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Wiring in an AMPS gauge in my new dash


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#1 Prawn

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Posted 09 October 2004 - 06:48 PM

hey guys
ive just purchased a brushed alloy dash from huddersfield spares, in a 3+3 format
ive spent a large proportion of the day messing around trying to fit the dash, and ive finally got it in and secured how it should be
the only question i have, is how do i go about wiring in the auxillary gauges i have?
with the dash i purchased the sunpro 3 gauge set for 29.99, and before anyone tells me, i know these are not great quality gauges, and tehy do look pretty cheap, but if tehy work, and fill up teh 3 holes until i can afford proper ones, then im happy
now water temp and oil pressure are easy enough to plumb in
but the 3rd gauge is an AMPS gauge
i know an ammeter has to be connected in series (i think)
but which wire do i connect this to?
ive looked on the instructions but its really a bit too vague, so i thought id ask here.
i assume i break the chosen wire, and run it into the amps gauge, then back to the other end of the split???

one other question:
how do i go about wiring in the dial lights?
should i simply tap into the wire comming from the light switch? or would teh current drawn by 3 12v bulbs be too high for the switch (ive had trouble with the light switch overheating before)?
if not, should i tap into the fuse box and the wire for the headlights/sidelights? or would the current going through here be too much to put through 3 small 12v bulbs????
im relatively confident with wiring things up, just as long as i know where to start. ive got a mulitmeter to play with, so i can test whats live and whats not.
any help would be great
thanks a lot
nick

#2 Guess-Works.com

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Posted 09 October 2004 - 08:01 PM

In simple terms the ammeter, as you say, needs to be wired in series... and then will measure the current drawn of all items down stream of the ammeter...

Therefore you want to plumb in your ammeter in to the circuit to catch as much of the electrical equipment as possible..

The best place would be between the Battery and everything else, but thats not pratical, especially if you include the load which the starter moter draws... so moving down stream a little further, we arrive at the solenoid... On this the chunky wire from the battery terminates and drives all the rest of the cars electrics, and another place where the ammeter could be placed... This is where I plumbed in mine.

To do this you need... Some serious 20+Amp ( I use 2*20amp strands ) wire to hande the current which will be drawn by the electics, and an isolated junction box so you can join the returning wires from the ammeter back into the loom.


Re the dial illumination, wire them into the side lights circuit, or tap of the lighting circuit for the main 3 dial. should not overload the switch.

#3 dklawson

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Posted 10 October 2004 - 01:23 AM

While I agree with Guessworks on supplying power to the gauge lamps... I have a different comment about the Ammeter. Don't use it.

As you and Guessworks mentioned, Ammeters have to be in series with ALL the current to/from the battery (except the starter) to indicate what's happening as far as charging/draining the battery. This was OK when our cars were powered with 22 Amp generators (dynamos). Today's alternators simply put out too much power to safely pass all their output from the engine compartment, through a hole in the firewall, and back out to the battery. Dangerous stuff. Replace the Ammeter with a volt meter. On an alternator equipped car they give just as much useful information as an ammeter and they are not dangerous.

For your gauges, watch eBay. I'm VERY partial to VDO instruments. It is very common to see used and NOS gauges from them on eBay for a very good price. If you don't mind using 70 degree sweep guages, these are/were VERY common in VWs. There should be plenty of VW instruments for sale and with the proper new sending units you'll have a good gauge at the right price. I think over there you also have TIM gauges and these look to be a decent compromise.

#4 bluebottle

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Posted 10 October 2004 - 08:12 AM

i've had an ampmeter fitted to my car for years and its got an alternator fitted,and it been fine, as long as you use cable that is capable of taking the current, you should be ok, just dont go for thin cable, go for as thick as you can get , even if it means making up dummy cables to get the length, and then getting them made up at an auto electricians.

#5 dklawson

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Posted 11 October 2004 - 12:31 AM

If people insist on running an ammeter on a car with an alternator I guess it's worth mentioning as Bluebottle said, run the heaviest gauge wire you can. It needs to have as much (if not more) copper than the (combined) cables normally connected to the alternator. Of equal if not higher importance is to thoroughly protect the wires where they pass through the firewall. There should NEVER be any chance that these wires or their insulation can come into contact with a sheet metal edge. I still say a volt meter is a better option as far as safety is concerned.

#6 Guess-Works.com

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Posted 11 October 2004 - 11:42 AM

I'm just greedy, I have both in Schmoo, but What DK says about the voltmeter is true, you'll see that dropping quite rapidly before the ammeter starts to twitch if the alternator is failing... ( but also the ignition light will start to flicker )

I doubledup this wire for use on the ammeter ( think it's rated about 20A) and created a new hole with grommet for it in the bulkhead

http://www.maplin.co...ce=14&doy=11m10

#7 Dan

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Posted 12 October 2004 - 10:27 PM

There is an issue with running high current cables through holes in sheet metal, even if the currect is DC it can lead to heating of the sheet. There is a formula for working out how thick the sheet has to be and how large the hole diameter is compared to the gauge of cable and current it carries, but I really can't remember it off the top of my head. Along with the amount of high current cable needed this is one of the reasons that cars basically don't come with ammeters any more. But if you want one, just make sure you use really big cables. Bear in mind that if the instrument fails, you will have no power to anything in your car. No ignition, no brake lights, no nothing. Do you want to trust that to a cheap instrument? I wanted to fit an ammeter which cost £40.00 on it's own and I still wasn't satisfied with the quality of it (gauge reads to 60A, but is connected by 9.5mm blades which are rated to roughly 50A. Didn't trust that for a minute).

Lighting wise, unless you use a relay the load of the extra lamps will always be carried by the master light switch because of how the Mini is wired up. It doesn't matter where you connect it in. But I imagine these are about 2.2W each so combined they will only draw about half an amp. That won't matter much, but if you want to increase the lifespan of your lightswitch move the dip and main beam headlamps onto relay feeds to lighten the load somewhat.




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