Gas, volt, temp, and 4wd light, not working. Choke light always on.

[AyWoSch Motors]

So I recently got my 86 GMC running and driving again. After driving around a bit, i relized some of my gauges don't work.
Speedo is working fine, except for the fact that when i go backwards the needle goes backwards. No idea why. Oil pressure seems to be working fine, reads 40ish on cranking 60+ when running.

Now the issues, are with the others. The temp gauge has never worked, the volt guave used to, but is now at 0. And the gas gauge has never worked well, but it was consistently off. 1/4 tank on the gauge was empty and quarter over full on the gauge was full, but now it kinda bounces around, seems to be in a different place every time.i figure bad sending unit, but idk.
And while were digging into gauges, my 4wd light has never worked, and the choke light is always on.

My question is, how to fix these things.
Could be wiring, not sure everything under the hood was hooked up right after the engine swap (rod knocking 305 to L98 350 for those who don't know). Im clueless on how to fix it. All i know, is that the alternator is charging, the engine is getting hot (i have a temporary temp gauge under the hood), it has about 6 or 7 gallons of gas in it, but id really like to keep track of it all real time and accurately.
I have a bunch of extra gauges, and extra gauge backers, but i suspect thats not the issue.
Any ideas or insight would be appreciated, thanks.

 

[bucket]

Speedo goes backwards in reverse because it's a cable drive.

Your fuel gauge, if it still seems to work but just a little more inaccurate than before, I'd suspect a fuel sender that got a little crusty when the truck sat. If you disconnect the sender wire, the gauge should read full and if you ground the sender wire to the frame, it should read empty. If that checks out, your gauge is OK.

You can do the same test procedure for the temp gauge.

The voltage gauge is likely a dud, or there's an issue with the printed circuit on the back of the cluster.

The 4x4 light could be a number of things. Blown bulb, faulty switch in the t-case, or an issue with the harness. The harness goes up through the shifter area and lays on the floor, under the carpet.

The choke light is tied into an oil pressure switch. Are you still using both factory oil pressure senders/switch?

 

[AyWoSch Motors]

Speedo goes backwards in reverse because it's a cable drive.

Oh okay, Didn't seem normal. I figured it would have a slip so it wouldn't read backwards. I often go backwards alot, and sometimes quite quick, will that hurt it, or snap the needle?

Your fuel gauge, if it still seems to work but just a little more inaccurate than before, I'd suspect a fuel sender that got a little crusty when the truck sat. If you disconnect the sender wire, the gauge should read full and if you ground the sender wire to the frame, it should read empty. If that checks out, your gauge is OK.

Thats what i was thinking too. Guess ill have to find a new one. Unless they're fixable/cleanable.
Didnt know you could test them, thats cool. Ill do that. It sat from 2006 to 2018 when i started driving it, so that makes sense.

You can do the same test procedure for the temp gauge.

Where does the wire for the temp gauge plug in, and what does it look like? It might just be that the wire is melted or not pluged in. There's a few of those under the hood.

The voltage gauge is likely a dud, or there's an issue with the printed circuit on the back of the cluster.

Thats easy, i can change that out.

The 4x4 light could be a number of things. Blown bulb, faulty switch in the t-case, or an issue with the harness. The harness goes up through the shifter area and lays on the floor, under the carpet.

I dont think the bulb is blown, because i think it comes on for a sec when you turn the key, probabaly the switch or the wire. Ill check it out.

The choke light is tied into an oil pressure switch. Are you still using both factory oil pressure senders/switch?

I believe so, but entirely sure. Im pretty sure i took both the pressure sensors out of the old 305 and put them back, but im not sure they're both plugged in.
The light should come on until its warm and shut off, right?


Thats all alot of help, thank you. Should get me going in the right direction.

 

[bucket]

The temp gauge wire is a green one with a slotted spade connector, normally plugs into a sender on the driver's cylinder head.

I've never actually known the exact purpose of the choke light. But basically, it is lit when the ignition is on and there's not enough oil pressure to trip the switch that sends power to the choke heater. I remember years ago when I installed an electric choke Holley on my stock '84 C10, I used the original choke wire. For whatever reason, the choke light wouldn't go out and the choke didn't ever get 12 volts. Maybe the oil pressure switch happened to fail when I installed the carb? I don't know. I simply ran a dedicated 12v ignition source to the choke and unplugged the oil switch for the original choke wire.

 

[SirRobyn0]

The only thing I have to add that @ bucket didn't mention is there is a resistor on the back of the fuel gauge in the cluster. When those fail it can cause odd issues such as being off a 1/4 of a gauge all the time. So if test points to a gauge issue don't overlook that. As far as I know the only test for the resistor is to just replace it.

 

[AyWoSch Motors]

The temp gauge wire is a green one with a slotted spade connector, normally plugs into a sender on the driver's cylinder head.

I've never actually known the exact purpose of the choke light. But basically, it is lit when the ignition is on and there's not enough oil pressure to trip the switch that sends power to the choke heater. I remember years ago when I installed an electric choke Holley on my stock '84 C10, I used the original choke wire. For whatever reason, the choke light wouldn't go out and the choke didn't ever get 12 volts. Maybe the oil pressure switch happened to fail when I installed the carb? I don't know. I simply ran a dedicated 12v ignition source to the choke and unplugged the oil switch for the original choke wire.

Oh okay thanks.

I curectly have 12 volt key on power to the electric choke on my edlebrock. It seems to be working.

Sounds like the solution to choke light issue is just pull the bulb, haha.
Sounds like to much of a pain to figure out.

 

[AyWoSch Motors]

The only thing I have to add that @ bucket didn't mention is there is a resistor on the back of the fuel gauge in the cluster. When those fail it can cause odd issues such as being off a 1/4 of a gauge all the time. So if test points to a gauge issue don't overlook that. As far as I know the only test for the resistor is to just replace it.

Good to know, thanks

 

[bucket]

The only thing I have to add that @ bucket didn't mention is there is a resistor on the back of the fuel gauge in the cluster. When those fail it can cause odd issues such as being off a 1/4 of a gauge all the time. So if test points to a gauge issue don't overlook that. As far as I know the only test for the resistor is to just replace it.

I didn't know it could cause an inaccurate reading. Well, at least not any less accurate than when new, lol. But it can let the gauge needle swing around rapidly with tank slosh. When the resistor is good, it will limit the speed that the needle moves.

 

[SirRobyn0]

I didn't know it could cause an inaccurate reading. Well, at least not any less accurate than when new, lol. But it can let the gauge needle swing around rapidly with tank slosh. When the resistor is good, it will limit the speed that the needle moves.

Your completely right, it seems to me that they can cause a variety of symptoms. Basically I've seen what you are talking about plus reading about 1/4 less than is actually in the tank. Of course when you open up the dash to change the resistor everything gets moved around and the connections cleaned up so there is that...