Hello!

This is actually part of a project on my truck, but I'mnot getting an answer on TDS, so maybe someone here will know.

How is an aftermarket (i.e. a cheap-o Sunpro) ammeter supposed to be wired up?

I was at one point told that, ideally, all of the vehicle's electrical load should go through the ammeter. So, currently, I've got things wired so that the small lead from the battery (which would otherwise go to the starter relay, with another wire going to the glow plug relay) goes directly to the glow plug relay. A length of 4 gauge welding cable goes from the relay to one terminal of the ammeter, and a 6 gauge wire connects the other terminal of the ammeter to the "main" power terminal on the starter relay. This way, all current in the electrical system, except power going from the battery to the glow plugs and to the starter, goes through the ammeter. Things have been working well so far (over 2 years now), but I was told a while back that wiring the truck like this was potentially dangerous.

With my engine compartment torn apart, I've got a golden opportunity to make things right, so any comments on this would be greatly appreciated...thanks in advance!

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2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999

An ammeter is designed to be hooked up in series with the positive lead on your truck...in terms of doing diagnostics with a handheld device, I'm okay with this. But a permanent gauge?

That's a LOT of current to be passing through a cheapo (or expensive) unit. I see a lot of issues with this setup:

1. 4-gauge wiring behind the gauge? While adequate for that type of load, I wouldn't run that much current behind the dash unless you want to risk a fire! Consider that as you crank your vehicle, your starter demands several hundred amps!!!

2. Your fuse panel is the link between your in dash harness and the other components throughout your vehicle. Except for the 25-30 amp jobbies used for some of the more demanding components, your in-dash wiring is carrying 15 or so amps tops.

3. Since your ammeter is designed to run in series, you don't want to make it the "faucet" for the rest of your electrical system. If your ammeter fails, everything else is DOA. And since you admitted to it being a "cheapo" gauge, do you really want to bank your whole electrical system on the integrity of that unit?

The best you can hope for here is an "extrapolation" of the health of your electrical system.

My suggestion is to find a lead from the fuse panel that leads to a non-essential accessory (such as a cigarette lighter). It should be one that is only "hot" when the ignition is on. You can splice the wire going from the fuse to the accessor(ies) and attach each end of the ammeter terminals to each of the spliced leads.

The ground lead to the ammeter is only used for the gauge illumination...do NOT attach a vehicle ground wire to either of the ammeter's terminals, unless you want to see a quick demise of said ammeter.

Hope this gets you going the right path...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

A volt meter is a simple hook up and in fact tells you more about whats going on with your charging system.............

William Rogers........

Yup, and they're the main culprit for electrical fires in most older cars so equipped. Too dangerous for me. I would not have unfused full main current flowing through the firewall. Too much chance of a short.