70 Olds 442 Electrical Issue

[My442]

Here is a problem that has me scratching my head: I swapped out the engine harness and forward light harness from M&H Electric.
Good quality, and a basic R&R job.

Everything went well, except my oil pressure gauge (factory Rally Pac) now does not seem to have the same response when the engine is cold or hot. It seems that the gauge has a smaller response zone than before. The water temp gauge works fine.

Here is the troubleshooting that I have done so far:

1. Swapped out the sender with a new one - no change
2. Checked the sender ground - no change
3. Checked the crimp on the sender connector - no change
4. Split the harness from the bulkhead, and performed a continuity test - Test OK
5. Pulled the gauge and did a continuity test from the sender to the back of the gauge - Test OK

I am stumped, and will look to see if there is a grounding issue at the gauge.

Any ideas?

 

[StevieC]

Is the gauge of wire still the same size as it was before, that is going from the sender unit to the gauge? It could be that the wire is of a different size and it's causing a different resistance and leading to a false reading!

 

[My442]

The M&H folks claim the wire is the same size as the original.

It looks to be the same size and color.

 

[StevieC]

It could be not 100% copper and could contain some other metals causing resistance. Use an OHM meter and check the old wire and the new wire to see if they are different.

 

[eljefino]

Does the dash have any sort of voltage regulator for the instruments that may have been bypassed? How is the gas gauge?

 

[GMGuy]

If you suspect a ground issue, thats easy to check, get your jumper cables, clamp on to your under dash ground point and the other to the battery -ve and check guage response.
Have you got all your body grounds hooked up, specifically the engine compartment grounds? Block to firewall to get extremely specific.

 

[My442]

I will check the resistance....good idea.

 

[My442]

The body to engine grounds are clean and tight.

I am thinking of adding a ground wire to the gauge and retrying it.

 

[mechtech2]

Run an additional heavier wire and see if that clears it up. At least it will eliminate that factor [wire resistance too high].
You may also have a coincidence of a bad dash gauge.

 

[My442]

I checked the resistance of the original harness, and then did the same to the new harness. The readings were identical.

I pulled the gauge out of the dash, and found that the ground wire to the connector was not on properly. It worked its' way out of the connector.

So, a Radio Shack multi meter and some good old fashioned troubleshooting saved the day.

Lesson learned: Check the grounds and connections first!

 

[mechtech2]

442 - I could tell from your original post that you were a clear thinker around an automobile.
Nice work, Columbo!

 

[My442]

Originally Posted By: mechtech2
442 - I could tell from your original post that you were a clear thinker around an automobile.
Nice work, Columbo!


Thanks - hopefully, others will learn from my work.