Tach backlight operational; now, instrumental lights aren’t

[Pearly72]

I’m stumped! Before I try to dissect it and mess things up more, I’m going to ask you guys - who have never led me astray before.

I hooked up a new Sunpro tach yesterday, which was given to me by the PO when I bought my truck. Red was jumped to an accessory fuse (a/c fuse: I don’t have a/c). Green, of course went to HEI, Black went to ground... and the WHITE (for tach backlight) was jumped to the Instrumental fuse at the top right corner (drawn on a generic photo attached).

After wiring it (first tach install I’ve done), all worked great. RPMs consistent and backlight worked. However, it was daytime and I didn’t check my instrumental lights. Drove it all day and all worked well... still does. However, when parking into the garage at dusk, I realized that my instrumental lights were not on!!! After adjusting the dimmer, still nothing.

White (tach light) wire install: stripped the wire about 3/8” and wedged it between the top of the fuse and the connector. The fuse did not look popped, but all I had was my phone flashlight. Should I have not hooked it up to the fuse this way and hooked it into the “feed” slot? I’m confused, because I figured the fuse would still have a complete circuit.

Has anyone experienced this? I knew I should’ve found some instructions! I will pull the fuse and make sure it didn’t blow when I have better light.

Before I screw things up even more, may I have some guidance? Thank you in advance!!

[dmjlambert]

The electricity flows from the headlight switch dimmer to the fuse clip you indicate with your big arrow, then through the fuse to the instrument cluster to light the 4 light bulbs in the instrument cluster. It also goes to the blade terminal right below the fuse. So the most correct place to get instrument light from is from that terminal below the fuse. Since you are getting power before it goes through the fuse, you are getting unfused power. I suggest test the fuse. You can't tell from looking if a fuse is good. Check for voltage with a test light or multimeter. I suggest get your voltage to send to the tach backlight from the terminal instead of from the input of the fuse. Some people have found so much rust on the fuse holders that electricity can't pass. If that's the case with yours, clean up the fuse holder clips and terminal, then re-insert the fuse.

[Pearly72]

Originally Posted by dmjlambert

The electricity flows from the headlight switch dimmer to the fuse clip you indicate with your big arrow, then through the fuse to the instrument cluster to light the 4 light bulbs in the instrument cluster. It also goes to the blade terminal right below the fuse. So the most correct place to get instrument light from is from that terminal below the fuse. Since you are getting power before it goes through the fuse, you are getting unfused power. I suggest test the fuse. You can't tell from looking if a fuse is good. Check for voltage with a test light or multimeter. I suggest get your voltage to send to the tach backlight from the terminal instead of from the input of the fuse. Some people have found so much rust on the fuse holders that electricity can't pass. If that's the case with yours, clean up the fuse holder clips and terminal, then re-insert the fuse.

Thank you for the advise! GM made it too easy for me and I still messed it up. I will do that, as recommended and I’ll update - just in case a rookie like me does this and needs some trouble shooting.

[Pearly72]

Originally Posted by Pearly72

Thank you for the advise! GM made it too easy for me and I still messed it up. I will do that, as recommended and I’ll update - just in case a rookie like me does this and needs some trouble shooting.

Ok! All is functioning as intended. DMJLAMBERT, thank you for taking the few minutes to explain, I really appreciate it. I learned the lesson not to wing it and hack things, opposed to do it right. In this case, it would’ve taken the same time.

I must’ve blown the fuse to the instrumentals. Replaced it and hooked the white wire to the spare location, as I did the red wire to the “key on” spare slot. All functions well. Thank you for your guidance... and thanks GM engineers of the early years.

[dmjlambert]

Good deal. Notice how the accessory you have plugged into the CIG terminal has a piggyback connector. That is in case you want to plug in yet another accessory that is powered all the time. An example of typical use on these trucks is the cigar lighter will be plugged in there, and the air conditioner blower motor high speed power to the blower relay will be piggybacked onto it. You could do the same thing if you find in the future you have need for more instruments to provide dimmer light power to, such as some sort of heater or A/C control lighting or some other gizmo. GM original style connectors like the one plugged into the CIG outlet, and its piggyback, are called Packard 56 connectors and are available online, such as on eBay.

[Pearly72]

Originally Posted by dmjlambert

Good deal. Notice how the accessory you have plugged into the CIG terminal has a piggyback connector. That is in case you want to plug in yet another accessory that is powered all the time. An example of typical use on these trucks is the cigar lighter will be plugged in there, and the air conditioner blower motor high speed power to the blower relay will be piggybacked onto it. You could do the same thing if you find in the future you have need for more instruments to provide dimmer light power to, such as some sort of heater or A/C control lighting or some other gizmo. GM original style connectors like the one plugged into the CIG outlet, and its piggyback, are called Packard 56 connectors and are available online, such as on eBay.

Good to know this, thank you for the insight!