fule&temp gadges peg out when key is on

[moparmike]

truck runs fine charges the batery but the gas gadge will peg then the temp it is a 64 it has had electronic ignition and newer alt/and regulator added but it is an other wise unmolested wireing harness

any one got any ideas?

[Jeffc]

Unlike most cars the trucks have a voltage limiter (regulator) built into the
fuel gauge. When these start to go bad the limiter will start passing a
full 12v to the gauges. A full 12v to the gauges will cause the gauges
(fuel and temp) to peg, if for long enough it will cook the gauges.
Link below will give a look at this issue, also photos that follow.

http://imageevent.com/jeffc/techstuff2e ... =4&s=0&z=2

You may place a new limiter in-line to control voltage (car type) or build your own.

[moparmike]

today i went out and started it and the gauges worked fine can the voltage limiter thing be intermittent

[Jeffc]

Yes it can. Best bet to save your gauges is place a new limiter in line,
it may be placed were the power feeds the fuel gauge or at the top
post that feeds power to the temp guage (back feeding the fuel gauge).

[OrangeRoughy]

Hello All, my first post. I've read through a lot of the site and believe I've come to the right place for questions on my '64 Powerwagon 200.

Like the thread, my fuel & temp gauge peg when ignition is activated. I looked through the attachments Jeffc provided on making my own resistor as it appears my fuel gauge resistor is probably fried. My question: if I just wanted to take the easier approach of employing a NAPA resistor off of the red wire to the fuel gauge what one should I ask for?? Also, am I correct to assume I would need to do create a "Y" off the new resistor to connect one end to the fuel gauge and the other to temp gauge?

Thanks for the help!

[Russ]

Putting a resister in line is probably not a good idea. The guages need a constant voltage to work right. The temp and fuel sending units are variable resisters themselves so as the temp and fuel sending units changed resistence you would have a variable current through the resister that you added which would make your voltage drop across it vary. I don't think your guages would be very accurate. It's cheap to buy a regulator or make it your self so that's the way I would suggest that you go.

[OrangeRoughy]

Thanks Russ,

My error in regulator vs. resistor. What regulator would you suggest (I'd rather not build one)? In addition, if I place the regulator in line, will the "Y" scenario I indicated work or would I need to wire it differently? My thought was I could not just wire regulator to fuel gauge (knowing fuel gauge provides flow to temp) because the flow would be interrupted by the old, non functioning gauge-based regulator...correct.

Your thoughts appreciated.

[Sterno]

If the truck gauges are regulated down to 5 volts like the passenger cars of that era, a "7805" voltage regulator should do the trick.
Mopar Action had an article on rebuilding the regulator with the 7805. i'll try to find it in the stack of back-issues.

[OrangeRoughy]

Thanks. I'm assuming I'm correct on my "Y" wiring assumption as you guys have not "waved me off" on that one. Appreciate the help!

[Hobcobble]

Thanks. I'm assuming I'm correct on my "Y" wiring assumption as you guys have not "waved me off" on that one. Appreciate the help!

I'm no help on the "Y" question but I'd wait until there is an "official" "waive off" from someone
who is sure. Jeff Clare [aka Jeffc] might help you out if you e-mail him in case
nobody else assists.
John
PS.... Welcome to the site

[Sterno]

Thanks. I'm assuming I'm correct on my "Y" wiring assumption as you guys have not "waved me off" on that one. Appreciate the help!

I'm still not sure what voltage we need to regulate down to, if someone could hang a voltmeter off the regulated output on their truck, i'd appreciate it.
I'm going to assume that it's 5 volts like the passenger cars of the era.

What you'll want to do is pretty simple really.

First, you'll have to disconnect the buss bar from the fuel gauge, we don't want it getting any power from anywhere but the regulator. Then mount the regulator on the back of the instrument cluster with a screw and a heatsink for it (readily available at radio shack etc.). Then connect terminal 1 to switched 12 volts, terminal 2 to a good ground, and terminal 3 to the regulated output stud on the fuel gauge(f-12). Leave the wire from the fuel gauge to the temperature gauge in place, it will feed the temperature gauge.

If we need to regulate to a different voltage we replace the 7805 with a 7807 for 7 volts, a 7809 for 9 volts.....etcetera.

