'70 horn relay / ammeter

[Donn M.]

Replaced dichromate cap horn relay w/Delco silver cap. Took pics. and drew diagram first as electrical is one of my weaknesses. Started car and horn, key buzzer and all gauges worked except ammeter shows 40 minus. Rechecked wire hookup and found a red wire that I did not get back on. This car has 3 red wires at relay. Still no voltage at gauge. Put old relay back on with same result.
Battery shows 12.7 and 14.5 when running. Test light comes on at all wires at horn relay and on both sides of fuse links. Only oddity to me is horn honks when I probe black wire plugged in next to green horn wire under relay.
Checked fuses. All fuses show positive on both sides except small bottom 5 amp which shows nothing on any of the 4 metal clips that hold the fuse. Replaced fuse anyway. Does a wire from the relay have anything to do with the voltage gauge ?
I have trouble reading a wiring diagram, but I think it shows both ammeter gauge wires go to the fuse box, right ?
Have read all past archives on this subject, studied AM and wiring diagram and am lost.
Any help/direction will be appreciated. Donn

[Mark E.]

Re: '70 horn relay / ammeter

The Battery gauge shows the voltage differential between the starter solenoid and the buss on the horn relay. A negative reading on the gauge can be caused by a bad connection of the 20 gauge orange lead (orange for 1973; probably the same for '70) to the horn relay buss. So double check that all buss and wire terminals are clean and tight.

Also disconnect the battery for a few seconds to discharge any residual voltage in the gauge windings.

[Donn M.]

Re: '70 horn relay / ammeter

Mark, Thanks for the reply. The only orange wire @ my horn relay is a fuse link, approx. # 12 -14. It reduces to about a # 16 black w/white stripe that goes into a harness I trace to the fuse block plug. The battery has been disconnected several times when I have replaced the relays and when not working on the car. I noticed a black fuse link going to a red wire at the starter solenoid that looks suspicious. I'll take apart later and see what I can find. I've been searching for fuse links with no success. Any suggestions?
Thanks again for your help, Donn

[Mark E.]

Re: '70 horn relay / ammeter

There's a 20 org and 16 black using the same terminal connected to the horn relay buss. Within a few inches, the 20 org goes to a fusible link, then becomes a 16 b/w wire. This wire goes to the bulkhead then to the Battery gauge. Check continuity of this wire from the buss to the bulkhead connector.

The 16 black also goes to a fusible link within a few inches, then becomes a 12R wire. This goes to the headlamp switch via the bulkhead connector. This lead probably isn't your issue.

Also on the horn relay buss should be:

- 10R that goes to the starter solenoid. It has a fusible link near the solenoid. Connected to it near here is another fusible link that goes into a 14 Black wire. This lead goes to the other side of the Battery gauge via the bulkhead connector. Given your issue, check this for continuity between the solenoid and bulkhead connector.

- 10R that goes to the alternator

- 10R with an inline fuse for AC (if you have this)

- 10R for PW (if you have this)

Hope this helps.

[Donn M.]

Re: '70 horn relay / ammeter

Mark, Thank you so much for the help. Very clear information that I needed. Had checked the fusible link at the solenoid and it appears the problem. Found a new GM replacement and have on order. Have PW and had suspected that might be the 3rd Red.
Mark, you have been extremely helpful.
Thanks again, Donn

[Donn M.]

Re: '70 horn relay / ammeter

Responding to a past thread. After a couple of PMs with Mark and having replaced a couple fuse links, I removed the right-side dash and was able to disconnect and pull out the battery gauge connector. Both wires gave a 12+ reading so ordered a new gauge that I was able to hook up and got positive readings. So problem was found, but now the much dreaded console, radio, cluster gauge removal. I've done this before a couple of times for other reasons and always say I will never do it again.
Delays of a bout with RSV (you don't want that virus), back spasms and some other lame excuses I finished the project, everything works and I can say, I never do that again.
Mark, thanks for your guidance in finding the problem. Your PMs were very helpful.

[Mark E.]

Re: '70 horn relay / ammeter

Responding to a past thread. After a couple of PMs with Mark and having replaced a couple fuse links, I removed the right-side dash and was able to disconnect and pull out the battery gauge connector. Both wires gave a 12+ reading so ordered a new gauge that I was able to hook up and got positive readings. So problem was found, but now the much dreaded console, radio, cluster gauge removal. I've done this before a couple of times for other reasons and always say I will never do it again.
Delays of a bout with RSV (you don't want that virus), back spasms and some other lame excuses I finished the project, everything works and I can say, I never do that again.
Mark, thanks for your guidance in finding the problem. Your PMs were very helpful.

You're welcome. I feel your pain regarding tearing into C3 dashes. I'm afraid my back is facing replacing a distributor on a C4 LT1. I hope it holds up (my back, that is).