'78 power wagon questions

[fossilrider]

Hey Guys/gals, Steve (aka Fossil/Foss) here and new to the forum. I recently bought a one owner, low mile '78 Power Wagon and have a few issues I want to address before I put it on the road. First is the gas gauge doesn't work. The gauge in the left dash panel is a SW (Stewart-Warner) unit and I am wondering if this is the stock gauge or if someone has added it as a replacement for a stock unit? My experience has been that changing to an aftermarket gas/fuel gauge can give faulty readings since it and the sending unit weren't made to go together. At this point, I have no idea where the issue is, gauge, wiring, or sending unit so I still have some work to do. Another issue is the wipers don't work. I have power to the gang plug that plugs onto the motor but I read that these motors are known to be a weak point on these trucks. Also, I read that the ground is known to be a likely problem. Anyway, any help or suggestions would be greatly appreciated, since these two items are something that are handy to have in working order. Thanks, Steve

 

[multimopes]

Welcome aboard. I don't think the factory used any aftermarket gauges; even a well known name like Stewart Warner. I would clean all visible grounds first. Then I would be looking for voltage at each item that is malfunctioning. Good luck! There are many people here who really know their stuff, unfortunately I ain't one of em! That's why I am here also, lol!

 

[99Ram]

Welcome

 

[7mopar]

Disconnect the wire at the sending unit and put a test light to ground in the circuit. You only want too temporally turn the ignition switch on, so the gauge doesn't get damaged. The gauge maybe empty and show full or full and show empty. But you will at least know the gauge works. Wiper motor like to lockup on these if not used once in a while. I would take the electric motor apart and clean and lube it before going any farther.

 

[fossilrider]

Thanks for the replies guys. I wiggled the connector gang plug on the wiper motor and the motor rotated. It did it sporadically so I removed it and put power straight to the low and high speed posts and it worked fine.? So, I assume this is a connection issue. So, since it is a bit of a hassle removing it, I have ordered a reman motor and will clean all connections and add an additional ground when I install it. Also, while in there I have new pivot bushings to install, which should fix the wiper issue. Now I will have to move on to the gas gauge. I agree that the SW gauge is probably not a stock unit. It sits at just over 1/2 full when the power is off and moves to just under 3/4 when the switch is turned on. I ran out of gas just before I got home when I drove it 60 miles after buying it. I then put about 5 gallons in it to get the other 1.5 miles home so I know it doesn't have over 1/2 tank of gas . I dread pulling the tank, but saw a post where a guy simply took boards out of the bed to reveal the sending unit, which I think I will do. As for the correct gauge, I will have to do some research. Thanks again. Foss

 

[fossilrider]

Well, back on the Power Wagon ( got side tracked). Here's where I'm at now. After the last post, I installed a new wiper motor (rebuilt actually) and it works like a champ..... on HIGH, but nothing on low. With the age of this truck, as long as the parts I think are giving trouble aren't too expensive, I figure I will just replace them and I won't have to worry about that down the road. So, I thought it must be the wiper switch. Ordered a NOS switch and installed it today. Same problem, no low speed wipers!!!! So I dug out the manual and started figuring out the wiring (which is a big weak area for me). Everything seems OK, but there are two wires that plug into nothing at the wiper motor connection.? The diagram even shows the wires ending just short of the wiper motor. Very strange.? The wires have female terminals to slip over a male spade but there is nowhere to put them. Any ideas? Also, the issue with the gas gauge is still unresolved. I have a new sending unit and am trying to decide whether I want to drop the tank (which is about 8 feet long and would probably be a bear to drop), or just remove the bed to get to it. If I pull the bed, I might go ahead and have everything back of the cab blasted and paint it since there is a lot of surface rust on about everything there. I have decided to ditch the SW gas gauge and have a programmable gauge ordered. After I bought a NOS gauge, I found that the recessed area where the stock gauges go has been butchered in order to install the non-stock gauges. Why do people do crap like that? Anyway, Please let me know your thoughts that might help. As always, thanks in advance. Foss

 

[Brutiss300]

Sounds like an in-tank sending unit problem. W ethanol gas and corresponding sludge buildup...this is common in veh's that don't get full tanks and driven often!

 

[NioMarvin83]

Hi Steve, welcome to the forum!

For the gas gauge issue:

The SW (Stewart-Warner) gauge could be an aftermarket replacement. Dodge trucks from that time typically had Motorola or VDO gauges. If someone swapped the original, it could cause problems with readings, especially if the sending unit and gauge aren’t matched.
To check, try looking up the part number on the back of the gauge or comparing it to original specs online.
For troubleshooting, you can start by checking the wiring from the gauge to the sending unit and see if there’s any loose or corroded connection. You can also test the sending unit with a multimeter to make sure it’s working.
For the wipers:

Since you have power to the motor plug, it’s a good sign the switch and wiring are okay.
Wiper motors on these trucks can fail, but first, check the ground connection. A bad ground can cause all sorts of electrical issues, including no wiper function.
If the ground looks good, test the motor by applying power directly to it. If it doesn’t work, the motor might need to be replaced.
Hope this helps! Let me know if you need more info.