Best of luck

[Russ]

The factory Sweptline regulator is very crude. It actually doesn't regulate, it just opens and closes a set of points. If you try to meter the regulator output you will see that it swings from about 5 volts to about 7 volts. I don't think the guages changed when the manufacturers changed to 12 volts from 6 so that is why they regulate it down to about 6 volts. I think the mid 60s Mopar cars had an external regulator that mounted behind the dash. I've seen them advertised in Mopar Collectors Guide. Try the Year One website and search through their catalog, I think you will find a picture of it.

[OrangeRoughy]

Thanks Russ & sterno,

With the descriptions you've provided I'm ready to tackle this. Feel dumb asking but what do you mean by "buss bar"??

Thanks again, and I'll see if Radio shack has a 7805.

[Sterno]

the buss bar is the piece of brass that runs between the studs on the ammeter and the fuel gauge. you'll understand as soon as you pull your gauge panel and look at the back of it.

good luck with the conversion

[surfnuke9]

If you just want to buy a new, solid state regulator, Redline offers them.

Here is one on EBay... http://cgi.ebay.com/ebaymotors/ws/eBayI ... MEWAX%3AIT

[Sterno]

If you just want to buy a new, solid state regulator, Redline offers them.

Here is one on EBay... http://cgi.ebay.com/ebaymotors/ws/eBayI ... MEWAX%3AIT

that IS the easy way. I'm a cheapskate though and the 7905 and heatsink together shouldn't cost more than seven or eight bucks.

*edit*: of course the regulator can will have to be butchered onto our gauge panels much like the 7905 setup, due to our oh so convenient "regulator in gauge" deal.

[OrangeRoughy]

Well guys, finally had some time this weekend to attack the regulator/gauge issue. Thanks to the info here, I spliced inline a 7805 regulator form Radio Shack but ended up with NO readings on gauges (except AMP) and I also lost my turn signals When I removed regulator, I got my turn signals back.

I tried different grounds, key in "on" as well as truck running, no difference. My test light showed weak current through the regulator to the gauge (which I would expect at only 5v). In re-reading my print out from here, I realized I neglected to disconnect Buss bar, but I don't think that is the issue as it would be getting more juice, not less.

Any suggestions???


Thanks!

[JimKoz]

The regulator from the Mopar Action article ("Gage Rage", August 2000) is National Semiconductor's LM7805. There is also the LM317 which is adjustable if you'd like to fine-tune the output voltage. The original article from Mopar Action is here:

http://www.imperialclub.com/Articles/Ga ... /index.htm

If you're interested in using the LM317, this reference might be helpful:

http://www.geocities.com/pdq340/regulator/index.htm

[Sterno]

Well guys, finally had some time this weekend to attack the regulator/gauge issue. Thanks to the info here, I spliced inline a 7805 regulator form Radio Shack but ended up with NO readings on gauges (except AMP) and I also lost my turn signals When I removed regulator, I got my turn signals back.

I tried different grounds, key in "on" as well as truck running, no difference. My test light showed weak current through the regulator to the gauge (which I would expect at only 5v). In re-reading my print out from here, I realized I neglected to disconnect Buss bar, but I don't think that is the issue as it would be getting more juice, not less.

I've got a nagging feeling that the 7805 regulator got toasted by having 12 volts connected to the output via the buss bar. the only way to check this is with a voltmeter, disconnect the output from the gauge cluster and read the voltage. Re-Read my posting and noticed that I left out the capacitor, but that shouldn't cause you problems, it's there to smooth out voltage ripple from the output of the 7805

The 7805 and the lm317 are both rated for 1 amp of current, plenty to run our gauges. National Semiconductor is one of the major manufacturers but any brand 7805 will be rated the same.

The turn signal problem strikes me as really odd. where did you connect the 7805's input side to power?


BTW thanks JimKoz for the link, i hope e-berg don't find out

[JimKoz]

BTW thanks JimKoz for the link, i hope e-berg don't find out

I think he'll be cool with it...especially since he posted a better version of that article on Allpar's website:

http://www.allpar.com/history/mopar/electrical2.html

National Semiconductor is one of the major manufacturers but any brand 7805 will be rated the same.

Yes, but I work for National, hence the shameless plug. I just found that we've discontinued the LM7805 and are recommending the LM340 as its replacement.