i'm going to run an ammeter. where is the best source to take power to feed it? is the main power that feeds the car interior taken from the smaller hot wire at the starter solinoid... like on a g.m.?

mike

nope
Main power is one of the fat red leads that is on the positive battery terminal.

It runs up through the tunnel to the ignition switch first.

Rich

so i would use that as the main power flow wire to the ammeter. then it must have a fusable link of some sort at the battery... no ???

There are no fuseable links.
I would not do it.
I would run a new wire just for the gauge so as not to disturb the overloaded wiring in the 40 year old car.

seriously

Rich

An ammeter should be wired to show current flow (charge/discharge) to the battery. Wired as has been suggested will always show discharge because it's measuring what that circuit consumes, ignoring other taps off the battery and more important what the alternator is producing. Wired correctly the ammeter would be in series, one terminal connected to the battery and the other connected to the alternator output and the four red wires. Heavy wiring and good connections would be needed to avoid creating the very problem you are trying to detect.

o.k. i think your saying one wire to the hot battery terminal. one to the alternator to complete the loop. would it go to the stator (s) terminal on the alternator. i'm assuming the 914's alternator has a (s) terminal... don't all alternators? if so what color wire is it? or is it another terminal to hook up to?

mike

The purpose of an ammeter is to monitor the charging of the battery during vehicle operation. With the stock 914 wiring, this is difficult. The difficulty can be seen below in the stock charging circuit. The alternator provides the battery charging current and vehicle electrical load current.

Ideally during vehicle operation, you want to charge the battery with the alternator and use the alternator to provide the vehicle electrical current.

So with the ammeter, you want to monitor the current going in and out of the battery during vehicle operation. With the stock arrangement below, this is impossible because the alternator is connected to the battery through the fat red wire that goes to the starter.

It is undesirable to put the ammeter in series with the starting current as this will likely destroy the ammeter when starting the car.
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To use an ammeter to its fullest, the wire from the alternator should be re-routed to connect to the battery not through the starter cable, but directly to the battery. Placing the ammeter between the battery positive terminal and the alternator and vehicle electrical load connection as shown below. This way the ammeter measures operating current in and out of the battery.
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I talked with someone else recently about and ammeter, and I can't honestly think of a reason where an ammeter is more beneficial than just reading the voltmeter.

Now, I'm not saying I know better. I'm hoping you can enlighten me as to why you want an ammeter.

this makes perfect sense to me.

i'm just weird that way i'm making up a 6 gauge panel and may or may not use an ammeter with the others. i really would like an air/fuel meter but they are just too much at $300

so far i'm running a duel cht and oil pressure but have a oil temp., voltage, ammeter and a vacuum for good measure (it was already in the car).

the more i think on this the more spokes wire up makes sense

reading the current going between the battery and alternator... not how many amps you are using but how many amps coming from the alternator (+) or being drawn from the battery (-).

i should only need to us 10 gauge wires? off hand i think that is what the O.E. wire size used from the alternator. what do these bitty alternators put out anyway 25 amp.s?

ANY input from others who have wired in ammeters???

mike

The purpose of an ammeter is to show shows direction ( charge or discharge) and current ( amps) to and from the battery. To do so, it must be installed in the main fed from the battery ( NOT the alternator) to the rest of the car, excluding the starter.
Basically, this is what you need - ( see picture) the line to the fuse box represents the rest of the wiring harness! The wires to the ammeter must be able to handle the maximum load in the car, if you really want an ammeter, get a non intrusive ( clip on DC) ammeter from Fluke or someone like that - only cost you $200!
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so neil, according to this diagram i think it is saying saying almost the same as spokes diagram except your saying to ad all the power wires at the + battery terminal except the starter.

anotherwords if the alternator feed goes to the starter hot (i still need to look it up), then i would take that feed from the alt. AND take the all the other batt. pos. (except starter) to one side of gauge and the other side of the gauge return straight to battery hot with a 30 amp fuse at battery.

what gauge should realistically be used?

mike

Yep, Neil's diagram is the same as the one I did plus he has the voltmeter in the correct place which should be right by the battery. The only issue with putting the voltmeter right near the battery is that you need to have a relay to disconnect the voltmeter when the car is turned off. I think Neil shows this with the "1A" item in series with the voltmenter. The connection of the relay would be very simple.

