My Ammeter Issue

dpcd67 · Post by **dpcd67** » Mon Jul 16, 2018 7:55 am

Hooked up my M38 electric system after making the wiring harness from an M35 one. (That takes patience). Everything seemed to work fine until I picked up the gauge panel that was laying on the cowl, and it sparked when I picked up. Not good. I began testing all the connections and I found that the Ammeter housing was 24.7 volts and so was the gauge panel. Disconnecting wires 8 and 9 fixed it. Engine not running.
Now, for you guys who have later vehicles, Ammeters are a recipe for disaster. If they get frozen up inside they will burn your vehicle up. And they do not provide much useful information anyway.
So, I am going to put a red, yellow and green Volt meter in it. I like them; OK, not original. Dock me 5 points.

Post by **wesk** » Mon Jul 16, 2018 9:04 am

I am trying to find a technical question in your post???? I see that you successfully analyzed your problem and you have chosen a good alternative.

This may just be a technical education piece but then it lacks the complete solution.

So lacking any other positive indicator of what your tech question may be I'll make a guess and say: "What do I do with wires # 8 & 9 and where do I pick up power for the new voltmeter?" Or I can use this answer to complete the tech training statement!!

8 & 9 are capped (dead ended). The voltmeter then picks it's power up from the #27 spider harness. This way the voltmeter only draws current when the master switch is on. Most folks just switch their 4 wire #27 spider harness for a M35 series 5 wire Spider Harness.

mdainsd · Post by **mdainsd** » Mon Jul 16, 2018 10:44 am

Yes, the ammeter in these vehicles is a recipe for disaster (electrical fire).

Both leads #8 and #9 are effectively connected to the vehicle batteries all the time. Any issue with insulation of these small #14 wires and the results can be BAD.

Myself, I prefer the originality of the ammeter, but have to lose some originality to make them safe. First, they are really voltmeters that are reading the small voltage drop across the shunt (A piece of solid core wire) in the mechanical style voltage regulators. I have interrupted both wires very close to the regulator and added an inline fuse to each. In reality one fuse "would work" but there is a risk to burning out the ammeter in the instance of the wires shorting to ground. Fuse rating is very low, 1A. This fuse modification could probably be done inside the regulator itself, but I didn't do it that way. The way I did it I can change out a stock regulator for another stock one and all works.

Post by **wesk** » Mon Jul 16, 2018 11:26 am

but there is a risk to burning out the voltmeter

I'll assume since you already posted the analogy of the "ammeter is really a voltmeter" that you still are still referring to the ammeter and not Dpcd67's new voltmeter?

Since technical skill levels vary across the board on our web site I try to keep it as plain and simple as possible to avoid less experienced folks having serious issues with their jeeps because they misunderstood something more experienced folks take for granted is always understood.

mdainsd · Post by **mdainsd** » Mon Jul 16, 2018 11:47 am

Your assumption is correct. And point taken. I deal with this stuff day in and day out and have so for close to 45 years now.

I'll edit that so as not to let someone mess up looking at this thread a couple years from now!

dpcd67 · Post by **dpcd67** » Mon Jul 16, 2018 4:38 pm

I did not ask a question. I briefly outlined my solution to a problem. I did not
list every step. If someone wants the step by step on how to do it, or make an M38 wiring harness from an M35 one, I will be glad to walk them through it. Yes, you need a switched 24 volt source; and the #8 and 9 wires are no longer used and should be capped off, if you install a volt meter.