Guages
 

Now that my tach works, I've got to question it's accuracy. It says I'm idling at 1200, I don't think so. It says 3700 RPM at 55 MPH. Seems a little high. I have a 1 Ton, with 402, 4 speed (Granny Gear first), 30.5 inch tall tires, and a rear end with 14 bolts in it. Anybody know how to check tach accuracy, and if what it says is right, isn't that an EXTREMELY high gear ratio? Is that why I run hot above 65 MPH?

You guys are makin' me work on my truck too much. Tonight I installed the 2 in line 4 amp fuses with new holders, and , DAMN, the 'BATTERY' gauge now works. I suppose next you'll tell me to hook up the green wire to the temp sender and the temp guage will work.

Couple of things you can do. First figure out your gear ratio then you should be able to determine what rpm you SHOULD be doing. The other is to get a automotive multi-meter with a tach function and compare that to your in-dash tach.

actually on the contrary 3700 at 55 in a 1 ton seems awfully low of an rpm, your gear ratio wil be at least 4.10 if not 4.57 or 5.14, if its dually then its 5.14 most likely and rpm at 55 wil be more like 4400+
usually top speed in a 67-72 dually 1 ton is 45-50 depending on engine installed, so...

a multi-meter? where do I get one? Is it a simple parts store type item? Thanks!

I know this a dumb answer but....on the back of some tachs there is a switch....it has 4 cyl...6cyl...8cyl... if you had it on 6 cyl...it could give you those readings

Id check to see if V8 tach,but a one ton dually could have real low gears,and big blocks done like to cruise at high rpms for long periods of times,plug in a aftermarket tach its simple to do to see if reads same,ive never had a factory tach that read the same,shouldnt be idling at 1200 i like mine at 800 in park,600 at the stoplight.Heres a thought drop off your tach here on the way to Pamona and ill give you a nice vac gauge cluster for it.

Most parts stores would carry a meter with the tach function I would think. Sears has one.

Thanks, Mike. I'll go to Sears on my lunch hour.