When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey guys, I'm sure some of you have been following my progress on the Autometer dash cluster project I've been doing.
Tonight I finally got the GPS hooked up for the speedo and both the sending units for the oil pressure and water temp.
After firing the truck up all the gauges are operating as they should.
However the problem exists with the low battery / low charge light and the engine light. Both are staying on.
The charge light will come on as soon as you move key to the accessory position and stays on after the truck is started.
The engine light only comes on the moment the truck is started but does not come on in the accessory position.
The engine light is ran to the Pink/Grey wire 658 Check Engine Input from EEC (Pin #9 from C251)
The charge light is ran to the Red/Light Green wire 904 Amp indicator Output (Pin #13 from C251) This is also the same wire that needs the switched 12v in order for the Alt to charge. Probably why the light is staying on due to the switched 12v?
Did you install a resistor in parallel with the charge light? It's installed on the original cluster. Don't have much info on it, but I read that the circuit with that lamp is used to sense battery voltage, so they put a resistor in parallel so that the circuit will not be open when the light blows.
On my truck (1994) it's a 500 ohm resistor. By my calculation it should be greater than .39 watts, so 1/2 watt minimum. Don't know what kind of light you have, but it could be interfering with your charging circuit, especially if that resistor isn't in there.
Did you install a resistor in parallel with the charge light? It's installed on the original cluster. Don't have much info on it, but I read that the circuit with that lamp is used to sense battery voltage, so they put a resistor in parallel so that the circuit will not be open when the light blows.
On my truck (1994) it's a 500 ohm resistor. By my calculation it should be greater than .39 watts, so 1/2 watt minimum. Don't know what kind of light you have, but it could be interfering with your charging circuit, especially if that resistor isn't in there.
Hey thx for chiming in. I believe you are correct. I didn't add the resistors. Looks like I'll be purchasing some to get this wrapped up. After I finish my coffee I'll head and grab a meter to see where the charge system is at while running vs. not running.
I am confused on how to determine what ohm and watt resistors I need.
Last edited by Inside Man; 01-13-2019 at 09:44 AM.
Or remove the resistor from it, &/or the one on the cluster film circuit, and re-use them?
Hey Steve thanks for jumping in.
Yes that would be the most sensible thing to do here but with the way the cluster was set up, at this point I feel like there's no turning back because I can't find the same design light with a regular bulb without having to change them all and I don't want one of them on the cluster being different from the rest aesthetically speaking.
Just to verify there is in fact an exciter issue here. I tested the battery with a multi-meter.
Engine off is 12.24
Key in accessory is 12.0
Engine running is 11.78
Now, I've had a 3G Alt sitting on the shelf to swap in after the current alt meets its maker. If I'm not mistaken, if I swap the 3G in I shouldn't need to do a resistor because the 3G has an internal exciter. Is this correct?
Factory Cluster Factory Cluster
Id rather not part out the factory cluster being that it's in great condition and would like to sell it.
Last edited by Inside Man; 01-13-2019 at 12:43 PM.
The drawing you provide shows the 510 ohm resistor, and Steve's link shows a 510 ohm resistor. You can reuse the resistor that was used previously, or you can get fancy.
I went to Mouser.com and saw they had some chassis mount resistors that can definitely handle the power and (to me) look pretty cool. It's a bit over the top, but it's relatively cheap (<$5 before shipping).
The big consideration in the resistor is heat dissipation. If the resistor has too much current going through it, it will heat up and open. It may also char any surrounding components. Therefore wattage is important.
The way to determine the wattage is to use the formula P = E^2/R where P is the power in watts, E^2 is the square of the max voltage you anticipate, and R is the resistance. I figured the max voltage differential you'd see is around 14.4V and plugged that value in.
The drawing you provide shows the 510 ohm resistor, and Steve's link shows a 510 ohm resistor. You can reuse the resistor that was used previously, or you can get fancy.
I went to Mouser.com and saw they had some chassis mount resistors that can definitely handle the power and (to me) look pretty cool. It's a bit over the top, but it's relatively cheap (<$5 before shipping).
The big consideration in the resistor is heat dissipation. If the resistor has too much current going through it, it will heat up and open. It may also char any surrounding components. Therefore wattage is important.
The way to determine the wattage is to use the formula P = E^2/R where P is the power in watts, E^2 is the square of the max voltage you anticipate, and R is the resistance. I figured the max voltage differential you'd see is around 14.4V and plugged that value in.
Ummmmmm......... What
Math has never been one of my strengths........... Or at all a strength. Lol!
So my guess is I could eliminate all this just by swapping to the 3G Alt with the built in exciter...... Thoughts?
I have it sitting on the shelf in the garage so it's not like it's going to cost me anything.
My philosophy after so many years of machine repair is: fix what you know is wrong.
In this case, the alternator does not work after putting in your new cluster. I would put a 510 ohm 1/2 watt resistor in parallel with the light and see what happens.
Alternatively, you can try the different alternator (no pun intended, strangely enough). Not sure your light will work then.
Keep us appraised of what you decide and how it turns out. I'm curious to know.
Gotta run, get to work overtime today.
No. The 3G works exactly like the 2G; it needs a 12V signal on the "I" circuit to turn on.
Originally Posted by Inside Man
Id rather not part out the factory cluster...
Then just find a resistor exactly like the one on the film circuit for the ALT indicator. The resistance is given in the diagram YOU posted; the wattage is indicated by the physical size of the resistor, but 1/4 Watt should work in any case.
01-12-2019, 10:47 AM
Could use some help with aftermarket gauge wiring
