I've been at this for years now *ug* Car gets mothballed as I don't want to tackle it. It's a 1999 M6 FRC C5 Corvette.

First I'm curious if there's a tool / multimeter adapter / probes that, can easily remove a fuse and check current draw from a circuit. I'm not blowing fuses, quite the opposite, I think a grounding issue so not getting enough current. I'd like to monitor current draw and see if I can find faulty ground / circuit that way (may just rig up a DMM and put a thermal fuse inline).

Background: my turn signals stopped working on front of the vehicle and IPC backlight flickered.

- I've gone through all under hood grounds, reworked, and tested them.

- Took apart headlamp & turn signal harnesses and found a dirty ground in turn signal to drive side connector. It's now clean.

- IPC fuse #19 on interior fuse block is good (I suspected issue there). All other fuses and relays seem fine both under hood and in passenger footwell. Open to suggestions / double checking them.

Made some progress. IPC doesn't flicker as MUCH now. However, speedometer doesn't work, and driver side daytime running light is dead (think is just bulb, will replace).

These problems are killing me. I REALLY don't want to dismantle the dash to check grounds behind it and or probe the VSS signal. Any tips are greatly appreciated.

 

Post number 15 in the thread below explains how to check current draw through fuses- without removing them from the panel:

https://www.corvetteforum.com/forums...t-charger.html

The turn signal issue may be related to the hazard switch contacts becoming corroded. First try turning the hazard lights off and on 20 times. If that brings back the turn signal lights, there are a number of ways to deal with the hazard switch including an LMC 5 bypass, drilling the switch and squirting cleaner/ lube into it*, replacing the switch and others.

Bad battery terminal contacts will cause the IC and interior lights to flicker or go off. Same with a bad battery. Battery terminal bolts should be at 11 foot pounds and clean. You should not be able to move the cable connection at the battery if tight. If you can, the battery bolt holes are shallow.

Report back.

* my solution for failing turn signals about 8 years ago- so far so good.

 

Just remove the suspect fuse and probe each terminal with your voltmeter set on the AMPS scale…most DVOM’s have a 10 amp fuse so if the current doesn’t exceed this you should be fine…or buy yourself an amp clamp and just place it around the suspect circuit wire.

 

Most amp clamp meters measure only AC current. You need a special and much more expensive clamp-on meter to measure DC current, they have to be calibrated and are not as accurate.And you have to chase down each wire to do this.
Easier to use the method in the video above posted by jim993 or place the VOM across the neg battery terminal and neg cable and measure the current draw after pulling each fuse one at a time out of the panel (PIA).

 

Todays AMP clamps measure BOTH…one on the left is $100.00 and accuracy of 1.5% and to “calibrate” all you do is push the blue button !!…on the right is $50.00 and measures both also..to calibrate push the button. The OP doesn’t have a parasitic draw and didn’t mention his battery going dead so pulling fuses will not help him and also pulling fuses is not the best way to do it…voltage drop is !!

 

Moved to C5 Tech.

 

I should have printed this and tried your suggestion. *personal gripe* part of my issue is it's VERY hard to get into the garage where my corvette is stored. My folks visit me for several months of the year and park in front of it... So I cannot get into there without playing musical cars

But you gave me some hope I've not driven the car for a couple years now aside from around the block because of this issue and would love to get it resolved.

 

Putting some notes here. I searched hazard switch problems... I've cleaned up all the engine bay grounds and splice packs. However, I couldn't find a decent diagram to show the rear splice packs, even after I bought the All Data DIY subscription.

This video shows another splice pack behind rear tail light
Pardon me, but what the HE double L was GM thinking using those dump splice packs on exterior of car. Previously I only saw them on interior.

Been searching and reading All Data DIY (sucks and is expensive don't buy it).

