stressing that original wire any more.

[Rockoz]

If you look deeper into Heaths picture of the fuse panel, you will see a spare terminal sticking up.

It may be sufficient for the battery supply, depending on its position relative to the feeds.

Any spare terminals in the middle can be utilised if they are from the right source, battery, ignition or accessories.

If I find time today I will see if I have a fuse panel amongst the parts I recently acquired.

If so will give a better answer.

But you could work it out yourself with a multimeter.

I know there are some spare terminals for extras.

But not sure what feeds them.

 

Cheers

 

Rob

[Cook]

Thanks gents.  I will get the multimeter out.  My new radio isn't anything too powerful and no amps etc so not needing massive power.  I was thinking that hopefully one of the obsolete wires from the old heater fan may still be functional to give me "ignition" power for the radio ands then just have to find a constant fed.  I can run a wire from the battery (in the hatch area) if need be, but there is a spare terminal in my panel so fingers crossed it is constant.  Cheers Ron

[Cook]

Checked with the multimeter.  I do have a spare terminal at the fuse panel but doesn't seem to have any power either constant or ignition. The brown wire from the old heater fan wiring still has ignition power so I will plug into that.  I think for the constant source I will tap into the wire for the brake pedal switch. Realised as I don't have an external aerial (welded up the hole in the guard) so I will have to use an in cabin one and seems I will also need to wire that up.  I assume this only needs ignition source so will wire that in with the orange ignition wire as well.  Any good/bad/indifferent views on various hidden aerials. Cheers Ron

[Heath]

The hidden aerials apparently work better with a "booster".
I have a very hidden aerial (a wire tucked in around the windscreen rubber) with a Aerpro (AP170) booster.

 

Barely tested it, can't tell you if it's good or bad, haha.

 

Some people have connected them to a rear screen demister with good success apparently. I did not do that.

[Cook]

Thanks Heath.  I've got it all wired up (roughed in really) and all works.  Found another spare off the horn relay for constant and used the cigar lighter plug for ignition.  Bought a cheap pop up aerial to test and currently sits on the passenger seat.  Have heard of people simply zip tying these under the dash. Have had a look at the AP170 but still trying to see if I can get anything to work that doesn't necessitate sticking to the window. I don't have a rear demister.  Cheers Ron

Edited by Cook, 21 June 2022 - 04:25 PM.

[Heath]

The AP170 is a booster thing, it doesn't have to be on the glass itself.

 

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Mine is right up the top of the photo, almost hidden behind the demist vent under the windscreen. It has a single wire that wraps around the windscreen rubber and of course everything to do with the aerial is 100% concealed, you can't see it even if you're looking for it.

 

I probably would have been just as happy with a funny 80's roof-mount aerial, but a here we are.

[77lx308]

I have simply put the aerial on top of the glovebox (under the dash) and then extended it out to behind the dash cluster as far as it would go.

Seems to do the job