The Stovebolt Site Forums The Shop Area The Electrical Bay '58 Temp Gauge

I am still trying to finish the wiring on my truck (doing it in my spare time isn't getting it done very fast ). I thought that I had everything taken care of under the dash and in the engine bay when I went to hook up all of the wires to the gauges and the ignition switch. The wiring diagram I got on-line and the one in the shop manual both show the hot wire for the temp gauge coming off one of the ACC (Accessory) tabs on the ignition switch. However, when I hooked up the lead from the ignition switch to the ammeter, reattached the cables to the battery, and turned the key, the power lead to the temp gauge fried. I checked the temp sending unit on the engine block, and it is grounded. If I leave the temp gauge unconnected, the ammeter appears to work fine. The lights, turn signal, gas gauge, and dome lamp are all working. The temp gauge is a new solid state gauge to replace the old one that was no longer accurate and was somewhat falling apart. I cannot see any connection between the ammeter and the temp gauge other than through the ignition switch-is that a possible problem?-and that they are next to each other in the gauge cluster. Any help? Ideas? By the way, wiring to the temp gauge is 16 ga now versus the original 20 ga wiring.

You must be hooking the wire to a ground term. on the gauge or you have a defective gauge.

There are two terminals on the gauge, one goes to the temp sender on the block (which is grounded) and the other goes to a power source. I tried reversing them from what is shown in the shop manual, but got the same result. The Shop Manual did show the gas gauge backwards, but I didn't fry any wiring, the gauge just pegged out on E. I flipped the wires and it was fine. I'm thinking about trying to repair the old gauge and put it in to see what happens. Keep the ideas cominng. I hope to have the truck back on the road by Monday, June 4.

the sender is NOT ground, it is a resistance, which changes with temperature - if you have a good ohm meter you should find that cold it will register about 30-50 ohms, if it shows 0 ohms, a direct short to ground, 100% of the juice from the ign sw terminal will flow thru that wire, which is why it fries and the only thing that would do it ..... get a new sender

Bill

It seems to me if the sender was shorted it would just read hot all the time or cold on some units. There has to be a short at the gauge to fry that wire.

Lumbergh,

Bill is correct, the sending unit is a variable ground. The catch is that it isn't expected to pass much current. A #16 wire is good for about 8 amps. If you are actually burning this wire up it tells you that it is drawing 8 amps plus. This would be a huge amount of current for a temperature gauge. My bet is that the solid state gauge is cooked and taking any power attached to it straight to ground...this means all the current the wire can carry, until if melts in two.

Another possibility would be the solid state gauge has shorted internally and is passing power 'through it' and to ground at the sending unit. The wire from gauge to sender should show some signs of overheating if this is true. A simple test would be to disconnect the gauge to sender wire and see if something changes.

If you are going to dink with this thing, stick a inline fuse in the power to the gauge and save replacing wires as you experiment. Most solid state devices fail 'open'...they just quit working.

EDIT. As this is a special type gauge, did the manufacturer provide any special instructions for installation like a resistor inline on the power side.

Stuart

Check the terms. on the back of the gauge. There is a plastic insulator where it passes through the housing. It may not be in the hole & causing the term. to short to the case. Also some of those gauges use the terms. for mounting. There is an insulator where the terms. go through the mounting bracket. It may be missing or in crooked shorting the term to the bracket.

Wrenchbender:

You are correct, there is nothing insulating the posts from the mounting plate on the back of the gauge cluster that they pass through. I looked at the original gauge and it had a piece of cardboard between the back of the gauge and the mounting plate, but still no visible insulation between the posts and the mounting plate where they pass through the holes. i don't understand what kept it from shorting out against the gauge cluster through the post to plate connection. I'll try some rubber grommets, or whatever I can find that might work, tonight.

Red58 & Automarc:

I wasn't clear in my prior post. The side of the temp sending unit is grounded, as it should be according to the Shop Manual-there is good contact between the sending unit and the engine block. I will check for a resistance between the center post of the sending unit and ground tonight.

Thanks to all.

Lord knows I tried to warn the next guy so that he didn't have to live what I lived!

Bill

TxLaTx:

What keeps the posts from shorting out through the side of the posts resting against the inside of the holes that they pass through? It seems that the insulating cardboard just prevents a good connection between the post nuts and the gauge cluster backing.

Thanks for the attempted warning; sorry I didn't check for this before I went to make this simple installation. I guess that during the months between removal of the old gauge and installation of the new one I forgot about the cardboard insulator on the outside of the back of the gauge cluster. I could have sworn that there was nothing on the outside and the cardboard insulator on the one originally in the truck was on the inside of the back between the housing with the two wire coils and the back of the gauge cluster.

What irks me is that the little cardboard insulation cost is darn near FREE, yet it isn't provided with the $55 gage. I guess it helps to improve sales to "Don Knotts" electricians like me!

I can't remember how the gage cluster back housing doesn't short across the post nuts. I think I stopped learning once I got the gage working. My lessons tend to be rather costly...

*sigh*

I think all we can do now is wait for the next guy to post a question about a similar experience, and then we can sound like the gurus having lived it before!

Bill

I have a question..And I hope I am following you guys correctly. I I put all new Guages in my Dash..never checked for the insulator?? Cardboard..Or what ever you guys are describing.I have been having problems with my new Guages,kinda what you are describing . Got Mine from Classic..I guess what I am asking could I have the same problem as what you guys are talking about.

Mike, with mine, it stopped working and started frying the instant that power was applied. It took a millisecond for it to be ruined. I doubt you'd seen any intermittent problem if you were missing the insulation across the temp gage. It would either work, or not.

If you are having an intermittent problem, I suggest looking at the continuity at the temp sending unit at the block and the wire connections both at the sending unit and at the gage. If that was good, then you might consider looking at the power wire's connection at the gage and whatever you have the other end connected to.

Bill

OK..I am still working with My gen right now..Kinda stalled on it cause My Ignition locked up and I am waiting for a replacement to be shipped..I might try to unlock it with a piece of wire today,got other stuff to do too. new clutch spring..put the fly wheel cover plate on ect...

Thanks for the help guys. The rubber grommets appeared to have done the trick. Hooked up new wiring to the temp gauge and turned the power on with no annoying puffs of smoke. Of course, it looks like the gauge is fried now.

Guys..I finally got my Gas Guage...sender unit to work. Rewired it...The sender wire was krimped under the gas tank from when I re-installed it. I had a feeling about that...but I did not follow up on it. Ran the tank down removed it...there it was...Krimped and shorted...