Rebuilding 240z Gauges to Work with 280z Harness

[ModernS30]

I will take some pictures in a moment. I am using my full 280z wiring harness in my 240z. The 240z came with a harness but it was all hacked up. I am going to be putting the 280z dash harness in the dash as well. This is all a big huge pain in the you know where. The reason you have to do this is the 280z gauges use different wiring as well as mounting. Basically I wanted to help some of the people that might not know how to do this, as I didn't till I started messing just a little while ago. You have to remove the 280z and 240z gauges.

 

To start, remove all the wiring, DO NOT FORGET WHAT GOES WHERE! Then you need to remove the 2 gauges from the dash board. After you do this there are 4 screws holding the black plastic 'housing' onto the gauge. Remove the screws and then remove the 'housing'. You will be left with the little metal part of the gauge. There are 2 studs that the wiring hooked to on the back that are also bolted onto the metal housing. There is a white plastic part under these. Remove those, remember though this entire process to keep track off all of your hardware and what goes where. There are going to be 2 screws left on the gauge at this point. Remove those to. At this point you need to be very careful. Don't just pound on the gauge to get it out. You will be removing the entire assembly. There are 2 small screws you could remove that may make it easier. I didn't try this. You can use those screws to sort of press out the gauge, just be easy, they are going to be kinda stuck in there. You will get the entire assembly out and then you just reinstall the opposite.

 

The above process was with the tachometer. I haven't played with the speedometer but I am not looking forward to it. I will post pictures of all of this when I finish.

[Blitz21]

I'll definitely be watching this since I might have to go a similar way and I don't have the time to do a painless.

[xxxpatsabxxx]

should be stickied when pics come along....

[ModernS30]

Ok, here are a few pictures. I will do my best to explain and go back for an edit later on. I am tired, have work in the morning. Then race track after wards.

 

Here are the 280z gauge housings, I will get pictures of the 240z ones but they are already installed.

On these note the large 'arm' as a mounting tab. The one on the bottom is the speedometer, top is tachometer. The 240z housings have bolts on them that wing nuts attach to to hold the gauge in the dash board. There is only one major difference other that that I found about the housings. The 280z speedometer has some sort of relay. You will need to find a place to mount this. I used the actual gauge mount. On the 280z speedometer housing there are 3 holes (right side in picture, under mounting 'arm'). The middle hole has a single red wire going through it. The 240z housing does NOT have this hole. That was the only modification I had to do, you just need to drill a small hole. Doesn't affect the operation, just allows the wire to pass.

 

 

These are the 240z gauges out of the housings (Tachometer left, speedometer Right). The main eye to eye difference is that 280z speedometer has that earlier mentioned red wire attached. All the mounting in the housings is the same. The connectors on the 240z gauge and 280z gauge are very similar, you may be able to splice or make adapters. It seemed like this was easier.

 

 

Ok, this is the 240z speedometer laying in the 280z housing. The removal from either gauge is universal. You remove the two center screws where the speedometer cable attaches, the trip reset cable, and all the wiring (MAKE SURE YOU KEEP TRACK OF WHAT GOES WHERE!). Then the assembly will just pop out of the front. Install is just the opposite, the main thing you will need to do is drill the hole for the red wire on the 280z speedometer. Other than that reverse your install. You will have to mount the Relay from the 280z wiring and the ground. I just used the gauge mounting bolt. I had to bend the relay bracket and enlarge the hole. It wasn't very difficult.

 

 

Here is a picture of the hole I drilled with the little red wire I keep mentioning.

 

 

This the the 240z tachometer laying in the 280z housing. Again the Taking apart and putting back together is the same. This will require no drilling just a screw driver and a 5.5 mm socket, you shouldn't, but may, need a ratchet. Remove the few small nuts that hold down the plastic clips on the housing. After that just remove the 2 screws that sit diagonal from each other. The tachometer will be pushed out of the bottom. Be careful as I managed to crack the little brown board under the connectors. The 280z and 240z gauges are very similar but have a few minor differences in the connectors.

 

 

I hope this helps. I will try to do better later. If you have any questions feel free to ask. I will answer to the best of my ability. I am not sure if any of this was necessary but I felt it was so I went for it. It was not nearly as hard as I expected. Just little screws. No little gears in the speedometer and crap that I expected to fall out.

 

Kinser

Edited May 22, 2010 by ModernS30

[wal280z]

I am using my full 280z wiring harness in my 240z. The 240z came with a harness but it was all hacked up. I am going to be putting the 280z dash harness in the dash as well. This is all a big huge pain in the you know where. The reason you have to do this is the 280z gauges use different wiring as well as mounting.

 

Just curious - which year 280 harness / internals are you using? If I recall correctly, the 75 - 76 gauges have the same font style as the 240, the process you are going through might be a bit less painful if you use those years. Also, I recall the 75 had an amp gauge while the 76 had a volt gauge. With that said, I'm not saying that you could skip the changes to the mounting configuration.

[ModernS30]

Just curious - which year 280 harness / internals are you using? If I recall correctly, the 75 - 76 gauges have the same font style as the 240, the process you are going through might be a bit less painful if you use those years. Also, I recall the 75 had an amp gauge while the 76 had a volt gauge. With that said, I'm not saying that you could skip the changes to the mounting configuration.

 

That is a very good point. I should have included this information. The 240z stuff is from a 72, not sure of the build date. The 280z stuff is from a 4/77. I haven't gotten to the smaller gauges yet. The 280z does have a volt gauge. This will vary from model to model at least a little bit. Sorry I do not have every year to confirm, wish I did.