dash cluster woes

[fastlane]

I've rewired my truck, headlights to taillights, and overall I'm quite satisfied with the job I did! I just recently fired up ol' crusty and took her for a spin the other day, started right up without having a tender on it for months!

The problem I'm having is the dash, I switched from a 3 hole to a tach dash, yes I wired it correctly! per AAW instructions. the tach dash I bought had a delaminated PCB with weak grounds for the water temp gauge, now I've got a new PCB and now I've got no current to the water ten gauge at all. the gauge is pegged all the way to hot. the truck is obviously not hot at all.

So heres what I've learned from my research, AAW does not fill holes 1 & 12. and Gmcpauls tip page shows wires for the alternator there, I changed to a 1-wire alt. will that work with the battery gauge? also what else should I check to get the water temp gauge to work? it is a new sender. I remember researching the right resistance when I changed it.

[hugger6933]

The last time I worked on my 68 [a couple of years ago I guess it was now] i put in a new Tac/vac dash and wired it right and got about the same thing. It has been so long I don't even remember what was wrong. One day. Jim

[tedfrk]

To me it sounds as if you have voltage to the temp gauge all the time. If you have the key turned to acc does the gauge go up right away? Could be the gauge, or the sender check the ohms and see if its in range. Just because its new doesn't mean it works.

[tedfrk]

this might help

[notsolo]

You probably know this,!!! AAW has a schematic for gauges and 1 for dash lights. I know because I used the wrong page.

[tedfrk]

[fastlane]

I've double checked and rechecked the positioning of the wires, I have them correct... I think at this stage in the game I really need an ohm meter! I've got a current probe that I hook up to a source of power and it lights up if there is some.

will a factory battery gauge work with a 1-wire alt? then there is the question of what wire goes in the 1 and 12 position since I have eliminated the external voltage regulator and there is no junction block near the battery.

oh and the water temp gauge is always pegged "hot" and only moves slightly to the hotter position, temp readings at the therm housing shows 160-175

Once upon a time I have an ohm meter from harbor freight, had to return it 'cause it wouldn't even measure 1.5V of a AA battery...

[Big Kev-O]

In the origional circuit for the battery gauge terminal #12 connected the fender terminal block near the battery and terminal #1 connected to the three way connector of the alternator, regulator,and the battery. Both wires will be 12v + and should have 4amp fuses. I don't believe the wires you need came with your new harness.

[tedfrk]

the voltage gauge will work just need a + preferably from the fuse block and a ground. I think you have a bad ground some where.

[tedfrk]

Get some pics .

[ray_mcavoy]

Originally Posted by fastlane

I've double checked and rechecked the positioning of the wires, I have them correct... I think at this stage in the game I really need an ohm meter! I've got a current probe that I hook up to a source of power and it lights up if there is some.

An ohmmeter would be helpful for troubleshooting the temperature gauge. But you can still do a fair amount of testing without one. For example, you can disconnect the sending unit wire and note the reaction of the temp gauge ... it should swing to the cold side of the scale with the sending unit disconnected. Similarly, temporarily grounding the sending unit wire should make the gauge peg to the hot side.

Since your gauge is pegging hot, it sounds like your sending unit or it's wire might be shorted to ground. Check to make sure the wire didn't get pinched anywhere or melted on the exhaust.

Originally Posted by fastlane

will a factory battery gauge work with a 1-wire alt? then there is the question of what wire goes in the 1 and 12 position since I have eliminated the external voltage regulator and there is no junction block near the battery.

Yes, the factory battery gauge can be made to work with any alternator.

However, if you used an AAW Classic Update harness (as opposed to AAW Factory Fit harness), it won't have the charging system wiring configured to support the factory battery gauge (which is basically an external shunt ammeter).

You could re-configure the charging system wiring so it has the necessary shunt wire and add wires going to cavities #1 & 12 of the cluster connector to work with the factory ammeter. But an easier solution would be to simply convert to a voltmeter from a 76+ truck. Fellow member TBONE1964 is offering 76+ voltmeters that are already modified to fit 67-72 gauge clusters.

[VetteVet]

As usual Ray hits the home run.
If you are seeing hot on the gauge with the key on it is because the current through the gauge is running straight through the gauge resistor and to the ground and not going through the sender unit resistance. If you disconnect the wire from the sender and the gauge goes to cool then the sender is not functioning. If it remains on hot then the wire or the gauge is grounded. I know I'm being redundant, here but it is also possible for the gauge to be grounded itself. There should be two sleeves on the gauge terminals to insulate them from the dash cluster. If they are missing then the gauge will ground to the cluster and you'll get the hot reading. The sender wire in the picture goes to one and the red wire from the cluster board goes to the other. It will blow fuses if it is grounded.



Here is my favorite picture of the battery gauge wires and the shunt that is needed for the battery gauge to work. IF the one wire output wire is run to the opposite end of the shunt from the battery then it will work, or as Ray said "any of them will."



The shunt is labeled and in the stock factory harness it is used to charge the battery and the battery gauge wires are attached at the battery end and at the alternator end so that it can read the voltage potential between the battery and the alternator. IOW charge or discharge. This diagram shows why the battery gauge wires are both positive and not as so many guys think, one is positive and one is ground.

[cooperhw]

Bump so I can find my way back again.

My wiring

Think I might need some help.

[snipescastle2]

those gauges had insulators on the studs to prevent shorting the circuit board to metal mounting plate, if you had an Ohm meter, you could check for continuity and verify if this is the problem.....
HTH,
Ben

[fastlane]

well I picked up a multimeter, and the resistor on the temp gauge is at 83.6 ohms, and between the posts that attach to the PCB its 50 ohms. does that mean its shorted out? the temp sending unit is at 1.3ohms but thats cold (27-30* in the garage) I did realize there is teflon tape on the gauge, I will remove that asap, and see what happens.


I'm really not sure what to do with the battery gauge, and how to wire it! trouble shooting electronics makes my head hurt!

[ray_mcavoy]

Originally Posted by fastlane

well I picked up a multimeter, and the resistor on the temp gauge is at 83.6 ohms, and between the posts that attach to the PCB its 50 ohms. does that mean its shorted out?

No, those sound like fairly normal readings. If it were shorted out you'd be seeing a much lower reading ... zero or close to it.

However, you should also use your multimeter to check the resistance from the cluster case (ground) to each of the temp gauge's posts as VetteVet & Ben mentioned. Only the silver ground post should have a direct connection to the case ground.

Originally Posted by fastlane

the temp sending unit is at 1.3ohms but thats cold (27-30* in the garage) I did realize there is teflon tape on the gauge, I will remove that asap, and see what happens.

That 1.3Ω reading sounds like you have a defective sending unit. It should be approximately 520Ω at 100°F and only decrease in resistance as the temperature increases.
I don't think the teflon tape is causing your problem ... if anything, that would increase the resistance and make the gauge read too low.

Originally Posted by fastlane

I'm really not sure what to do with the battery gauge, and how to wire it! trouble shooting electronics makes my head hurt!

Well, you've got a decision to make on that one. You could either:

(A) Keep the existing battery gauge and wire it up exactly as shown in the diagram VetteVet posted earlier. Be aware that the routing and wire gauge of the battery charge wire is important since it also serves as the ammeter's shunt. And the two 4 amp inline fuses circled on the diagram are important too.

(B) Convert to a 1976-up voltmeter as I mentioned earlier. The voltmeter can simply be hooked up to the temperature gauge's existing power & ground connections.