Which gauge are you asking about using? The voltmeter or Ammeter? To be period correct, both should be VDO gauges. The ammeter would most likely be a 30 amp unit. Auto ammeters are designed to handle heavy loads like this.

Do you have an ammeter already?






The ammeter gives the value of current flowing into (charging) or out of (discharging) the battery. Most modern cars if they have a meter on the charging system will have a voltmeter. A voltmeter gives much more information about the charging system.

For example, if a voltage regulator fails and charges the battery to 16+ volts, the ammeter won't detect this whereas a voltmeter will. But the voltmeter needs be connected very close to the battery so headlight current and operating currents won't cause a voltage drop like in the center console voltmeters in a 914.

I've updated the diagram for ammeter as well as a useful voltmeter like in Neil's diagram. This diagram is shown in a manner which gives some direction as to where the wires need to be run in the 914 tunnel.

The voltmeter or ammeter can be ignored if either one is not used.

If the ammeter is not used, then the wire from the alternator does not have to be moved.

Also added in is a 60A or greater fuse for short circuit protection from the battery. Modern cars have a fusible link to protect from shorts from the battery. This can be the type used in high power audio units. This is totally optional but given how much people tinker with their 914s, probably not a bad idea.

To install the ammeter, 2 wires need to be run in the tunnel to the ammeter. These can be probably be 10 gauge wires. The wire from the alternator is removed from the starter and rewired to the existing wires from the battery positive terminal. A tight connection to the existing wires is mandatory here since this is the source of all power to the vehicle when operating.

There may be several wires from the battery to electrics in the car including wire to the engine bay fuse panel. I'm flying blind here as I do not have a stock 914 handy to examine the wiring. Basically all the smaller wires (not the starter cable) need to be disconnected from the battery positive terminal and connected to the alternator wire. The only wire connected to the battery (besides the starter cable) is the ammeter cable and voltmeter wire if using one.

All these wires must have a very secure connection. The performance of the electrical system of your car depends on this. Poor connections and you will have problems.

For the voltmeter, just one thinner wire is run in the channel to the battery like 16 ga or 14 ga. The relay is mounted in the interior so it should be easy to wire up. The relay is needed else the voltmeter will be directly connected to the battery and will discharge the battery when the vehicle is turned off. The relay can be of a very small type that carries 1 amp or so.

i have to respond real quick (late for a car show). i just read the first part and will digest the rest shortly. i have s/w series 1 gauges... check. both volt and in 1 minute will place a bid on a s/w 30 amp. on e-bay... check

i'll get back this afternoon

thanks for the input

mike

Jerry's diagram nailed it - good luck with the install.

car show was great! one of the nices karman ghia's out there! a real cool burn out show, one 572c.i. elcamino was sumptin'

back to reality


i have a hand full of replacement fusable links, but i'm not sure of there amp. value. they are the "green" as i recall for a g.m. so i would imagine they are high amp. i also have a large inline 30 or 40 amp fuse. i understand the fusable link works slightly different, kind of like a slow blow. i'm thinking a 30 or 40 amp fuse would be good as i wouldn't think more than 30 amp's (charge or discharge) will ever go thru the 10 gauge wires. sound right?


check... i'll run 2 10 guage (ampmeter) 2 14ga. (1 for voltmeter and 1 to power trunk release future wire). it would be nice just to take power to the volt ga. from the hot side of ammeter (right next to each other)... do you think there can be that much voltage drop by tying in at the console end?


like a small fog light relay? i know there are "constant duty" soliniods for big draw/constant use... i guess the relay would hold up for a key on constant use?

here's the console gauge plate thats in the works right now. air/fuel is going to use the ammeter and the arangement will be different.

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