In my 51 GMC, 261 inline 6... I'm trying to start the motor for the 1st time after it being rebuilt. I noticed when I hit the starter button the temp gauge jumped to about the middle. I touched the copper line that goes into the block and it was hot. Real hot. It cooled down pretty fast. I thought the copper line must have touched the back of the ammeter under the dash or something but it wasn't touching anything. The only thing I can think of is something is backfeeding to the temp gauge from the block. It only happens when I hit the starter button. Any ideas? I do not have a ground strap from the motor to the frame. Could that be it? Everything worked before I took the motor out to be rebuilt. Thanks in advance.
OK, I added a ground strap from the starter to the frame. I ordered a new temp gauge and gas gauge. The gas gauge was working and everything seems to be fine. I fire up the motor and it fries the gas and temp gauge. I have now added a ground wire from the generator to the frame. Is there anything else it could be? I have a hot wire from the ignition switch to the "full" side of the gas gauge and the "empty" side goes to the sending unit. It worked fine before I started the motor. The temp gauge is just a mechanical gauge attached to the block. I'm going to order new gauges and I think I should be fine with the generator grounded. Any ideas? Thanks. I feel like a complete idiot about this.
Usually there is a gound running from the engine (block or head) to the body also. Seems like it might be overkill but I've always used one too.
You need grounds to/from battery/engine/frame/body. The first 3 should be battery cable or equivalent, 4th should be 10-12 gauge wire at minimum.
Thanks guys. I've got all the ground wires on so I'll install the new gauges when they come and see what happens.
A good ground from the battery to the frame, the frame to the motor, and DO NOT FORGET a good ground from the frame to the cab/firewall/dash
I agree with the others as far as grounds go..and their importance. I had a similar problem on an old car I had, turns out the mechanical temp sender cable/wire, was rubbing on a live wire, with the key in the on position. Might be worthwhile to get up under the dash, and check your routing of the sender cable/wire.
In 51 you should have a mechanical temperature gauge and a 6v fuel. Are you putting 12 volts to the fuel gauge? Also the fuel gauge insulator is marked sender and ignition, base your wiring off that.
I put a ground strap from battery to both the body/frame and the motor. Thats your $2 solution. (and clean + check all battery cable connections)
The only thing that would make the wires heat up like that is to try to draw heavy currents through them. You have something wired so that the starter is trying to draw current through those wires. When you try to start it again disconnect the gauges or you will be buying them by the case. Start it the first time with nothing but the starter circuit wired, the button, a hot wire to the coil you can get off quick, battery ground to the engine block and battery + to the big post on the solenoid. It should run. Somehow you are pulling starter current or at least solenoid current through your other circuits.
Battery - (or return if + grounded) should have it's cable going directly to the engine block. From the block install cables or straps to ground frame, firewall, hood (for radio interference). Depending on system voltage, cables <= 4 ga stranded for 12v, 2ga for 6v. This of course is for vehicles with battery adjacent to engine block. If battery mounted in trunk, then frame grounding will work, but be sure it is a full frame and not a unibody.
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