The wiring diagram shows what I think is a 2 prong flasher plugged into the fuse box. If GM had used a 3 prong flasher they could have had a less complicated turn signal switch (assuming I am right about how the switch supplies ground for the dash turn signal lamp) as well as using a standard one wire lamp socket for the dash turn indicator.
It almost sounds to me like your replacement turn signal switch does not do the job of the original switch. If that is the case and if a proper switch is not available there is a solution to this problem.
1. Cut the Dark Blue and Light Blue wires a couple of inches from the indicator lamp socket.
2. Add some wire to the Light Blue wire still attached to the socket. The other end of this wire needs to connect to ground.
3. Acquire two 1N4001 diodes. They are cheap. $5 for a package of 100 on Amazon. I probably have a few in the garage if you need them.
4. Twist the NON-stripe end of the two diodes together and also twist the Dark Blue wire from the lamp socket into this bundle. Apply solder.
5. Solder the loose end of the Dark Blue wire to the stripe end of one diode.
6. Solder the loose end of the Light Blue wire to the stripe end of the other diode.
Oooooooooooooooooooops! I forgot to tell you to put heat shrink tubing over all bare wires.
Last edited by Bill Hanlon; 08/02/2024 8:30 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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