Check for corroded wires by PCM / under battery: I vaguely remember spilling something over the place years ago under the hood. Then I put something on it to soak it up... I don't think it was baking soda... but maybe it was... lastly flushing it off with a LOT of water. It was a huge mess. Maybe it was a leaky battery although I have AGM batteries. Long story short found a video to get at the PCM


Test Cruise Control: cruise control uses the VSS output of the PCM, not form the VSS sensor. If cruise works then the PCM is good. Otherwise, it's wire w/ VSS signal or PCM itself.

 

Notes: played with it a bit today.

Daytime Running Light Relays: when removed dash illumination stopped flickering. Must be issue in DRL circuit. No effect on VSS.

Gear Oil is Low: not sure if that effects VSS I need to top it off and see if that has any effect on my speedometer.

Speedometer Stepper Motor: is good, passes self check on startup.

 

Much closer.... Found a major issue and cleaned it up as best as possible.

First my question: VSS signal works now. Cluster passes stepper motor / self test. However, speedometer doesn't respond.

I need a way to diagnose the VSS signal to the cluster. I've done this on my truck. The PCM sends a 1hrz / 1mph square wave to the tachometer (5volts? or 12volts, I don't recall... I think was 5v). However, when I did that I had to tear apart the dash. I don't want to do that. Is there another way to check that signal? A connector somewhere? If nothing else, I'll splice into the harness for the PCM. I could also hook up a function generator and try to drive the cluster.

Second question: I found a electrical diagram with the VSS signal from the PCM to the IPC, Radio, Cruise Control, and BCM. It shows a splice S242 inside the vehicle. I'm assuming by the BCM? Anybody know where that splice is? Maybe it's loose?

Backstory:

I have virtually NO time to work on this car I get a few hours a month if that... Years ago I had a battery leak. I put baking soda on it... Then I ran water over the baking soda, but seems I didn't get it all off. I pulled the engine controller and it along with the frame and everything down there looked like it was raised from the titanic Thank god the harnesses work mostly clean. I spent several days detailing the frame. I had to soak it in distilled water, then use scuff pads to remove the baking soda residue. I got it all off, then resealed the frame with industrial / oil based paint. Lastly I had to take the blue and red connectors and soak them in vinegar and distilled water for a day or so. The baking soda came right off... I sprayed them w WD40 to remove water, let them set... Then used connector clearer solvent. Lastly I blew them dry as a bone with compressed air. Long story short, most of my electrical issues are gone now.

Dash lights don't flicker anymore. VSS signal works. I still do have a funky issue with driver side turn signal (bad bulb? unrelated? will figure it out). And the stupid speedometer isn't responding.

 

hi
my c6 2005 has got issues . speedo and digital not working and abs warning on ,its been packed in garage and was ok till i decided it was time to get out and give it a run ./has anyone any ides ? regards george

 

I don't have pinout for that... Possibly the serial data line? On mine there's two Vehicle Speed Signals. One is a 1hrz per 1mph pulse. The other is embedded in a serial data stream. I think it uses some hybrid approach to displaying speed... serial data and the pulses. In the least the cruise and BCM must use the serial data.

Long story short, it maybe the newer versions completely went to the serial data and what you're seeing is a complete loss of that data stream.

Do you have a scan tool? Can you pull the codes if any?

 

I continue to troubleshoot this bleeping issue. I have a larger thread on ls1Tech & Tahoe Yukon Forum. They sent me back here. It seems the grounds for my PCM are messed up. I thought I'd found all the grounding points and tested them. However, FSM has a G120 and S120 which I cannot find for the life of me. Anybody know where these are?

 

My 2001 FSM does not list a G120, but says S120 : Engine harness approximately 5.9" from the main harness in the branch leading to the powertrain control module connectors.

 

Thanks @jim993 really appreciate the help.

Yeah mine says that too. It's specific, yet I wonder, engine harness? Easier to trace the other way from the PCM out but they reference that branch. There's several branches....? I end up under the fuse panel and the coolant revivor which I've taken both of those apart before. Wish I had a picture or something more tangible to go on.

UPDATE I found S120 it was in the harness as FSB mentioned. Not sure what happened but my grounds are working for PCM now. However, speedometer still isn't working.