Instruments

[ldmack3]

I am slowly removing items from the cab and painting. I decided to pull the instrument panel and not only paint panel and bezels replace some of the internal lighting in gauges that are out and if possible replace the red with white bulbs. Got the panel out and the tach and speedo have no lighting. The others seem to be sealed and I'm wondering if there is a way to open them up to replace the bulbs. So far I've been extremely careful and can't open any of them although removing all the nuts on the studs does allow the meter movement and dial to move around, but not take it out. Are these repairable?

 

[runk]

A thread about opening and cleaning the gauges-

Gauge repair question

Hey anyone can the gauges on an M35 be taken apart and cleaned without damage ? Thanks Jerry

www.steelsoldiers.com

But ! There are no lights in the gauges themselves, they get illumination from the bulbs on the panel. That is one reason the bulbs are mostly covered on the front side. Cleaning the bulbs and holders, and the circumference of the outside of the gauges where the light passes into them can make a big difference.

 

[ldmack3]

If there are no lights inside them why is there a common wire run to each one with the exception of the speed and tach? Even the non electrical have this wire. A ground maybe? I did find the windows horribly dirty and with overspray. If that is correct, no internal lighting, that will be a blessing even at $50 - $65 a pop for the small ones.

 

[SCSG-G4]

Military used red so it would not show as a white light (night time target).

 

[NDT]

Runk is right, the gauges do not have bulbs inside, they are lit indirectly by the lights in the panel. Don't open the gauges. The wires going to the gauges are +24 volt power on one and the other goes to the sending unit.

 

[ldmack3]

Just ordered 4 of the small gages. The fuel qty was new and I don't want to replace the tach and speedo. Much simplier. So the one wire is 24V? They were all bussed together on the back of the tach. Have to make sure I get them connected correctly isolated from ground.

Thank for the education everyone!

 

[NDT]

" correctly isolated from ground. "

No no no the gauge housing needs to be grounded in order for the gauge to work.

 

[ldmack3]

No I mean the wire with 24 volts isolated from ground. The panel has an additional wire going to ground.

 

[Floridianson]

Been awhile but I do not remember a ground wire to the panel. Thought it got its ground when we tighten the screws on the panel to the dash. Thought there was someone that said if gages start acting wonkey for no reason loosen all four screwy things and tighten them back down and or tighten up the gage horse shoe retainer nuts so it bites into the panel.

 

[ldmack3]

Yea maybe previous owner had that problem and added the ground. I like having a positive ground.
Any recommendations while the panel is out? I'm considering replacing the air hose and possibly the speedo cable. Need to take a closer look at the cable but the hose is old and cracking. Wiring is 50 years old so pretty rough but still functional. I'm hooking the defrost up to the heater while I've got the panel and glove box out for paint.

 

[Recovry4x4]

I forgot too but isn't the spider wire the hot wire.

 

[ldmack3]

This is a separate wire from one of the instrument clamp nuts to ground. I though the spider wires were lighting but apparently they are 24v.

 

[Recovry4x4]

All gauges that are electric, ground through their sending units. All 3 lights ground through the dash panel and the spider wire provides 24V to everything. Someone may have added a ground wire if the gauge panel wasn't grounding through the paint or whatever.
Resource was TM9-2320-361-20 Appendix E.

 

[ldmack3]

Thanks for the reference. It's definitely an added ground.

 

[Floridianson]

All gauges that are electric, ground through their sending units. All 3 lights ground through the dash panel and the spider wire provides 24V to everything. Someone may have added a ground wire if the gauge panel wasn't grounding through the paint or whatever.
Resource was TM9-2320-361-20 Appendix E.

I thought the ground was through the panel to the cab. Would not if the ground was through the sending unit would that not make the the gaged peg out and not read correct.

 

[ldmack3]

According to that appendix the sending units provide a variable ground to the gauge based on their reading of the press, temp, etc. Looks like panel ground would be for the lights, but this is my first crack at this so I'm learning as I go. I've done a lot of electrical and avionic work on jet aircraft but this is a whole different beast!

 

[Floridianson]

Yea I am here in body not mind so think your right. Good thing I am old, grumpy and can not think worth a crap even when I am here in mind.

 

[ldmack3]

I can ID with that.....

 

[ldmack3]

Ok got the speedo and tach painted, all other indicators on order. Painted panel. Inspected the "spider" wiring harness...not good. Several repairs with black tape, lots of cracks. Shows PN 8376501. Checked Ebay, Amazon and Tried all the Memphis, Eastern, Boyce, TNJ, etc. 19 additional suppliers. Found ONE for a Power Wagon, same PN but different connectors. Before I try to build my own I'm looking for suggestions.

I found one under 8376502. As if I'm not already confused enough the seller states " This is a common ground harness for all Military Truck gauges."
I'm going for it.

 

[runk]

Here is one -

5-Wire Instrument Cluster Wire Harness, 8376502

5-wire gauge power harness. Fits 2.5 and 5 ton trucks in the M35A2, A3 series, and M39A2 series / M54A2 using rubber shell connectors on gauges. <br> P/N 8376502. NSN 6150002205105. Made in USA. New/unused. 0.2 lb

www.eriksmilitarysurplus.com

Eriks keeps pretty good stock of the electrical stuff and reasonable prices.